Noise-optimized ducted propeller

Abstract

The invention relates to a ducted propeller (1) and to an aircraft having a ducted propeller according to the invention. The ducted propeller (1) has a stator (10) which comprises a central element (12) extending along a longitudinal axis (x). The stator (10) further has a housing (13) which is arranged around the central element (12), wherein the central element (12) is connected to the housing (13) via at least one first web (11a) and at least one second web (11b). A rotor (20) having a plurality of rotor blades (21) is arranged on the central element (12) of the stator (10).According to the invention, a first web (11a) is arranged offset from a second web (11b) axially along the longitudinal axis (x) by a defined distance (d), wherein the distance (d) is selected such that a first sound wave (4a) generated at the first web (11a) due to the air flow is 180° out of phase with a second sound wave (4b) generated at the second web (11b) due to the air flow and identical to the first sound wave (4a).

Description

[0001] The invention relates to a ducted propeller, in particular of an aircraft such as a VTOL (vertical take-off and landing) aircraft, as well as an aircraft with a ducted propeller according to the invention.

[0002] Various types of aircraft propulsion systems are known from the prior art. Compared to conventional free-running propellers, so-called ducted propellers have the advantage of reducing thrust losses due to turbulence at the rotor blade tips. For the purposes of this application, a ducted propeller is defined as a propeller, i.e., a rotor with rotor blades, enclosed by a housing. The ducted propeller can, for example, be part of an aircraft turbine assembly or be designed as a standalone propulsion system. Ducted propellers are also conceivable as part of a compressor or turbomachine independent of aircraft propulsion systems.

[0003] Such a ducted propeller 1 according to the prior art is shown in Fig. 1 in a cross-section. The ducted propeller 1 has a stator consisting of a central element 12, a cylindrical housing 13, and webs 11, wherein the webs 11 connect the central element 12 and the housing 13. The central element 12 is arranged along a longitudinal axis x of the ducted propeller 1. The longitudinal axis x runs along the flow direction of the ducted propeller 1. The flow direction is understood to be the direction in which the air is moved during regular operation of the ducted propeller 1. In Fig. 1 an air flow 2 is indicated by arrows, so that air flows from left to right through the ducted propeller 1 according to Fig. 1 flows during regular operation and consequently a force is generated by the ducted propeller 1, which points to the left in the plane of the drawing. Furthermore, a rotor 20 with corresponding rotor blades 21 is mounted on the central element 12 of the stator 10, which is designed to accelerate the air flow 2 through the ducted propeller 1. The rotor 20 is arranged upstream of the webs 11 in the flow direction, so that the air flow 2 moving through the ducted propeller 1 first passes the rotor 20 or its rotor blades 21 and then the webs 11.

[0004] Due to the rotational movement of the rotor 20, when the air accelerated by the rotor 20 hits the webs 11, a sound wave 4a, 4b is generated at a contact point 30 between the air and the web 11, which can be recorded by corresponding sensors 3. In the Fig. In the example shown in Figure 1, a first sound wave 4a and a second sound wave 4b are generated at the two illustrated webs 11. Depending on the speed of the rotor 20, the sound waves 4a, 4b have a correspondingly identical shape in terms of amplitude and frequency. If the two sound waves 4a, 4b are superimposed, a resulting sound wave 5 is even stronger in terms of amplitude, i.e., sound pressure, so that the noise is amplified.

[0005] Various objects relating to ducted propellers are known from the prior art. Document DE 692 24 853 T2 discloses an axial fan with two guide vane rings arranged axially adjacent to one another. US 2004 234 372 A1 discloses a turbomachine with a plurality of guide vanes distributed around the circumference, wherein the guide vanes vary in their axial extent and axial arrangement. Document US 2012 328 432 A1 discloses two sets of blades being arranged offset from one another in the axial direction. Document DE 100 53 361 C1 discloses a blade array arrangement for a turbomachine, wherein the blades are arranged axially offset.

[0006] Against the background of the prior art described above, the object of the present invention is to provide a ducted propeller in which noise generation can be significantly reduced. Likewise, the object of the present invention is to provide a corresponding aircraft with a ducted propeller according to the invention.

[0007] This object is achieved by the subject matter of the independent claims. Advantageous further developments of the invention are disclosed by the subject matter of the subclaims.

