Blade assembly with selective flow blocking arrangement for wind assisted ship propulsion and ship having such blade assembly

Abstract

Herein is disclosed a blade assembly (1) for providing wind propulsion for a ship (2), as well as such ship (2) having one or more blade assemblies (2), the blade assembly (1) comprising a top end part and a lower end part for being coupled to a part of the ship (2), and a first and a second aerofoil assembly (3, 4), each of the and the second aerofoil assembly (3, 4) comprising at least two aerofoils (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c'), wherein the first aerofoil assembly (3) is arranged at one side of a central plane (CP) of the blade assembly (1) and the second aerofoil assembly (4) is arranged at the opposite side of the central plane (CP) than the first aerofoil assembly (3), wherein the at least two aerofoils (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c') of each of the first and the second aerofoil assembly (3, 4) are oriented with a leading edge (LE) of the aerofoil (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c') towards an inlet gap (IG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4), wherein the at least two aerofoils (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c') of each of the first and the second aerofoil assembly (3, 4) are arranged in an overlapping sequence so that one or more flow channels (FC) are formed between neighbouring aerofoils (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c'), and wherein for each of the first and the second aerofoil assembly (3, 4) an assembly camber line (ACAL) connecting the leading edge (LE) of the front aerofoil (5a, 5a', 105a, 105a') nearest the inlet gap (IG) with the trailing edges (TE) of each of the aerofoils (5a, 5a', 5b, 5b', 5c, 5c', 105a, 105a', 105b, 105b', 105c, 105c') in the aerofoil assembly (3, 4) from the front aerofoil (5a, 5a', 105a, 105a') towards the back aerofoil (5b, 5b', 105b, 105b') nearest an outlet gap (OG) of the blade assembly (1) deviates from an assembly chord line (ACHL) connecting the leading edge (LE) of the front aerofoil (5a, 5a', 105a, 105a') with the trailing edge (TE) of the back aerofoil (5b, 5b', 105b, 105b') in a direction with a component away from the central plane (CP), the blade assembly (1) further comprising a flow blocking arrangement (10, 11, 13, 14) which can be selectively shifted between a first position, where flow of air from the inlet gap (IG) and out through the flow channel(s) (FC) of the first aerofoil assembly (3) is limited, and a second position, where flow of air from the inlet gap (IG) and out through the flow channel(s) (FC) of the second aerofoil assembly (4) is limited.

Description

[0001] BLADE ASSEMBLY WITH SELECTIVE FLOW BLOCKING ARRANGEMENT

[0002] FOR WIND ASSISTED SHIP PROPULSION AND SHIP HAVING SUCH BLADE

[0003] ASSEMBLY

[0004] A blade assembly is disclosed for wind assisted ship propulsion as well as a ship comprising such blade assembly, where the blade assembly is provided with a flow blocking arrangement that can be selectively shifted for use for incoming wind from starboard as well as port side of the ship.

[0005] Background

[0006] Use of sails for propulsion of marine vessels by means of wind has been known since antiquity, and a combination of sails and motor propulsion is well known. Modem wind assisted ship propulsion (WASP) of larger marine vehicles equipped with motor driven propulsion means for reducing the consumption of fuel include the Flettner rotor utilizing the Magnus effect and other rigid structures like two or three consecutive symmetrical aerofoils as shown in US patent applications US 2019 256182 and US 2023 002023, where the individual aerofoils can be turned about vertical axes to adapt the structure for incoming wind from the starboard as well as from the port side of the ship, and wherein the whole structure can be turned about a vertical axis to adjust for the angle of the wind with respect to the direction of movement of the ship hull.

[0007] A different solution is presented in Japanese patent application JP 2019 108046, where each structure for wind propulsion of the marine vehicle comprises two sets of blades, where each set of blades is designed for incoming wind from starboard and port side, respectively, and wherein each set of blades are arranged rotatably about a horizontal axis so that only the set of blades in use is vertical while the other set of blades is lowered to a more horizontal position. Each structure can furthermore be turned about a vertical axis for adapting to the direction of wind with respect to the direction of the ship hull.

[0008] US patent US 4,848,258 discloses a sail comprised by a plurality of aerofoils in a row, where the individual aerofoils are asymmetrical, but the sail is overall symmetrical from front to back and is rotatable about a vertical mast to allow adjustment to the direction of the wind and to shift between incoming wind from starboard and port side by rotating the sail and shifting the position of the front end and the back end of the sail. It is a general requirement for wind assisted ship propulsion arrangements that it can be used for a range of directions of the incoming wind, including starboard as well as port side wind.

[0009] Brief description of the invention

[0010] The present invention provides according to a first aspect a blade assembly having a first aerofoil assembly and a second aerofoil assembly arranged on each side of a central plane and both aerofoil assemblies curving away from the central plane, so that the aerofoil assemblies are arranged for starboard and port side wind, respectively. Each aerofoil assembly comprises at least two overlapping aerofoils forming a flow channel for directing air coming in through the inlet gap between the aerofoil assemblies out into the boundary layer of the aerofoil assembly in action, i.e. having a suction side and thereby reducing the risk of separation of the boundary layer of the suction side. A flow blocking arrangement is provided which can be shifted between allowing a flow of air from the inlet gap and out through the flow channel(s) of the first aerofoil assembly while limiting the flow of air out through the flow channel(s) of the second aerofoil assembly, to allowing a flow of air out through the flow channel(s) of the second aerofoil assembly while limiting the flow of air out through the flow channel(s) of the first aerofoil assembly. This flow blocking arrangement provides for a better reduction of the risk of separation of the boundary layer of the suction side and a more stable flow of air through the blade assembly, thus reducing or avoiding losses due to unstable flow patterns and generation of vibration or resonance in the blade assembly. Furthermore, the flow blocking arrangement may allow for a more optimal adjustment of the blade assembly with respect to the apparent incoming direction of the wind so as to achieve an improved propulsion of the ship.

[0011] Thus, the present invention according to the first aspect relates to a blade assembly for providing wind propulsion for a ship, the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship, and a first aerofoil assembly and a second aerofoil assembly, each of the first aerofoil assembly and the second aerofoil assembly comprising at least two aerofoils, wherein the first aerofoil assembly is arranged at one side of a central plane of the blade assembly, the central plane extending between the top end part and the lower end part and encompassing a central longitudinal axis of the blade assembly, and the second aerofoil assembly is arranged at the opposite side of the central plane than the first aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are oriented with a leading edge of the aerofoil towards an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils, and wherein for each of the first aerofoil assembly and the second aerofoil assembly an assembly camber line connecting the leading edge of the front aerofoil nearest the inlet gap with the trailing edges of each of the aerofoils in the aerofoil assembly from the front aerofoil towards the back aerofoil nearest an outlet gap of the blade assembly deviates from an assembly chord line connecting the leading edge of the front aerofoil with the trailing edge of the back aerofoil in a direction with a component away from the central plane, the blade assembly further comprising a flow blocking arrangement which can be selectively shifted between a first position, where flow of air from the inlet gap and out through the flow channel(s) of the first aerofoil assembly is limited, and a second position, where flow of air from the inlet gap and out through the flow channel(s) of the second aerofoil assembly is limited.

[0012] Each of the first aerofoil assembly and the second aerofoil assembly may comprise one or more intermediate aerofoil between the front aerofoil and the back aerofoil, wherein all the aerofoils of an aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils. The aerofoil assemblies comprises preferably 2 to 5 intermediate aerofoils, such as 3 or 4.

[0013] The central plane of the blade assembly preferably extends as a straight plane from the lower end part to the top end part of the blade assembly, and the first and second aerofoil assemblies extend parallel to the central plane of the blade assembly. The flow channels are formed between neighbouring aerofoils so that the aerofoil closest to the inlet gap of the blade assembly overlaps the other aerofoil, so that the overlapping part has a larger distance to the central plane than the overlapped part of the other aerofoil.

[0014] The assembly camber line defines an overall camber line for each of the aerofoil assemblies and specifies that each aerofoil assembly has an overall asymmetry with an assembly camber line deviating from the assembly chord line in a direction away from the central plane.

[0015] In a preferred embodiment, the camber line of each of the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly deviates from the chord line of the aerofoil with a component in a direction away from the central plane.

[0016] In a preferred embodiment, the flow blocking arrangement comprises a movable wing element extending in the longitudinal direction of the blade assembly, i.e. in a direction parallel to the central longitudinal axis. The wing element is preferably arranged to pivot around a pivot axis extending in the longitudinal direction of the blade assembly.

[0017] The pivot axis extends in one preferred embodiment along the central plane of the blade assembly between the central longitudinal axis of the blade assembly and an outlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly.

