Dulling propeller for an aircraft and aircraft

Abstract

A ducted propeller of an aircraft comprising a housing (38) which defines a cylindrical air duct (33) in the circumferential direction by means of an inner circumferential surface, and a propeller (34) which is arranged in the air duct (33), wherein the propeller (34) is rotatably mounted and can be driven by a drive unit (39), wherein an air outlet-side end face (43) of the housing (38) comprises a toothing (44) with a plurality of teeth (441), wherein the teeth (441) have a different tooth geometry.

Description

[0001] The invention relates to a ducted propeller for an aircraft and an aircraft.

[0002] Such ducted propellers are generally known from the state of the art and are used, for example, in so-called VTOLs (Vertical Take-Off and Landing). In aerospace engineering, the term VTOL refers to all types of aircraft or drones that can take off and land essentially vertically and without a runway. The ducted propellers can be arranged on the wings, in the tail area, or in the front area and perform different functions during horizontal and vertical flight. In addition, the ducted propellers can be fixed or adjustable about a rotation axis. Such a ducted propeller is disclosed, for example, in DE 10 2019 118 024 A1 or DE 10 2018 116 166 A1.

[0003] The disadvantage of such ducted propellers is that the air flowing out of the ducted propeller causes unwanted noise during flight. The noise is caused by the mixing of the air flowing out of the ducted propeller at high speed with the ambient air. This, combined with the sharp trailing edge of the ducted propeller, causes air turbulence, or turbulent flow, at the outlet of the ducted propeller, which leads to the unwanted noise.

[0004] US 2015 / 0 361 823 A1 and US 9 732 700 B2 disclose a ducted propeller for an aircraft. The ducted propeller comprises a housing whose inner circumferential surface defines a cylindrical air duct in the circumferential direction, and a propeller arranged in the air duct. The propeller is rotatably mounted and can be driven by a drive unit. An air outlet-side end face of the housing has a plurality of teeth with different tooth geometries.

[0005] It is the object of the invention to provide a ducted propeller in which the noise development at the air outlet is reduced in a simple and cost-effective manner.

[0006] The invention is solved by the features of claim 1.

[0007] The ducted propeller comprises a housing with an annular cross-section and an inner peripheral surface and an outer peripheral surface. The outer peripheral surface forms the outside of the ducted propeller and is either completely enclosed by another component of the aircraft, such as a wing, or, in the case of a freestanding ducted propeller, is enclosed by the environment.

[0008] The inner circumferential surface defines a cylindrical air duct which extends from an inlet-side end face of the housing or ducted propeller to an outlet-side end face of the housing or ducted propeller. The air duct is divided axially, i.e. in the longitudinal direction of the housing or along the axis of symmetry of the housing, into a plurality of sections which may have different lengths depending on the design. In particular, the air duct is divided into an air inlet section, a propeller section axially adjoining the air inlet section, and an air outlet section axially adjoining the propeller section. The air inlet section serves to ensure that the air flows into the air duct with as little loss as possible. Arranged in the propeller section is a propeller which is rotatably mounted, in particular rotatably mounted on the housing, and can be driven by a drive unit.The drive unit is preferably an electric drive unit, i.e., an electric motor. Typically, the electric motor is rigidly connected to the housing with the stator, and the propeller is attached to the rotor, which rotates during operation. The air outlet section serves to direct the air flowing from the propeller to the air outlet.

[0009] According to the invention, an end face of the housing on the air outlet side, i.e. a trailing edge of the housing, has a toothing with a plurality of teeth distributed over the circumference, wherein the teeth comprise a differing tooth geometry. The toothing is formed axially, i.e. in the longitudinal direction of the ducted propeller or in the direction of the propeller's axis of rotation. The toothing comprises a plurality of projections and valleys distributed in the circumferential direction and extending in the axial direction, which are different from one another, i.e. in height, width and radius. The toothing can comprise a toothed, sawtooth-shaped, wavy or other shape.

[0010] Such interlocking enables the airflow exiting the ducted propeller at a relatively high speed to be mixed more smoothly with the ambient air, which slows down the airflow exiting the ducted propeller or has a comparatively lower flow velocity, thereby reducing the noise generated at the ducted propeller outlet. In particular, the broadband noise at the ducted propeller outlet can be reduced. The mixing between the two airflows, i.e. the airflow exiting the air duct and the ambient air, does not occur abruptly, but at different, circumferentially spaced locations with a temporal and spatial offset. This leads to a more uniform transfer or mixing between the two airflows and thus reduces the noise caused by the airflows.

[0011] The air duct is radially widened at the air outlet section compared to the propeller section. The propeller section has a first diameter, with a second diameter of the air outlet section increasing continuously from the first diameter towards the end face on the air outlet side. By widening the air outlet section, noise development can be further reduced by slowing down the air flow before it exits into the atmosphere and thus shortly before it mixes with the ambient air. By slowing down the flow velocity of the air flow exiting the air duct, the speed difference between the air flow exiting the air duct and the ambient air or the air flow present in the ambient air can be reduced, thereby improving the mixing of the air flows. The air outlet section preferably forms an angle α of 0.5°-8° to the longitudinal axis of the housing.