[0008] The ducted propeller according to the invention is intended in particular for use as a drive in an aircraft, such as a VTOL aircraft, and has a stator which comprises a central element extending along a longitudinal axis. Furthermore, the stator has a housing which is arranged around the central element, wherein the central element is connected to the housing via at least one first web and at least one second web, wherein the first web and the second web are preferably of identical construction. The webs are arranged radially distributed around the central element and thus the longitudinal axis of the ducted propeller. A rotor with a plurality of rotor blades is arranged on the central element of the stator. A plurality is understood to mean any number greater than 1. The rotor is designed to rotate about the longitudinal axis and is therefore mounted accordingly on the central element.It is further arranged upstream of the at least one first web and the at least one second web in a flow direction of the ducted propeller. According to the invention, the at least one first web is offset from the at least one second web axially along the longitudinal axis by a defined distance, wherein the distance is selected such that a first sound wave generated at the at least one first web due to the air flow is 180° out of phase with a second sound wave generated at the at least one second web due to the air flow and identical to the first sound wave. Identical sound waves are understood to be those which are indistinguishable in amplitude and frequency.

[0009] Because the sound waves are 180 degrees out of phase, a maximum of one sound wave meets a minimum of the other, canceling each other out. This creates a "noise-cancelling" effect that significantly reduces the noise generated by the ducted propeller.

[0010] The distance between the at least one first web and the at least one second web is preferably designed for a main operating speed of the rotor, so that at this speed there is a phase shift of 180 degrees. Consequently, at this rotor speed the distance between the first web and the second web is to be set to half the wavelength of the resulting sound waves. In aircraft engines, the main operating speed could, for example, be the speed set during regular cruise flight, i.e. outside of takeoff and landing. The main operating speed is to be equated with a speed for continuous operation. As a rule, technical devices such as the ducted propeller are designed for continuous operation and, associated with this, a specific speed. The distance between the at least one first web and the at least one second web is preferably in a range between 0.05 m and 0.28 m.In aircraft propulsion systems, especially VTOL aircraft, the required phase shift of the sound waves can be achieved using this distance.

[0011] In an advantageous embodiment of the invention, the ducted propeller has an even number of webs, wherein in particular half of the webs are first webs and half are second webs. In this way, a structure can be made possible in which the same number of first and second sound waves are generated, so that optimal mutual cancellation of the phase-shifted sound waves is achieved. An embodiment in which the first webs and the second webs are arranged opposite one another with respect to the central element is particularly preferred. An opposite arrangement of the webs occurs within the scope of the application when, in the circumferential direction around the longitudinal axis of the ducted propeller, two webs enclose an angle of 180 degrees. Due to the above-mentioned structure, according to which a first web is opposite another first web orIf a second web is opposite another second web, a symmetrical force distribution between the central element and the housing can be achieved, thus improving the stability of the arrangement. It is further preferred if the opposing pairs of first and second webs alternate in the circumferential direction and are evenly distributed over the circumference. Such an arrangement can achieve a particularly effective form of noise suppression.

[0012] In an advantageous embodiment of the invention, two first webs are provided, which are opposite one another with respect to the longitudinal axis, and two second webs are provided, which are arranged, in particular, offset by 90 degrees from one another in the circumferential direction around the longitudinal axis. Such an arrangement represents a good compromise between noise compensation, weight, and stability.

[0013] In a further advantageous embodiment of the invention, the first webs and / or the second webs are inclined in the direction of flow through the ducted propeller. Furthermore, the stator housing is preferably cylindrical. These corresponding measures can create particularly favorable flow behavior within the ducted propeller.

[0014] In a further advantageous embodiment of the invention, the position of the at least one first web and / or the at least one second web can be changed in the direction of the longitudinal axis, such that the distance between the at least one first web and the at least one second web can be adjusted. In this case, the at least one first web or the at least one second web is preferably movable along the longitudinal axis with respect to the housing. As a result, the distance between the webs can be adjusted accordingly to the speed of the rotor, such that the advantageous effect of the phase shift of the sound waves can be used over the widest possible speed range of the rotor. The movement can be generated, for example, by a linear drive in the central element or housing.