[0018] The pivot axis extends in a second preferred embodiment along the central plane of the blade assembly between the central longitudinal axis of the blade assembly and an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly.

[0019] The flow blocking arrangement may further comprise a stationary barrier extending between the movable wing element and an outlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly. The stationary barrier extends in the longitudinal direction of the blade assembly parallel to the first and the second aerofoil assembly as well as to the movable wing element.

[0020] It is advantageous that the flow blocking arrangement further comprises guide vanes near the leading edge of the movable wing element, the guide vanes being movable together with the movable wing element, the guide vanes being provided to decrease the separation of flow near the leading edge of the movable wing element, when the flow comes from the inlet gap of the blade assembly.

[0021] The present invention provides according to a second aspect a blade assembly having a first aerofoil assembly and a second aerofoil assembly arranged on each side of a central plane and both aerofoil assemblies curving away from the central plane, so that the aerofoil assemblies are arranged for starboard and port side wind, respectively. Each aerofoil assembly comprises at least two overlapping aerofoils forming a flow channel for directing air coming in through the inlet gap between the aerofoil assemblies out into the boundary layer of the aerofoil assembly in action, i.e. having a suction side and thereby reducing the risk of separation of the boundary layer of the suction side. A stationary barrier is provided between the first aerofoil assembly and the second aerofoil assembly and forming barrier flow channels between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly, respectively.

[0022] The stationary barrier provides for a better reduction of the risk of separation of the boundary layer at the rear part of the suction side of the aerofoil assembly in action, i.e. around the back aerofoil thereof due to the injection of air with a higher kinetic energy into the boundary layer near the rear part of the suction side through the barrier flow channel formed between the stationary barrier and the back aerofoil of the aerofoil assembly in action. Hereby, the stall angle of the aerofoil assembly may be increased and the aerofoil assembly may contribute to the propulsion of the ship on which it is installed at a wider range of angles of the incoming wind. Furthermore, a more stable flow of air through the blade assembly may be achieved, thus reducing or avoiding losses due to unstable flow patterns and generation of vibration or resonance in the blade assembly.

[0023] Thus, the present invention according to the second aspect provides a blade assembly for providing wind propulsion for a ship, the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship, and a first aerofoil assembly and a second aerofoil assembly, each of the first aerofoil assembly and the second aerofoil assembly comprising at least two aerofoils, wherein the first aerofoil assembly is arranged at one side of a central plane of the blade assembly, the central plane extending between the top end part and the lower end part of the blade assembly and encompassing a central longitudinal axis of the blade assembly, and the second aerofoil assembly is arranged at the opposite side of the central plane than the first aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are oriented with a leading edge of the aerofoil towards an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils, and wherein for each of the first aerofoil assembly and the second aerofoil assembly an assembly camber line connecting the leading edge of the front aerofoil nearest the inlet gap with the trailing edges of each of the aerofoils in the aerofoil assembly from the front aerofoil towards the back aerofoil nearest an outlet gap of the blade assembly deviates from an assembly chord line connecting the leading edge of the front aerofoil with the trailing edge of the back aerofoil in a direction with a component away from the central plane, the blade assembly further comprising a stationary barrier extending between the first aerofoil assembly and the second aerofoil assembly and forming barrier flow channels between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly, respectively.

[0024] Each of first aerofoil assembly and the second aerofoil assembly may comprise one or more intermediate aerofoil between the front aerofoil and the back aerofoil, wherein all the the aerofoils of an aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils. The aerofoil assemblies comprises preferably 2 to 5 intermediate aerofoils, such as 3 or 4.

[0025] In a preferred embodiment, the camber line of each of the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly deviates from the chord line of the aerofoil with a component in a direction away from the central plane. The below optional features are applicable to aerofoil assemblies of the first aspect of the present disclosure as well as to the second aspect of the present disclosure.

[0026] The stationary barrier is preferably arranged symmetrically around and extending along the central plane of the blade assembly.

[0027] In some embodiments, the central longitudinal axis extends within the stationary barrier, whereas the central longitudinal axis in other embodiments extends externally to the stationary barrier, preferably so that the stationary barrier extends between the central longitudinal axis and the outlet gap.

[0028] The barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are preferably of a width of at least 0.01 times of the chord length of the respective back aerofoil, the extent being measured in the direction perpendicular to the chord line of the respective back aerofoil, such as in the range of 0.01 to 0.4 time the chord length, preferably within 0.05 to 0.4 times the chord length.

[0029] The barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are preferably of an extent of at least 0.02 times of the chord length of the respective back aerofoil, the extent being measured in the direction of the chord line of the respective back aerofoil, such as in the range of 0.02 to 0.8 time the chord length, preferably within 0.1 to 0.5 times the chord length.

[0030] The barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are preferably converging towards the trailing edge of the back aerofoils, such as by at least 0.1 times the width of the flow channel from an inlet of the flow channel to an outlet of the flow channel, such as in the range of 0.1 to 0.9 times the width, preferably within the range of 0.2 to 0.5 times the width.

[0031] Furthermore, it is preferred that the blade assembly includes at least one support structure connecting each of the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly at a position between the top end part and the lower end part of the blade assembly and the support structure is also connected to the optional stationary barrier of the blade assembly, at a position between the top end part and the lower end part of the blade assembly.

[0032] The support structure or structures are provided to enhance the mechanical stability of the blade assembly by rigidly connecting each of the aerofoils of the two aerofoil assemblies at one or more positions along the length of the blade assembly, and also rigidly connect to the stationary barrier, if it is provided in the blade assembly. Preferably, at least one of such support structures is positioned at least 1 / 3 of the full longitudinal extent for the blade assembly from the lower end part of the blade assembly, such as at least 2 / 3 of the full longitudinal extent. The support structure may be placed at the top end part of the blade assembly.

[0033] The support structure or structures may be applied to manufacture or construct the blade assembly in a modular form, such as by 2 to 5 modules in the longitudinal direction of the blade assembly, where the modules can be separated from each other and e.g. a movable wing element may be present in each of the modules of the blade assembly.

[0034] The blade assembly when mounted on a ship takes up a certain amount of space of the ship’s deck and since the blade assembly will be rotated around its vertical yaw axis, i.e. the central longitudinal axis, the space occupied by the blade assembly is substantially circular in the horizontal plane. This space should be used as efficiently as possible to obtain wind propulsion for the ship, which may be achieved by a blade assembly that is of a substantial width as compared to the length of the blade assembly, provided that the boundary layer will remain attached to the aerofoil assembly on the suction side, which is controlled e.g. by the design of the flow channels between the aerofoils.

[0035] It is preferred that the maximal width of the blade assembly perpendicularly to the central plane constitutes at least 0.4 times the lateral length of the blade assembly, such as at least 0.6 times the lateral length of the blade assembly, preferably in the range of 0.8 to 1.2 times the lateral length of the blade assembly, the lateral length of the blade assembly being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, and the maximal width of the blade assembly is the largest distance perpendicularly to the central plane between outer surfaces of the first aerofoil assembly and the second aerofoil assembly.

[0036] Alternatively or additionally, the smallest distance from the central longitudinal axis to the outer surface of any of the at least two aerofoils of the first aerofoil assembly and the at least two aerofoils of the second aerofoil assembly is preferably at least 40% of the largest distance from the central longitudinal axis to the outer surface of any of the at least two aerofoils of the first aerofoil assembly and the at least two aerofoils of the second aerofoil assembly, preferably at least 60% of the largest distance, and more preferred at least 80% of the largest distance.

[0037] The central longitudinal axis is the vertical yaw axis around which the blade assembly is intended to be rotated for adjusting the angle of the blade assembly with respect to a longitudinal axis of the ship.

[0038] The flow channels between any two neighbouring aerofoils of the first aerofoil assembly and of the second aerofoil assembly is preferably of an extent of at least 0.02 times of the chord length of that of the two aerofoils closest to the inlet gap of the blade assembly, the extent being measured in the direction of the chord length of that aerofoil, such as in the range of 0.02 to 0.8 time the chord length, preferably within 0.1 to 0.5 times the chord length.

[0039] The flow channels between any two neighbouring aerofoils of the first aerofoil assembly and of the second aerofoil assembly are of a width of at least 0.01 times of the chord length of that of the two aerofoils closest to the inlet gap of the blade assembly, the extent being measured in the direction perpendicular to the chord length of that aerofoil, such as in the range of 0.01 to 0.4 time the chord length, preferably within 0.05 to 0.4 times the chord length.