[0012] The toothing preferably comprises a first toothing section extending over 180° and a second toothing section extending over 180°, wherein the toothing sections are identical. Preferably, the two toothing sections are mirrored relative to one another in a plane spanned by a vertical axis and a longitudinal axis. The dimensions of the teeth are in particular selected such that the distance between two adjacent teeth is (1+0.5x)a, the radius of the tooth tips is 10-40 mm, and the height of the teeth is 30-100 mm. A predetermined initial value a applies to the distance between the teeth, where x = 0 for the distance between the first and second tooth and x = 1, 2, 3, 4, ... for each additional tooth.For example, distance a applies to the distance between the first and second teeth, 1.5a applies to the distance between the second and third teeth, and 2a applies to the distance between the third and fourth teeth. This design enables the noise reduction effect of the gearing to be realized in a particularly strong manner.

[0013] Preferably, the wall thickness of the housing decreases in the region of the air outlet section toward the outlet end face. In other words, the widening of the air outlet section is achieved by reducing the wall thickness of the housing, wherein the outer peripheral surface of the housing, particularly in a horizontal flight phase, forms a continuous air guide surface for the air flowing around the ducted propeller. This prevents unwanted turbulence and turbulence due to the widening at the inner peripheral surface. The object is further achieved by an aircraft, particularly a VTOL, having at least one ducted propeller according to one of claims 1 to 8. The advantages are described in the preceding steps.

[0014] An embodiment of the invention is explained in more detail with reference to the drawings. Fig. 1 shows schematically a plan view of an aircraft, Fig. 2 shows schematically a ducted propeller of the aircraft from Fig. 1 in a cross-section, Fig. 3 shows schematically a section of the ducted propeller from Fig. 2 in a side view, and Fig. 4 shows a representation of a developed tooth geometry of a toothing on an air outlet-side end face of the ducted propeller from Fig. 2 and Fig. 3.

[0015] Fig. Figure 1 shows an aircraft 10, in particular a VTOL. In addition to horizontal flight, such an aircraft 10 designed as a VTOL can take off and land essentially vertically and without a runway. This requires that the aircraft 10 comprises appropriate components.

[0016] The aircraft 10 comprises a fuselage 12 that extends the entire length of the aircraft 10 and forms the supporting element of the aircraft 10. The fuselage 12 includes a passenger cabin 14 in the front area, in which passengers and a pilot can fly to control the aircraft 10. A wing 16, 18 is arranged on each of two opposite sides of the fuselage 12, which are particularly necessary for a horizontal flight phase.

[0017] The aircraft 10 also comprises a plurality of ducted propellers 22, 24, 26, 28. Two ducted propellers 22, 24 are arranged on the wings 16, 18, with one ducted propeller 22, 24 being provided on each wing 16, 18. The ducted propellers 22, 24 arranged on the wings 16, 18 are rigidly mounted on the wings 16, 18 and oriented in the vertical direction. The two ducted propellers 22, 24 are thus used in particular for a vertical flight phase, i.e., for landing and takeoff. Two further ducted propellers 26, 28 are arranged in the rear region of the aircraft 10 and attached to the fuselage 12. The ducted propellers 26, 28 are each pivotably mounted on the fuselage 12 about a rotation axis D1, D2 and can be actively adjusted between a vertical and a horizontal position by an adjustment device not shown in the figures.The adjustment of the ducted propellers 26, 28 means that they are used in the vertical position for propulsion in the vertical flight phase and in the horizontal position for propulsion in the horizontal flight phase.

[0018] Fig. 2 shows a cross-section of the ducted propellers 26, 28. The ducted propellers 22, 24 can be designed in the same or different ways. The ducted propeller 26, 28 comprises a housing 38, wherein the housing 38 borders the environment with its outer peripheral surface and defines an air duct 33 with its inner peripheral surface. The air duct 33 comprises an air inlet 40 and an air outlet 42. In the longitudinal direction, the air duct 33 is divided into an air inlet section EA extending from the air inlet, a propeller section PA axially adjoining the air inlet section EA, and an air outlet section AA axially adjoining the propeller section PA.

[0019] In each case, a propeller device 30, 32 is arranged in the air duct 33 of the ducted propeller 26, 28, i.e., in the propeller section PA of the air duct 33. The propeller device 30, 32 comprises a propeller 34 driven by an electric drive unit 39 and a plurality of rigidly arranged air guiding elements 36. A stator of the electric drive unit 39, not shown in the figure, is attached to the air guiding elements 36. A rotor of the electric drive unit 39, which is also not shown in the figures, is connected to the propeller 34. By actuating the electric drive unit 39, the propeller 34 rotates and causes an air flow from the environment into the air duct 33. The electric drive 39 is supplied with electrical energy as needed by a battery arranged on the fuselage 12, wherein the battery is not shown in the figures.The air flow flows out of the air duct 33 again via the air outlet 42 at a relatively high flow velocity.