[0015] The aircraft according to the invention has at least one ducted propeller according to the invention.

[0016] Advantageous aspects and embodiments of the invention are explained in more detail below with reference to the accompanying figures. The figures show: Fig. 1 shows a schematic representation of a ducted propeller 1 according to the prior art and an illustration of the problem underlying the invention Fig. 2 shows a schematic representation of an embodiment of a ducted propeller 1 according to the invention and an illustration of the problem solution Fig. 3a shows a schematic representation of a second embodiment of a ducted propeller 1 according to the invention in a front view Fig. 3b shows a schematic representation of the second embodiment of a ducted propeller 1 according to the invention in a perspective view

[0017] On Fig. 1 has already been discussed in detail in the discussion of the state of the art, so that a detailed description can be omitted here.

[0018] Fig. 2 shows in contrast to Fig. 1 is a schematic representation of an embodiment of a ducted propeller 1 according to the invention. The representation corresponds to that of Fig. 1, so that the differences are clearly visible.

[0019] The ducted propeller 1 according to the invention according to Fig. 2 also has a stator 10, consisting of a housing 13, a central part 12, and webs 11a, 11b. The central part 12 and the cylindrical housing 13 are arranged along a longitudinal axis x. The rotor 20 with its rotor blades 21 is rotatably mounted on the central part 12, so that it can rotate about the longitudinal axis x. The air flow 2 is generated as in Fig. 1 from left to right in the plane of the drawing, so that the flow direction of the ducted propeller is the same as in Fig. 1 is oriented from left to right. The rotor 20 is arranged upstream of the webs 11a, 11b of the stator 10 with respect to the flow direction, so that the air flow 2 first passes the rotor 20 and then the webs 11a, 11b.

[0020] Unlike in Fig. 1, a distinction is made between a first web 11a and a second web 11b, which are preferably of identical construction. The first web 11a is arranged offset from the second web 11b in the longitudinal direction x and upstream of the flow direction by the distance d.

[0021] When the air flow 2 passes through the ducted propeller 1, a similar effect is created to the Fig. 1 a first sound wave 4a in a first contact point 30a on the first web 11a and a second sound wave 4b in a second contact point 30b on the second web 11b. These sound waves 4a, 4b can in turn be recorded by corresponding sensors 3. As in Fig. As shown schematically in Figure 2, the two sound waves 4a, 4b are identical in frequency and amplitude, but 180 degrees out of phase. The sound waves 4a, 4b are schematically represented as a temporal progression of the sound pressure.

[0022] The phase shift results from the fact that due to the axial distance d in the direction of the longitudinal axis x between the first web 11a and the second web 11b, the first sound wave 4a is generated before the second sound wave 4b, since the air flow 2 first hits the first web 11a and then the second web 11b.

[0023] Due to the phase shift, unlike in Fig. 1, a maximum of the sound pressure of one sound wave 4a is reduced to a minimum of the other sound wave 4b. This creates a “noise-cancelling effect” so that the sound pressure of a resulting sound wave 5 is significantly lower than that of the individual sound waves 4a, 4b taken on their own. Put simply, one could say that the first and second sound waves 4a, 4b cancel each other out. In this way, the noise generated by the ducted propeller can be significantly reduced. The distance d between the first web 11a and the second web 11b is preferably designed such that the phase shift between the first sound wave 4a and the second sound wave 4b is as close as possible to 180 degrees when the ducted propeller 1 is in continuous operation. Such continuous operation can occur, for example, in an aircraft at the intended cruising speed.

[0024] The Fig. 3a and Fig. 3b show a further embodiment of a ducted propeller 1 according to the invention. Here, only the differences regarding the embodiments of the Fig. 2 and Fig. 3a and 3b respectively.

[0025] In contrast to the embodiment according to Fig. 2 shows the embodiment according to Fig. 3a and Fig. 3b has two first webs 11a and two first webs 11b. The first webs 11a and second webs 11b are arranged evenly distributed in the circumferential direction around the longitudinal axis x and the central element 12 and thus enclose the same angle between them, i.e. from one web 11a, 11b to the next. The two first webs 11a and the two second webs 11b are arranged opposite one another with respect to the longitudinal axis x and the central element 12. In other words, this means that they enclose an angle of 180 degrees between them. The first webs 11a are, as already shown in Fig. 2, they are spaced apart from each other by a distance d along the longitudinal axis. The symmetrical arrangement ensures a uniform generation of the sound waves 4a, 4b and, at the same time, a uniform load distribution across the four webs 11a, 11b.