[0040] It is preferred that least one of the flow channels between neighbouring aerofoils each of the first aerofoil assembly and the second aerofoil assembly, and preferably all of the flow channels between neighbouring aerofoils of the first aerofoil assembly and the second aerofoil assembly, converges towards the trailing edge of the neighbouring aerofoils, such as by at least 0. 1 times the width of the flow channel, from an inlet of the flow channel to an outlet of the flow channel, such as in the range of 0.1 to 0.9 times the width, preferably within the range of 0.2 to 0.5 times the width.

[0041] The first aerofoil assembly of the blade assembly is preferably symmetrical with the second aerofoil assembly about the central plane extending between the top end part and the lower end part and encompassing a central longitudinal axis of the blade assembly. However, asymmetrical design of the first aerofoil assembly and the second aerofoil assembly is possible within the scope of the present invention.

[0042] The width of the inlet gap being the smallest distance between the first aerofoil assembly and the second aerofoil assembly near the inlet gap is preferably at least 0.1 times the lateral length of the blade assembly, the lateral length being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, such as within the range of 0. 1 to 0.8 times the lateral length of the blade assembly, preferably within the range of 0.3 to 0.6 times the lateral length of the blade assembly.

[0043] The outlet gap may in principle be of zero width, the width of the outlet gap being the smallest distance between the first aerofoil assembly and the second aerofoil assembly, provided that the flow channels are sufficiently wide to allow air to escape the space between the first aerofoil assembly and the second aerofoil assembly without causing an excessive pressure build-up in that space.

[0044] However, it is preferred that the outlet gap is at least 0.01 times the lateral length of the blade assembly, the lateral length being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, such as within the range of 0.01 to 0.2 times the lateral length of the blade assembly, preferably within the range of 0.05 to 0.15 times the lateral length of the blade assembly.

[0045] The blade assembly is preferably of a longitudinal extent of more than 20 meter, such as more than 30 meter, in particular in the range of 20 to 80 meter, such as in the range of 30 to 60 meter or in the range of 20 to 30 meter.

[0046] These are preferred longitudinal extents of the blade assembly. Longer blade assemblies, such as above 100 meters, such as in the range of 100 to 150 meters are not unreasonable or unrealistic, but puts higher demands on the safety systems allowing the blade assembly to reduce the aerodynamical load on the blade assembly, such as to yaw out of the wind and obtain a state where the incoming wind will not generate a lift force on first aerofoil assembly and the second aerofoil assembly combined.

[0047] In a preferred embodiment, a flow limiting structure is provided at the top end part of the blade assembly for reducing the unwanted and efficiency-reducing tip effect of the blade assembly, where air will flow in the longitudinal direction of the blade assembly from the pressure side of the blade assembly to the suction side of the blade assembly. The flow limiting structure extends preferably at least 0.1 time the lateral length of the blade assembly beyond the first aerofoil assembly and the second aerofoil assembly in a direction away from the central plane of the blade assembly at the position of the maximal width of the blade assembly, the lateral length of the blade assembly being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, and the maximal width of the blade assembly is the largest distance perpendicularly to the central plane between outer surfaces of the first aerofoil assembly and the second aerofoil assembly, such as in the range of 0. 1 to 0.75 times the lateral length of the blade assembly, preferably in the range of 0.2 to 0.5 times the lateral length of the blade assembly.

[0048] The flow limiting structure may constitute at least one of the support structures of the blade assembly.

[0049] At least one of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly may further comprise one or more vortex generators on the outer surface of the aerofoils and / or on the flow blocking arrangements. The use of vortex generators could reduce the risk of flow separation by generating a vortex, which delays local flow separation and aerodynamic stalling by removing some part of the slow-moving boundary layer that is in contact with the surface of the aerofoil. The one or more vortex generators may be placed on the outer surface of the front aerofoil of each of the first aerofoil assembly and the second aerofoil assembly. The one or more vortex generators may be placed close to the front side of the movable wing element of the flow blocking arrangement. The risk of flow separation may be increased close to the leading edge of the front aerofoils or close to the front side of the movable wing element, due to the larger angles of attack. The one or more vortex generators may extend over a length of preferably up to 0. 1 times of the longest chord length of any of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly. The one or more vortex generators may extend over a height from the outer surface of the aerofoils or from the flow blocking arrangement preferably by up to 0.05 times of the longest chord length of any of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly.

[0050] The present invention further relates to a ship comprising at least one blade assembly as disclosed herein, wherein each blade assembly is coupled to a yaw drive for adjusting the angle of the blade assembly with respect to a longitudinal axis of the ship.

[0051] The yaw drive is preferably arranged to rotate the blade assembly around the central longitudinal axis of the blade assembly.

[0052] The ship may further comprise a controller for controlling the yaw drive(s) of the ship, the controller being arranged to receive data indicative of wind direction or wind velocity, i.e. speed and direction of the wind accordingly by operating the yaw drive(s) in response to received data on wind direction or velocity. The wind direction and speed is, in case it is measured with an anemometer or other instrument on board the ship, the apparent wind speed and direction.

[0053] The controller furthermore is arranged to control the shifting of the flow blocking arrangement between the first position and the second position of the flow blocking arrangement in response to received data on wind direction and possible of the wind speed.

[0054] Brief description of figures

[0055] Fig. 1 shows a cross-section of a first embodiment of a blade assembly according to the present disclosure,

[0056] Figs. 2a-2b show a cross-section of a first embodiment of a blade assembly according to the present disclosure with the flow blocking arrangement in a first and second position,

[0057] Figs. 3-7 show a cross-section of other embodiments of a blade assembly according to the present disclosure,

[0058] Fig. 8 shows an example of streamlines from an airflow simulation through a cross section of the first embodiment of the blade assembly, Figs. 9-10 show the placement of an embodiment of the blade assembly on a ship,

[0059] Fig. 11 shows a cross-section of a first embodiment of a blade assembly according to the present disclosure, where the camber line and chord line of the first and second aerofoil assembly are defined,

[0060] Fig. 12 shows a cross-section of a first embodiment of a blade assembly according to the present disclosure, with a zoomed in area where the flow channel length and width are defined,

[0061] Figs. 13-14 show a cross-section of a first embodiment of a blade assembly according to the present disclosure, where the geometry of the blade assembly is defined in terms of the distances from the central longitudinal axis and length and maximal width in the lateral plane,

[0062] Fig. 15 shows a cross-section of an embodiment of a blade assembly according to the present disclosure, where vortex generators are placed on all aerofoils and the flow blocking arrangement of the blade assembly,

[0063] Fig. 16 shows a cross-section of an embodiment of a blade assembly according to the present disclosure, where vortex generators are placed on the front aerofoils and the front of the movable wing element of the blade assembly, with a zoomed in area showing a single vortex generator on the aerofoil,

[0064] Figs. 17-20 show various embodiments of blade assemblies comprising a stationary barrier, and

[0065] Fig. 21 shows a ship equipped with a blade assembly, a yaw drive, a wing drive and a controller for rotating of the blade assembly and the wing element.

[0066] Detailed description of embodiments

[0067] A cross-section of a first embodiment of a blade assembly 1 is shown in Fig. 1, comprising a first aerofoil assembly 3 and a second aerofoil assembly 4, which are mutually symmetrical around the central plane CP of the blade assembly, in which the lateral length LI of the blade assembly 1 extends. Each of the first aerofoil assembly 3 and the second aerofoil assembly 4 comprising at least two aerofoils, where the front aerofoil 5a, 5a’ and the back aerofoil 5b, 5b’ and the potentially intermediate aerofoils 5c, 5c’ are oriented with a leading edge LE of the aerofoil towards an inlet gap IG of the blade assembly between the first aerofoil assembly 3 and the second aerofoil assembly 4 and arranged in an overlapping sequence so that flow channels FC are formed between neighbouring aerofoils. Each of the front aerofoils 5a, 5a’, back aerofoils 5b, 5b’ and intermediate aerofoils 5c, 5c’ are non-symmetric aerofoils, with the camber line CAL deviating from the chord line CHL in the direction away from the central plane CP. The chord length CL from the leading edge LE to the trailing edge TE is indicated on Fig. 1 for one aerofoil 5a’.

[0068] The blade assembly 1 in Fig. 1 is provided with a flow blocking arrangement 10 between the first aerofoil assembly 3 and the second aerofoil assembly 4. The flow blocking arrangement 10 comprises a movable wing element 11 extending from a pivot axis 12 extending along the central plane CP and forwards towards the inlet gap IG of the blade assembly 1. In this embodiment of the invention, the pivot axis extends between the central longitudinal axis 7 and the inlet gap IG. The front part of the movable wing element 11 is provided with guide vanes 14 on each side of the leading edge of the movable wing element 11 to prevent separation of the flow around the front part of the movable wing element 11 when the movable wing element 11 is in its first position or its second position as shown in Figs. 2a and 2b and the blade assembly 1 is in operation for providing propulsion to a ship 2. The flow blocking arrangement 10 comprises furthermore a stationary barrier 13 extending from the pivot axis 12 towards the outlet gap OG of the blade assembly 1, the stationary barrier 13 being arranged symmetrically around and extending along the central plane CP of the blade assembly 1.