[0020] The disturbing aspect of the air flowing out of the air duct 33 is that it causes undesirable noise during flight operation. The reason for this is the mixing of the air flowing out of the air duct 33 at a high flow velocity with the essentially slower ambient air or with an ambient air flow with a reduced flow velocity. The mixing of the air flows with different flow velocities causes turbulence on an outlet-side end face 43 of the housing 38, which leads to noise during flight operation.

[0021] In order to reduce noise, the end face 43 of the housing 38 on the air outlet side has a toothing 44 with a plurality of teeth 441 distributed in the circumferential direction, wherein the teeth 441 comprise a tooth geometry that differs from one another. Such a toothing 44 is shown in Fig. 3 shown. Fig.4 shows the tooth geometry of the teeth 441 in a developed view. The toothing 44 comprises two toothing sections VA1, VA2, each extending over 180° and merging directly and continuously into one another. The two toothing sections VA1, VA2 are identically formed and mirrored relative to one another in a plane E spanned by a vertical axis and a longitudinal axis. The teeth 441 of the two toothing sections VA1, VA2 comprise a geometry that differs from one another such that the distance A between the teeth 441 has the shape of (1+0.5x)a, where a is a predetermined value and x = 0, 1, 2, 3, 4, 5, ... increases with each tooth 441, the radius R of the teeth 441 varying between 10-40 mm and the height H of the teeth 441 varying between 30-100 mm.

[0022] By means of such a toothing 44 formed on the end face 43 on the air outlet side, the air flow flowing out of the air duct 33 at a relatively high speed can be mixed more evenly with the ambient air, which has a lower flow velocity than the air flow flowing out of the ducted propeller, thereby reducing noise generation and, in particular, so-called broadband noise at the outlet of the ducted propeller. As a result, the mixing between the two air flows, i.e., the air flow exiting the air duct and the ambient air, does not occur abruptly, but at different locations spaced apart from one another in the circumferential direction, with at least a slight temporal and spatial offset.

[0023] In addition, the air duct 33 is radially widened at the air outlet section AA compared to the propeller section PA, the widening being achieved by reducing the wall thickness of the housing 33. The propeller section PA has a first diameter D1, and the air outlet section AA has a second diameter D2 at the outlet-side end face 43, the second diameter D2 being larger than the first diameter D1, and the diameter of the air outlet section AA increasing continuously from the first diameter D1 toward the air outlet-side end face 43. The difference between the diameters D1, D2 can be selected such that the inner circumferential surface of the air duct 33 at the air outlet section encloses an angle α of 0.5°-8° to the longitudinal axis of the housing 38.

[0024] By widening the air outlet section AA, the noise generation can be further reduced by slowing down the air flow before it exits into the outside atmosphere and thus shortly before it mixes with the ambient air, thereby reducing the speed difference between the air flow exiting the air duct 33 and the ambient air.

[0025] In this way, a ducted propeller 26, 28 is provided in a simple and cost-effective manner which can be operated with reduced noise.

Claims

[1] Ducted propeller of an aircraft, comprising a housing (38) defining a cylindrical air channel (33) in the circumferential direction by an inner circumferential surface, and a propeller (34) arranged in the air duct (33), wherein the propeller (34) is rotatably mounted and can be driven by a drive unit (39), characterized by , that an air outlet-side end face (43) of the housing (38) comprises a toothing (44) with a plurality of teeth (441), wherein the teeth (441) have a different tooth geometry from one another, wherein the air duct (33) comprises a propeller section (PA) and an air outlet section (AA) axially adjoining the propeller section (PA), wherein the air duct (33) is radially widened at the air outlet section (AA) with respect to the propeller section (PA). [2] Ducted propeller according to claim 1, wherein the toothing (44) comprises a first toothing section (VA1) extending over 180° and a second toothing section (VA2) extending over 180°, wherein the toothing sections (VA1, VA2) are of identical design. [3] Ducted propeller according to claim 2, wherein the two toothed sections (VA1, VA2) are mirrored relative to one another in a plane (E) spanned by a vertical axis and a longitudinal axis of the housing (38). [4] Ducted propeller according to one of the preceding claims, wherein the distance (A) between two adjacent teeth (441) is in each case (1+0.5x)a. [5] Ducted propeller according to one of the preceding claims, wherein the radius (R) of the tips of the teeth (441) is 10-40 mm and the height (H) of the teeth is 30-100 mm. [6] Ducted propeller according to one of the preceding claims, wherein the propeller section (PA) comprises a first diameter (D1), wherein a second diameter (D2) of the air outlet section (AA) increases continuously from the first diameter (D1) towards the air outlet end face (43). [7] Ducted propeller according to one of the preceding claims, wherein the air outlet section (AA) encloses an angle α of 0.5°-8° to the longitudinal axis of the housing (38). [8] Ducted propeller according to one of the preceding claims, wherein the wall thickness of the housing (38) decreases with the widening in the region of the air outlet section (AA) towards the outlet-side end face (43). [9] Aircraft having at least one ducted propeller (26, 28) according to one of claims 1 to 8.

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