[0026] Preferably, the second webs 11b are designed to be displaceable in the direction of the longitudinal axis x, so that the distance d between the first webs 11a and the second webs 11b is adjustable. This can be implemented, for example, via linear guides in the housing 13 and the central part 12, with a linear drive in the housing 13 or central part 12, for example, driving the axial displacement. In this way, the phase shift between the resulting sound waves 4a, 4b can be adapted to the speed of the rotor 20. If the speed increases, the frequency of the sound waves 4a, 4b becomes greater, whereby the distance between the first webs 11a and the second webs 11b must be reduced so that the phase shift of 180 degrees between the sound waves 4a, 4b and thus the optimal possible noise reduction can be achieved. An embodiment with displaceable second orfirst webs 11b, 11a is of course also conceivable with other designs of the webs 11a, 11b and not limited to the ones in . Fig. 3a, Fig. 3b shown configuration.

[0027] Embodiments of the invention are also conceivable in which a different number of first webs 11a and second webs 11b are provided. In such an embodiment, the webs are designed such that the superposition of the sound waves 4a caused by the first webs 11a and the superposition of the sound waves 4b caused by the second webs 11b are identical, so that an axial spacing of the first and second webs 11a, 11b again leads to a phase shift of the superimposed first sound waves 4a and the superimposed second sound waves 4b. In this way, a compensation of the superimposed sound waves 4a, 4b can be achieved. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 692 24 853 T2

[0005] US 2004 234 372 A1

[0005] US 2012 328 432 A1

[0005] DE 100 53 361 C1

[0005]

Claims

[1] Having a ducted propeller (1), a stator (10) comprising a central element (12) extending along a longitudinal axis (x), and a housing (13) arranged around the central element (12), wherein the central element (12) is connected to the housing (13) via at least one first web (11a) and at least one second web (11b) arranged radially around the central element (12), a rotor (20) arranged on the central element (12) of the stator (10) with a plurality of rotor blades (21), designed to rotate about the longitudinal axis (x), wherein the rotor (20) is arranged in a flow direction of the ducted propeller (1) upstream of the at least one first web (11a) and at least one second web (11b), wherein the at least one first web (11a) of the stator (10) is arranged axially along the longitudinal axis (x) offset by a defined distance (d) from the at least one second web (11b), and the distance (d) is selected such that a first sound wave (4a) generated at the at least one first web (11a) due to the air flow is 180° out of phase with a second sound wave (4b) identical to the first sound wave (4a) generated at the at least one second web (11b) due to the air flow. [2] Ducted propeller according to the preceding claim, wherein the defined distance (d) between the at least one first web (11a) and the at least one second web (11b) is in a range between 0.05m and 0.28m. [3] Ducted propeller (1) according to one of the preceding claims, wherein the stator (10) has an even number of webs (11a, 11b) and half of the webs (11a, 11b) are first webs (11a) and half are second webs (11b). [4] Ducted propeller (1) according to the preceding claim, wherein the first webs (11a) and the second webs (11b) are arranged opposite one another with respect to the central element (12). [5] Ducted propeller (1) according to one of the preceding claims, wherein the stator has two first webs (11a) and two second webs (11b), and the first webs (11a) are arranged rotated by 90 degrees about the longitudinal axis (x) relative to the second webs (11b). [6] Ducted propeller (1) according to one of the preceding claims, wherein the first webs (11a) and / or the second webs (11b) are inclined in the flow direction of the ducted propeller (1). [7] Ducted propeller (1) according to one of the preceding claims, wherein the housing (13) is cylindrical. [8] Ducted propeller (1) according to one of the preceding claims, wherein the position of the at least one first web (11a) and / or the at least one second web (11b) is variable in the direction of the longitudinal axis (x), so that the distance (d) between the at least one first web (11a) and the at least one second web (11b) is adjustable. [9] Aircraft comprising a ducted propeller (1) according to one of the preceding claims.

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