[0069] The blade assembly 1 in Fig. 1 is provided with a stationary barrier 13 extending from the pivot axis 12 towards the outlet gap OG of the blade assembly 1, the stationary barrier 13 being arranged symmetrically around and extending along the central plane CP of the blade assembly 1. Barrier flow channels FCB are formed between the sides of the stationary barrier 13 and the back aerofoils 5b, 5b’ having generally the same characteristics as the flow channels FC formed between neighbouring aerofoils.

[0070] The position of the movable wing element 11 in Fig. 1 is a neutral position, where the movable wing element 11 extends along the central plane CP of the blade assembly 1. When the blade assembly is in operation for providing propulsion of a ship, the movable wing element 11 is rotated to either a first position as shown in Fig. 2a, where the movable wing element 11 is turned towards the first aerofoil assembly 3 to limit the flow of air coming from the inlet gap IG and out through the flow channels FC of the first aerofoil assembly 3 while allowing the flow of air to pass the flow channels FC of the second aerofoil assembly 4. The movable wing element 11 is rotated to the first position of Fig. 2a when the apparent wind has an incoming direction from starboard of the ship 2, i.e. from the right hand side of the ship 2 when facing the front of the ship 2. With the apparent wind direction being from the port side of the ship 2, the movable wing element 11 is rotated to the second position shown in Fig. 2b, where the movable wing element 11 is turned towards the second aerofoil assembly 4 to limit the flow of air coming from the inlet gap IG and out through the flow channels FC of the second aerofoil assembly 4 while allowing the flow of air to pass the flow channels FC of the first aerofoil assembly 3.

[0071] The function of the flow blocking arrangement 10 in the embodiment shown in Figs. 1, 2a and 2b is furthermore to allow for a more smooth and stable flow of air through the blade assembly 1, providing for a reduction of losses due to unstable flow as well as reduction of possible vibrations caused by unstable flow pattern and generated vortices.

[0072] A cross-section of other embodiments of a blade assembly 1 are shown in Figs. 3-7, each comprising a first aerofoil assembly 3 and a second aerofoil assembly 4. Each of the blade assemblies 1 comprises first and second aerofoil assemblies 3, 4 similar to the ones of the first embodiment shown in Figs. 1, 2a and 2v but with different flow blocking arrangements 10. The embodiment of Fig. 3 is similar to the first embodiment of Fig. 1, except that this one is not provided with guide vanes 14. The embodiment of Fig. 4 comprises a movable wing element 11 with a pivot axis 12 positioned close to the outlet gap OG of the blade assembly 1 between the central longitudinal axis 7 and the outlet gap OG and this embodiment is not provided with a stationary barrier 13. The embodiment shown in Fig. 5 comprises a stationary barrier 13 of a substantially circular cross-section and a movable wing element 11 with a pivot axis position between the central longitudinal axis 7 and the outlet gap OG. The embodiment of Fig. 6 comprises a stationary barrier 13 in the shape of a platelike element extending in the lateral direction of the blade assembly 1 and a movable wing element 11 with a pivot axes 7 between the inlet gap IG and the central longitudinal axis 7. The embodiment shown in Fig. 7 comprises a stationary barrier 13 in the shape of a bulky, symmetrical element extending in the lateral direction of the blade assembly 1 and a movable wing element 11 with a pivot axes 7 between the inlet gap IG and the central longitudinal axis 7.

[0073] The aerofoils of the first and the second aerofoil assemblies 3, 4 can be of various types as the thin aerofoils shown in the first embodiment, where some of the thin aerofoils also comprise a cylindrical element CE, such as a tube, attached at the leading edge LE of the thin aerofoil, like aerofoils 5c, 5c’ in Fig. 1. Alternatively, the shape of the aerofoils can be thick aerofoils.

[0074] The inlet gap width IGW is defined as the width at the smallest distance between the first aerofoil assembly and the second aerofoil assembly near the inlet gap IG while the outlet gap width OGW is defined as the width at the smallest distance between the first aerofoil assembly and the second aerofoil assembly near the outlet gap OG, as shown in Fig. 14.

[0075] The assembly camber line ACAL of each of the first aerofoil assembly 3 and the second aerofoil assembly 4 is connecting the leading edge LE of the front aerofoil 5a, 5a’ nearest the inlet gap IG with the trailing edges TE of each of the aerofoils in the aerofoil assembly from the front aerofoil 5a and 5a’ towards the back aerofoil 5b, 5b’ nearest an outlet gap OG of the blade assembly. The chord line ACHL of each of the first aerofoil assembly and second aerofoil assembly is connecting the leading edge LE of the front aerofoil 5a and 5a’ of the assembly with the trailing edge TE of the back aerofoil 5b and 5b’ of the assembly. The assembly camber line ACAL deviates from the assembly chord line ACHL in a direction with a component away from the central plane CP. The assembly camber line ACAL and the assembly chord line ACHL are defined according to Fig. 11.

[0076] The aerofoils of the first aerofoil assembly 3 and of the second aerofoil assembly 4 are arranged in an overlapping sequence so that one or more flow channels FC are formed between neighbouring aerofoils. The length of the flow channel FL between neighbouring aerofoils, as shown in Fig. 13, corresponds to the overlap of the two neighbouring aerofoils and is measured along the chord line CHL of the one of the two neighbouring aerofoils that is closest to the inlet gap IG of the blade assembly 1. The width FW of the flow channel FC, as shown in Fig. 12, is measured perpendicular to the chord line CHL of the one of the two neighbouring aerofoils that is closest to the inlet gap IG of the blade assembly 1. The flow channels FC are converging towards the trailing edge TE so that the inlet of the flow channel FWin is wider than the outlet of the flow channel FWout.

[0077] The smallest distance Dmin and the largest distance Dmax from the central longitudinal axis 7 and the outer surface of any of the at least two aerofoils of the first aerofoil assembly and the at least two aerofoils of the second aerofoil assembly is defined in Fig. 13. The lateral length of the blade assembly LI is the maximum projected length on the central plane CP of the first aerofoil assembly 3 and the second aerofoil assembly 4, and the maximal width MW of the blade assembly 1 is the largest distance perpendicularly to the central plane CP between outer surfaces of the first aerofoil assembly 3 and the second aerofoil assembly 4, as shown in Fig. 14.

[0078] An example of streamlines of an incoming airflow through a cross section of the first embodiment of the blade assembly is shown in Fig. 8 based on a simulation. The orientation of the blade assembly 1 with respect to the direction of the incoming airflow, i.e. the apparent wind, with an angle to the central plane CP of the blade assembly 1 gives rise to a pressure side and a suction side of the blade assembly 1 providing a lift force on the blade assembly 1, which will contribute to the propulsion for a ship 2. In the simulation shown in Fig. 8, the incoming airflow has an angle of 10° to the central plane CP of the blade assembly 1 and it is clearly seen how the airflow is accelerated above the blade assembly 1 and creating a low pressure on a suction side above the first aerofoil assembly 3 due to the acceleration of the flow. The short distance between neighbouring streamlines in this area indicates the high speed of the airflow and the corresponding low pressure. On the other side of the blade assembly 1, below the second aerofoil assembly 4, the speed of the airflow is lower than the speed of the free airflow, indicated by the larger distance between neighbouring streamlines, and a corresponding higher pressure, thus this side constitutes the pressure side of the blade assembly 1.

[0079] Most of the airflow entering through the inlet gap IG passes out from the interior of the blade assembly 1 through the flow channels FC of the first aerofoil assembly 3, which generates high-speed air injection and thereby kinetic energy into the boundary layer of the airflow at the suction side of the blade assembly 1, thus preventing the formation of flow separation at the suction side of the blade assembly 1 and the drop in lift force caused by flow separation.

[0080] Thus, the flow channels FC provide for aerofoil assemblies 3, 4 with a highly convex shape, wherein the assembly camber line ACAL deviates significantly from the assembly chord line ACHL and therefore have a high lift coefficient without being prone to flow separation or stall. This means that the wind propulsion force that can be achieved from a given circular area of the ship’s deck by a wind assisted ship propulsion arrangement can be increased or even maximised by use of the blade assembly 1 according to the present disclosure.

[0081] The provision of the flow blocking arrangement 10 in the form of the movable wing element 11 and the stationary barrier 13 promotes that the flow of air incoming through the inlet gap IG will pass out through the flow channels FC of the first aerofoil assembly 3 and reduces or prevents the formation of vortices and instability in the cavity between the first and second aerofoil assemblies 3, 4. The guide vanes 14 near the leading edge of the movable wing element 11 prevents separation of the flow around the leading edge of the movable wing element 11, which also may cause formation of vortices and instability of the flow.

[0082] Fig. 9 and 10 show the longitudinal extend L2 of a blade assembly 1 that is coupled to a part of a ship 2. The first and second aerofoil assembly 3, 4 are connected by at least one support structure 6 that extends in a horizontal plane of the blade assembly and is rigidly connected to each of the aerofoils of the first and the second aerofoil assembly 3, 4 as well as to the stationary barrier 13. The support structures 6 enhance the mechanical stability of the blade assembly 1 by rigidly connecting each of the aerofoils of the two aerofoil assemblies 3, 4. As part of a support structure 6 arranged at the top end of the blade assembly 1, a flow limiting structure 106 is placed on the top of the blade assembly 1 and extends in the horizontal plane of the blade assembly 1 beyond the first aerofoil assembly 3 and the second aerofoil assembly 4 in a direction away from the central plane CP of the blade assembly 1 in order to reduce the tip effect, i.e. the flow of air around the tip of the blade assembly 1 from the pressure side to the suction side of the blade assembly 1, which reduces the efficiency of the blade assembly 1 as a means of propulsion. The flow limiting structure 106 extends 0.3 times the lateral length of the blade assembly beyond the first aerofoil assembly 3 as well as the second aerofoil assembly 4 in the direction away from the central plane CP of the blade assembly 1 at the position of the maximal width MW of the blade assembly.

[0083] Fig. 15 shows a cross-section of embodiments of a blade assembly 1, where the front aerofoils 5a, 5a’, the back aerofoils 5b, 5b’ and the intermediate aerofoils 5c, 5c’ comprise vortex generators 16. The vortex generators can be placed on all aerofoils as shown in Fig. 15 or on the front aerofoils 5a, 5a’ as shown in Fig. 16. The vortex generators 16 can be used to delay flow separation and can be advantageously placed on the front aerofoils 5a, 5a’, for delaying flow separation at places with larger angles of attack, such as close to the leading edge LE of the front aerofoils 5a, 5a’.

[0084] Fig. 15 shows a cross-section of embodiments of a blade assembly 1, where the flow blocking arrangement 10 comprises vortex generators 16. The vortex generators can be placed on the movable wing element 11 and on the stationary barrier 13 as shown in Fig. 15 or on the movable wing element 11 as shown in Fig. 16. The vortex generators 16 can be used to delay flow separation and can be advantageously placed on the movable wing element 11 for delaying flow separation at places with larger angles of attack, such as close to the front side of the movable wing element 11.

[0085] The vortex generators 16 can have a triangular shape as shown in Fig. 15 and 16. They can extend over a length VL of up to 0. 1 times of the longest chord length CL of any of the aerofoils and can extend over a height VH from the outer surface of the aerofoils or of the flow blocking arrangement by up to 0.05 times of the longest chord length CL of any of the aerofoils, as shown in the zoomed in area of Fig. 16.

[0086] The vortex generators 16 can be placed along longitudinal extend L2 of a blade assembly 1, as shown in Fig. 9b, for vortex generators 16 placed on the front aerofoils 5a’ and 5a (not shown in the figures) and on the movable wing element 11. The vortex generators 16 can be placed with different orientations, such as alternating between pointing towards the top end part and towards the lower end part of the blade assembly 1.

[0087] Embodiments according to the second aspect of the present disclosure are shown in Figs. 17- 20. A cross-section of a first embodiment of a blade assembly 1 according to the second aspect is shown in Fig. 17, comprising a first aerofoil assembly 3 and a second aerofoil assembly 4, which are mutually symmetrical around the central plane CP of the blade assembly, in which the lateral length LI of the blade assembly 1 extends. Each of the first aerofoil assembly 3 and the second aerofoil assembly 4 comprising at least two aerofoils, where the front aerofoil 5a, 5a’ and the back aerofoil 5b, 5b’ and the potentially intermediate aerofoils 5c, 5c’ are oriented with a leading edge LE of the aerofoil towards an inlet gap IG of the blade assembly between the first aerofoil assembly 3 and the second aerofoil assembly 4 and arranged in an overlapping sequence so that flow channels FC are formed between neighbouring aerofoils. Each of the front aerofoils 5a, 5a’, back aerofoils 5b, 5b’ and intermediate aerofoils 5c, 5c’ are non-symmetric aerofoils, with the camber line CAL deviating from the chord line CHL in the direction away from the central plane CP. The chord length CL from the leading edge LE to the trailing edge TE is indicated on Fig. 1 for one aerofoil 5a’ .

[0088] The blade assembly 1 in Fig. 17 is provided with a stationary barrier 13 extending from the pivot axis 12 towards the outlet gap OG of the blade assembly 1, the stationary barrier 13 being arranged symmetrically around and extending along the central plane CP of the blade assembly 1. Barrier flow channels FCB are formed between the sides of the stationary barrier 13 and the back aerofoils 5b, 5b’ having generally the same characteristics as the flow channels FC formed between neighbouring aerofoils.

[0089] When the blade assembly 1 of Fig. 17 is in operation for providing propulsion of a ship, the blade assembly 1 is rotated about the central longitudinal axis 7 by means of a yaw drive 8 so that the apparent wind encounters the blade assembly 1 at an attack angle that provides the optimal propulsion for the ship 2 on which it is arranged. When the apparent wind is incoming from the port side of the ship 2, the blade assembly is turned to a position, where the flow of air coming from the inlet gap IG mainly goes out through the flow channels FC, FCB of the first aerofoil assembly 3 while the design of the blade assembly 1 and the stationary barrier 13 allows a limited amount of the flow of air to pass the flow channels FC, FCM of the second aerofoil assembly 4. When the apparent wind has an incoming direction from starboard of the ship 2, i.e. from the right hand side of the ship 2 when facing the front of the ship 2, the blade assembly 1 is turned by the yaw drive 8 to a different position, where the flow of air coming from the inlet gap IG mainly goes out through the flow channels FC, FCB of the second aerofoil assembly 4.

[0090] The blade assembly 1 shown in cross-section in Fig. 18 of a second embodiment of the second aspect of the disclosure has a stationary barrier 13 of a substantially circular outer cross-sectional shape that does not enclose the central longitudinal axis 7 of the blade assembly 1.

[0091] The blade assembly 1 of a third embodiment is shown in cross-section in Fig. 19 has a stationary barrier 13 of a longer extent in the direction of the central plane CP of the blade assembly 1 that the embodiment shown in Fig. 17. A further embodiment of a blade assembly 1 of the second aspect of the disclosure is shown in cross-section in Fig. 20, where the front aerofoils 5a, 5a’, the back aerofoils 5b, 5b’ and the intermediate aerofoils 5c, 5c’ comprise vortex generators 16. The vortex generators can be placed on all aerofoils as shown in Fig. 15 or on the front aerofoils 5a, 5a’ only. The vortex generators 16 can be used to delay flow separation and can be advantageously placed on the front aerofoils 5a, 5a’, for delaying flow separation at places with larger angles of attack, such as close to the leading edge LE of the front aerofoils 5a, 5a’.

[0092] The flow blocking arrangement 10 is also shown to comprise vortex generators 16 on the stationary barrier 13 in order to delay of prevent flow separation from the surface of the stationary barrier 13, and the effect of the vortex generators 16 may enable the blade assembly 1 to operate at a higher angle of attack between the apparent wind and the central plane of the blade assembly 1.

[0093] A ship 2 can comprise one or more blade assemblies 1 and is further equipped with one or more yaw drives 8 which are coupled to the one or more blade assemblies 1 as shown in Fig. 21. The yaw drive 8 is used to adjust the angle of each of the one or more blade assemblies 1 by rotating the blade assembly 1 around the central longitudinal axis 7 of the blade assembly 1. A controller 9 is used for controlling the yaw drive(s) 8 of the ship 2, the controller being arranged to receive data indicative of apparent wind speed and direction and control the angle of the blade assembly with respect to the longitudinal axis of the ship accordingly by operating the yaw drive(s) in response to received data on wind direction or velocity. In case the apparent wind speed exceeds an upper safety limit, the yaw drive 8 may be operated to reduce the aerodynamical load on the blade assembly, such as by rotating the blade assembly 1 to a position, where the outlet gap OG is oriented in the direction of the apparent wind. The ship 2 is optionally furthermore provided with one or more wing drives 15 which are coupled to the one or more blade assemblies 1 as shown in Fig. 21 for rotating the movable wing elements 11 of the one or more blade assemblies 1. The controller 9 is arranged for controlling the operation of the wing drives 15. List of references

[0094] 1 Blade assembly

[0095] 2 Ship

[0096] 3 First aerofoil assembly

[0097] 4 Second aerofoil assembly

[0098] 5a Front aerofoil in the first aerofoil assembly of a first embodiment of a blade assembly

[0099] 5a’ Front aerofoil in the second aerofoil assembly of a first embodiment of a blade assembly

[0100] 5b Back aerofoil in the first aerofoil assembly of a first embodiment of a blade assembly

[0101] 5b’ Back aerofoil in the second aerofoil assembly of a first embodiment of a blade assembly

[0102] 5c Intermediate aerofoil(s) in the first aerofoil assembly of a first embodiment of a blade assembly

[0103] 5c’ Intermediate aerofoil(s) in the second aerofoil assembly of a first embodiment of a blade assembly

[0104] 6 Support structure

[0105] 7 Central longitudinal axis

[0106] 8 Yaw drive

[0107] 9 Controller

[0108] 10 Flow blocking arrangement

[0109] 11 Movable wing element

[0110] 12 Pivot axis

[0111] 13 Stationary barrier

[0112] 14 Guide vanes

[0113] 15 Wing drive

[0114] 16 Vortex generator

[0115] 105a Front aerofoil in the first aerofoil assembly of other embodiments of a blade assembly

[0116] 105a’ Front aerofoil in the second aerofoil assembly of other embodiments of a blade assembly

[0117] 105b Back aerofoil in the first aerofoil assembly of other embodiments of a blade assembly 105b’ Back aerofoil in the second aerofoil assembly of other embodiments of a blade assembly 105c Intermediate aerofoil(s) in the first aerofoil assembly of other embodiments of a blade assembly

[0118] 105c’ Intermediate aerofoil(s) in the second aerofoil assembly of other embodiments of a blade assembly

[0119] 106 Flow limiting structure

[0120] ACAL Assembly camber line

[0121] ACHL Assembly chord line

[0122] CAL Camber line of an aerofoil

[0123] CE Cylindrical element of thin aerofoil

[0124] CHL Chord line of an aerofoil

[0125] CL Chord length

[0126] CP Central plane

[0127] Dmin Smallest distance from central longitudinal axis to the outer surface of an aerofoil

[0128] Dmax Largest distance from central longitudinal axis to the outer surface of an aerofoil

[0129] FC Flow channels

[0130] FCB Barrier flow channels between the stationary barrier and the back aerofoils

[0131] FL Flow channel length

[0132] FW Flow channel width

[0133] FWin Flow channel width, inlet

[0134] FWout Flow channel width, outlet

[0135] IG Inlet gap

[0136] IGW Inlet gap width

[0137] LI Lateral length of the cross-section of the blade assembly

[0138] L2 Longitudinal extent of the blade assembly

[0139] LE Leading edge of aerofoil

[0140] MW Maximal width of the blade assembly perpendicularly to the central plane

[0141] OG Outlet gap

[0142] OGW Outlet gap width

[0143] TE Trailing edge of aerofoil

[0144] VL length of vortex generator

[0145] VH height of vortex generator Items

[0146] 1. A blade assembly for providing wind propulsion for a ship, the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship, and a first aerofoil assembly and a second aerofoil assembly, each of the first aerofoil assembly and the second aerofoil assembly comprising at least two aerofoils, wherein the first aerofoil assembly is arranged at one side of a central plane of the blade assembly, the central plane extending between the top end part and the lower end part and encompassing a central longitudinal axis of the blade assembly, and the second aerofoil assembly is arranged at the opposite side of the central plane than the first aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are oriented with a leading edge of the aerofoil towards an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils, and wherein for each of the first aerofoil assembly and the second aerofoil assembly an assembly camber line connecting the leading edge of the front aerofoil nearest the inlet gap with the trailing edges of each of the aerofoils in the aerofoil assembly from the front aerofoil towards the back aerofoil nearest an outlet gap of the blade assembly deviates from an assembly chord line connecting the leading edge of the front aerofoil with the trailing edge of the back aerofoil in a direction with a component away from the central plane, the blade assembly further comprising a flow blocking arrangement which can be selectively shifted between a first position, where flow of air from the inlet gap and out through the flow channel(s) of the first aerofoil assembly is limited, and a second position, where flow of air from the inlet gap and out through the flow channel(s) of the second aerofoil assembly is limited. 2. The blade assembly according to item 1, wherein the flow blocking arrangement comprises a movable wing element extending in the longitudinal direction of the blade assembly.

[0147] 3. The blade assembly according to item 2, wherein the wing element is arranged to pivot around a pivot axis extending in the longitudinal direction of the blade assembly.

[0148] 4. The blade assembly according to item 3, wherein the pivot axis extends along the central plane of the blade assembly between the central longitudinal axis of the blade assembly and an outlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly.

[0149] 5. The blade assembly according to item 3, wherein the pivot axis extends along the central plane of the blade assembly between the central longitudinal axis of the blade assembly and an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly.

[0150] 6. The blade assembly according to any of item 2 to 5, wherein the flow blocking arrangement further comprises a stationary barrier extending between the movable wing element and an outlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly.

[0151] 7. The blade assembly according to any of item 2 to 6, wherein the flow blocking arrangement further comprises guide vanes near the leading edge of the movable wing element, the guide vanes being movable together with the movable wing element, the guide vanes being provided to decrease the separation of flow near the leading edge of the movable wing element, when the flow comes from the inlet gap of the blade assembly.

[0152] 8. A blade assembly for providing wind propulsion for a ship, the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship, and a first aerofoil assembly and a second aerofoil assembly, each of the first aerofoil assembly and the second aerofoil assembly comprising at least two aerofoils, wherein the first aerofoil assembly is arranged at one side of a central plane of the blade assembly, the central plane extending between the top end part and the lower end part of the blade assembly and encompassing a central longitudinal axis of the blade assembly, and the second aerofoil assembly is arranged at the opposite side of the central plane than the first aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are oriented with a leading edge of the aerofoil towards an inlet gap of the blade assembly between the first aerofoil assembly and the second aerofoil assembly, wherein the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly are arranged in an overlapping sequence so that one or more flow channels are formed between neighbouring aerofoils, and wherein for each of the first aerofoil assembly and the second aerofoil assembly an assembly camber line connecting the leading edge of the front aerofoil nearest the inlet gap with the trailing edges of each of the aerofoils in the aerofoil assembly from the front aerofoil towards the back aerofoil nearest an outlet gap of the blade assembly deviates from an assembly chord line (ACHL) connecting the leading edge (LE) of the front aerofoil with the trailing edge of the back aerofoil in a direction with a component away from the central plane, the blade assembly further comprising a stationary barrier extending between the first aerofoil assembly and the second aerofoil assembly and forming barrier flow channels between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly, respectively.

[0153] 9. The blade assembly according to any of items 6 to 8, wherein the stationary barrier is arranged symmetrically around and extending along the central plane of the blade assembly.

[0154] 10. The blade assembly according to any of items 6 to 9, wherein the central longitudinal axis extends within the stationary barrier.

[0155] 11. The blade assembly according to any of items 6 to 10, wherein the barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are of a width of at least 0.01 times of the chord length of the respective back aerofoil, the extent being measured in the direction perpendicular to the chord line of the respective back aerofoil, such as in the range of 0.01 to 0.4 time the chord length, preferably within 0.05 to 0.4 times the chord length.

[0156] 12. The blade assembly according to any of items 6 to 11, wherein the barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are of an extent of at least 0.02 times of the chord length of the respective back aerofoil, the extent being measured in the direction of the chord line of the respective back aerofoil, such as in the range of 0.02 to 0.8 time the chord length, preferably within 0.1 to 0.5 times the chord length.

[0157] 13. The blade assembly according to any of times 6 to 12, wherein the barrier flow channels formed between the stationary barrier and the back aerofoil of the first aerofoil assembly and of the second aerofoil assembly are converging towards the trailing edge of the back aerofoils, such as by at least 0.1 times the width of the flow channel from an inlet of the flow channel to an outlet of the flow channel, such as in the range of 0. 1 to 0.9 times the width, preferably within the range of 0.2 to 0.5 times the width.

[0158] 14. The blade assembly according to any of the preceding items, wherein at least one support structure is provided connecting each of the at least two aerofoils of each of the first aerofoil assembly and the second aerofoil assembly at a position between the top end part and the lower end part of the blade assembly and optionally also a stationary barrier of the blade assembly at a position between the top end part and the lower end part of the blade assembly.

[0159] 15. The blade assembly according to item 14, wherein at least one of such support structures is positioned at least 1 / 3 of the longitudinal extent of the blade assembly from the lower end part of the blade assembly (1).

[0160] 16. The blade assembly according to any of the preceding items, wherein the maximal width of the blade assembly perpendicularly to the central plane constitutes at least 0.4 times the lateral length of the blade assembly, such as at least 0.6 times the lateral length of the blade assembly, preferably in the range of 0.8 to 1.2 times the lateral length of the blade assembly, the lateral length of the blade assembly being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, and the maximal width of the blade assembly is the largest distance perpendicularly to the central plane between outer surfaces of the first aerofoil assembly and the second aerofoil assembly.

[0161] 17. The blade assembly according to any of the preceding items, wherein the smallest distance from the central longitudinal axis to the outer surface of any of the at least two aerofoils of the first aerofoil assembly and the second aerofoil assembly is at least 40% of the largest distance from the central longitudinal axis to the outer surface of any of the at least two aerofoils of the first aerofoil assembly and the second aerofoil assembly, preferably at least 60% of the largest distance, and more preferred at least 80% of the largest distance.

[0162] 18. The blade assembly according to any of the preceding items, wherein the flow channels between any two neighbouring aerofoils of the first aerofoil assembly and of the second aerofoil assembly is of an extent of at least 0.02 times of the chord length of that of the two aerofoils closest to the inlet gap of the blade assembly, the extent being measured in the direction of the chord line of that aerofoil, such as in the range of 0.02 to 0.8 time the chord length, preferably within 0.1 to 0.5 times the chord length.

[0163] 19. The blade assembly according to any of the preceding items, wherein the flow channels between any two neighbouring aerofoils of the first aerofoil assembly and of the second aerofoil assembly are of a width of at least 0.01 times of the chord length of that of the two aerofoils closest to the inlet gap of the blade assembly, the extent being measured in the direction perpendicular to the chord line of that aerofoil, such as in the range of 0.01 to 0.4 time the chord length, preferably within 0.05 to 0.4 times the chord length.

[0164] 20. The blade assembly according to any of the preceding items, wherein at least one of the flow channels between neighbouring aerofoils of the first aerofoil assembly and the second aerofoil assembly, preferably all of the flow channels between neighbouring aerofoils of the first aerofoil assembly and the second aerofoil assembly, are converging towards the trailing edge of the neighbouring aerofoils, such as by at least 0. 1 times the width of the flow channel from an inlet of the flow channel to an outlet of the flow channel, such as in the range of 0. 1 to 0.9 times the width at the inlet of the flow channel, preferably within the range of 0.2 to 0.5 times the width at the inlet of the flow channel. 21. The blade assembly according to any of the preceding items, wherein the first aerofoil assembly is symmetrical with the second aerofoil assembly about the central plane of the blade assembly.

[0165] 22. The blade assembly according to any of the preceding items, wherein the width of the inlet gap being the smallest distance between the first aerofoil assembly and the second aerofoil assembly near the inlet gap is at least 0.1 times the lateral length of the blade assembly, the lateral length being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, such as within the range of 0.1 to 0.8 times the lateral length of the blade assembly, preferably within the range of 0.3 to 0.6 times the lateral length of the blade assembly.

[0166] 23. The blade assembly according to any of the preceding items, wherein the width of the outlet gap being the smallest distance between the first aerofoil assembly and the second aerofoil assembly near the outlet gap is at least 0.01 times the lateral length of the blade assembly, the lateral length being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, such as within the range of 0.01 to 0.2 times the lateral length of the blade assembly, preferably within the range of 0.05 to 0.15 times the lateral length of the blade assembly.

[0167] 24. The blade assembly according to any of the preceding items, wherein the longitudinal extent of the blade assembly is more than 20 meter, such as more than 30 meter, in particular in the range of 20 to 80 meter, such as in the range of 30 to 60 meter or in the range of 20 to 30 meter.

[0168] 25. The blade assembly according to any of the preceding items, wherein a flow limiting structure is provided at the top end part of the blade assembly, the flow limiting structure extending at least 0.1 time the lateral length of the blade assembly beyond the first aerofoil assembly and the second aerofoil assembly in a direction away from the central plane of the blade assembly at the position of the maximal width of the blade assembly, the lateral length of the blade assembly being the maximum projected length on the central plane of the first aerofoil assembly and the second aerofoil assembly, and the maximal width of the blade assembly is the largest distance perpendicularly to the central plane between outer surfaces of the first aerofoil assembly and the second aerofoil assembly, such as in the range of 0.1 to 0.75 times the lateral length of the blade assembly, preferably in the range of 0.2 to 0.5 times the lateral length of the blade assembly.

[0169] 26. The blade assembly according to item 25, wherein the flow limiting structure constitutes at least one of the support structures of the blade assembly.

[0170] 27. The blade assembly according to any of the preceding items, wherein at least one of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly further comprise one or more vortex generators on the outer surface of the aerofoils.

[0171] 28. The blade assembly according to item 27, wherein the one or more vortex generators are placed on the outer surface of the front aerofoil of each of the first aerofoil assembly and the second aerofoil assembly.

[0172] 29. The blade assembly according to any of the preceding items, wherein the flow blocking arrangement further comprises one or more vortex generators.

[0173] 30. The blade assembly according to items 2 and 29, wherein the one or more vortex generators are placed on the movable wing element.

[0174] 31. The blade assembly according to any of items 27 to 30, wherein the one or more vortex generators extend over a length of up to 0. 1 times of the longest chord length of any of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly.

[0175] 32. The blade assembly according to claims 27 to 31, wherein the one or more vortex generators extend over a height from the outer surface of the aerofoils or from the flow blocking arrangement by up to 0.05 times of the longest chord length of any of the aerofoils of each of the first aerofoil assembly and the second aerofoil assembly.

[0176] 33. A ship comprising at least one blade assembly according to any of items 1 to 32, wherein each blade assembly is coupled to a yaw drive for adjusting the angle of the blade assembly with respect to a longitudinal axis of the ship. 34. The ship according to item 33, wherein the yaw drive is arranged to rotate the blade assembly around the central longitudinal axis of the blade assembly.

[0177] 35. The ship according to item 33 or 34 further comprising a controller for controlling the yaw drive(s) of the ship, the controller being arranged to receive data indicative of wind direction and control the angle of the blade assembly with respect to the longitudinal axis of the ship accordingly by operating the yaw drive(s) in response to received data on wind direction. 36. The ship according to item 35, wherein the controller furthermore is arranged to control the shifting of the flow blocking arrangement between the first position and the second position of the flow blocking arrangement in response to received data on wind direction.

Claims

1. 32Claims1. A blade assembly (1) for providing wind propulsion for a ship (2), the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship (2), and a first aerofoil assembly (3) and a second aerofoil assembly (4), each of the first aerofoil assembly (3) and the second aerofoil assembly (4) comprising at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’), wherein the first aerofoil assembly (3) is arranged at one side of a central plane (CP) of the blade assembly (1), the central plane (CP) extending between the top end part and the lower end part of the blade assembly (1) and encompassing a central longitudinal axis (7) of the blade assembly (1), and the second aerofoil assembly (4) is arranged at the opposite side of the central plane (CP) than the first aerofoil assembly (3), wherein the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) are oriented with a leading edge (LE) of the aerofoil (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) towards an inlet gap (IG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4), wherein the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) are arranged in an overlapping sequence so that one or more flow channels (FC) are formed between neighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’), and wherein for each of the first aerofoil assembly (3) and the second aerofoil assembly (4) an assembly camber line (ACAL) connecting the leading edge (LE) of the front aerofoil (5a, 5a’, 105a, 105a’) nearest the inlet gap (IG) with the trailing edges (TE) of each of the aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) in the aerofoil assembly (3, 4) from the front aerofoil (5a, 5a’, 105a, 105a’) towards the back aerofoil (5b, 5b’, 105b, 105b’) nearest an outlet gap (OG) of the blade assembly (1) deviates from an assembly chord line (ACHL) connecting the leading edge (LE) of the front aerofoil (5a, 5a’, 105a, 105a’) with the trailing edge (TE) of the back aerofoil (5b, 5b’, 105b, 105b’) in a direction with a component away from the central plane (CP),33 the blade assembly (1) further comprising a flow blocking arrangement (10, 11, 13, 14) which can be selectively shifted between a first position, where flow of air from the inlet gap (IG) and out through the flow channel(s) (FC) of the first aerofoil assembly (3) is limited, and a second position, where flow of air from the inlet gap (IG) and out through the flow channel(s) (FC) of the second aerofoil assembly (4) is limited.

2. The blade assembly (1) according to claim 1, wherein the flow blocking arrangement (10,11, 13, 14) comprises a movable wing element (11) extending in the longitudinal direction of the blade assembly (1).

3. The blade assembly (1) according to claim 2, wherein the wing element (11) is arranged to pivot around a pivot axis (12) extending in the longitudinal direction of the blade assembly.

4. The blade assembly (1) according to claim 3, wherein the pivot axis (12) extends along the central plane (CP) of the blade assembly (1) between the central longitudinal axis (7) of the blade assembly (1) and an outlet gap (OG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4).

5. The blade assembly (1) according to claim 3, wherein the pivot axis (12) extends along the central plane (CP) of the blade assembly (1) between the central longitudinal axis (7) of the blade assembly (1) and an inlet gap (IG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4).

6. The blade assembly (1) according to any of claim 2 to 5, wherein the flow blocking arrangement (10, 11, 13, 14) further comprises a stationary barrier (13) extending between the movable wing element (11) and an outlet gap (OG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4).

7. The blade assembly (1) according to any of claim 2 to 6, wherein the flow blocking arrangement (10, 11, 13, 14) further comprises guide vanes (14) near the leading edge (LE) of the movable wing element (11), the guide vanes (14) being movable together with the movable wing element (11), the guide vanes (14) being provided to decrease the separationof flow near the leading edge (LE) of the movable wing element (11), when the flow comes from the inlet gap (IG) of the blade assembly (1).

8. The blade assembly (1) according to any of the preceding claims, wherein at least one support structure (6) is provided connecting each of the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) at a position between the top end part and the lower end part of the blade assembly (1).

9. The blade assembly (1) according to any of the preceding claims, wherein the maximal width (MW) of the blade assembly (1) perpendicularly to the central plane (CP) constitutes at least 0.4 times the lateral length (LI) of the blade assembly (1), such as at least 0.6 times the lateral length (LI) of the blade assembly (1), preferably in the range of 0.8 to 1.2 times the lateral length (LI) of the blade assembly (1), the lateral length (LI) of the blade assembly (1) being the maximum projected length on the central plane (CP) of the first aerofoil assembly (3) and the second aerofoil assembly (4), and the maximal width (MW) of the blade assembly (1) is the largest distance perpendicularly to the central plane (CP) between outer surfaces of the first aerofoil assembly (3) and the second aerofoil assembly (4).

10. The blade assembly (1) according to any of the preceding claims, wherein the flow channels (PC) between any two neighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of the first aerofoil assembly (3) and of the second aerofoil assembly (4) are of a width of at least 0.01 times of the chord length (CL) of that of the two aerofoils (5a, 5a’, 5c, 5c’, 105a, 105a’, 105c, 105c’) closest to the inlet gap (IG) of the blade assembly (1), the extent being measured in the direction perpendicular to the chord line (CL) of that aerofoil (5a, 5a’, 5c, 5c’, 105a, 105a’, 105c, 105c’), such as in the range of 0.01 to 0.4 time the chord length (CL), preferably within 0.05 to 0.4 times the chord length (CL).

11. The blade assembly (1) according to any of the preceding claims, wherein at least one of the flow channels (FC) between neighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of the first aerofoil assembly (3) and the second aerofoil assembly (4), preferably all of the flow channels (FC) between neighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of the first aerofoil assembly (3) and the second aerofoil assembly (4), are converging towards the trailing edge (TE) of theneighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’), such as by at least 0. 1 times the width of the flow channel (FW) from an inlet of the flow channel (FC) to an outlet of the flow channel (FC), such as in the range of 0. 1 to 0.9 times the width (FWin), preferably within the range of 0.2 to 0.5 times the width (FWin).

12. A ship (2) comprising at least one blade assembly (1) according to any of claims 1 to 11, wherein each blade assembly (1) is coupled to a yaw drive (8) for adjusting the angle of the blade assembly (1) with respect to a longitudinal axis of the ship (2).

13. The ship (2) according to claim 12, wherein the yaw drive (8) is arranged to rotate the blade assembly (1) around the central longitudinal axis (7) of the blade assembly (1).

14. The ship (2) according to claim 12 or 13, further comprising a controller (9) for controlling the yaw drive(s) (8) of the ship (2), the controller (9) being arranged to receive data indicative of wind direction and control the angle of the blade assembly (1) with respect to the longitudinal axis of the ship (2) accordingly by operating the yaw drive(s) (8) in response to received data on wind direction.

15. The ship (2) according to claim 14, wherein the controller (9) furthermore is arranged to control the shifting of the flow blocking arrangement (10, 11, 13, 14) between the first position and the second position of the flow blocking arrangement (10, 11, 13, 14) in response to received data on wind direction.

16. A blade assembly (1) for providing wind propulsion for a ship (2), the blade assembly comprising a top end part and a lower end part for being coupled to a part of the ship (2), and a first aerofoil assembly (3) and a second aerofoil assembly (4), each of the first aerofoil assembly (3) and the second aerofoil assembly (4) comprising at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’), wherein the first aerofoil assembly (3) is arranged at one side of a central plane (CP) of the blade assembly (1), the central plane (CP) extending between the top end part and the lower end part of the blade assembly (1) and encompassing a central longitudinal axis (7) of the blade assembly (1), and the second aerofoil assembly (4) is arranged at the opposite side of the central plane (CP) than the first aerofoil assembly (3),36 wherein the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) are oriented with a leading edge (LE) of the aerofoil (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) towards an inlet gap (IG) of the blade assembly (1) between the first aerofoil assembly (3) and the second aerofoil assembly (4), wherein the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) are arranged in an overlapping sequence so that one or more flow channels (FC) are formed between neighbouring aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’), and wherein for each of the first aerofoil assembly (3) and the second aerofoil assembly (4) an assembly camber line (ACAL) connecting the leading edge (LE) of the front aerofoil (5a, 5a’, 105a, 105a’) nearest the inlet gap (IG) with the trailing edges (TE) of each of the aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) in the aerofoil assembly (3, 4) from the front aerofoil (5a, 5a’, 105a, 105a’) towards the back aerofoil (5b, 5b’, 105b, 105b’) nearest an outlet gap (OG) of the blade assembly (1) deviates from an assembly chord line (ACHL) connecting the leading edge (LE) of the front aerofoil (5a, 5a’, 105a, 105a’) with the trailing edge (TE) of the back aerofoil (5b, 5b’, 105b, 105b’) in a direction with a component away from the central plane (CP), the blade assembly (1) further comprising a stationary barrier (13) extending between the first aerofoil assembly (3) and the second aerofoil assembly (4) and forming barrier flow channels (FCB) between the stationary barrier (13) and the back aerofoil (5b, 5b’, 105b, 105b’) of the first aerofoil assembly (3) and of the second aerofoil assembly (4), respectively.

17. The blade assembly (1) according to claim 16, wherein the stationary barrier (13) is arranged symmetrically around and extending along the central plane (CP) of the blade assembly (1).3718. The blade assembly (1) according to claim 16 or 17, wherein the central longitudinal axis (7) extends within the stationary barrier (13).

19. The blade assembly (1) according to any of claims 16 to 18, wherein the flow channels (FCB) formed between the stationary barrier (13) and the back aerofoil (5b, 5b’, 105b, 105b’) of the first aerofoil assembly (3) and of the second aerofoil assembly (4) are of a width of at least 0.01 times of the chord length (CL) of the respective back aerofoil (5b, 5b’, 105b, 105b’), the extent being measured in the direction perpendicular to the chord line (CL) of the respective back aerofoil (5b, 5b’, 105b, 105b’), such as in the range of 0.01 to 0.4 time the chord length (CL), preferably within 0.05 to 0.4 times the chord length (CL).

20. The blade assembly (1) according to any of the claims 16 to 19, wherein the barrier flow channels (FCB) formed between the stationary barrier (13) and the back aerofoil (5b, 5b’, 105b, 105b’) of the first aerofoil assembly (3) and of the second aerofoil assembly (4) are converging towards the trailing edge (TE) of the back aerofoils (5b, 5b’, 105b, 105b’), such as by at least 0.1 times the width of the flow channel (FW) from an inlet of the flow channel (FCB) to an outlet of the flow channel (FCB), such as in the range of 0.1 to 0.9 times the width (FWin), preferably within the range of 0.2 to 0.5 times the width (FWin).

21. The blade assembly (1) according to any of claims 16-20, wherein at least one support structure (6) is provided connecting each of the at least two aerofoils (5a, 5a’, 5b, 5b’, 5c, 5c’, 105a, 105a’, 105b, 105b’, 105c, 105c’) of each of the first aerofoil assembly (3) and the second aerofoil assembly (4) as well as the stationary barrier (13) at a position between the top end part and the lower end part of the blade assembly (1).

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