Rotor system for an aircraft

Abstract

The present invention relates to a rotor system (10) for an aircraft (1), the rotor system comprising: a drivable rotor (20) having a plurality of rotor blades (21) and a rotor shroud (30), the rotor blades being arranged substantially radially about a rotation axis (R) of the rotor (20), planes perpendicular to the rotation axis (R) and passing radially through the rotor blades (21) forming a rotor plane (RA), the rotor shroud surrounding the rotor (20) about the rotation axis (R) and defining the air of the rotor (20) extending axially along the rotation axis (R). The channel (40) wherein the rotor shroud (30) is configured as a hollow structure (31) surrounding the axis of rotation (R), the hollow structure having at least a section of a gas-permeable region (32a) on its circumferential surface (32) facing the rotor (20) in the radial direction, the rotor plane (RA) intersecting the gas-permeable region (32a), and the hollow structure (31) being configured such that at least one frequency of sound waves passing through the gas-permeable region (32a) into the hollow structure (31) are at least partially absorbed by the hollow structure (31).

Description

Technical Field

[0001] This invention relates to a rotor system for aircraft. Background Technology

[0002] The operation of the rotor system generates acoustic emissions, which can be considered interference in terms of both volume and frequency. Therefore, for applications involving rotor systems of aircraft operating near residential areas, measures should be taken to reduce the volume emitted into the environment, or at least reduce the volume at a given frequency.

[0003] To reduce sound emissions from a rotor system, it is known, for example, to provide aeroacoustic linings and aerodynamic linings. Aeroacoustic linings reduce the sound typically generated by the rotor, while aerodynamic linings are designed to reduce sound emissions caused by vortices at the rotor blade tips.

[0004] To address this, EP2913269A1 proposes for the tail rotor of a helicopter that an aerodynamic liner in the form of a separate channel is provided in a region of the rotor plane. An aeroacoustic liner, constructed of cross-linked or interlaced hollow structures, is also provided on the air outlet side of the rotor. However, this prior art has several drawbacks. For example, placing the aeroacoustic liner next to the aerodynamic liner requires corresponding installation space in the axial direction relative to the rotor's axis of rotation. Furthermore, the effect of the aeroacoustic liner is limited to the region of the air outlet side, thus sound emission on the air intake side of the rotor is not reduced or only limitedly reduced. The aeroacoustic liner, in particular, cannot be implemented continuously because the rotor's stator or struts are located in the region of the aeroacoustic liner. Finally, the weight of the tail rotor system is increased, however, due to the additional introduction of separate channels for constructing the cross-linked or interlaced single hollow structures for both the aerodynamic and aeroacoustic liners. Summary of the Invention

[0005] In view of the disadvantages associated with the prior art, the object of the present invention is to provide a rotor system for an aircraft, which is constructed in a compact manner with an aerodynamic liner and an aeroacoustic liner to reduce sound emissions.

[0006] The objective of the invention is achieved by a rotor system for an aircraft according to the invention.

[0007] Here, the present invention can generally be applied to the rotor system of aircraft. In particular, the present invention can provide a tail rotor for helicopters.

[0008] According to the present invention, a rotor system for an aircraft includes: a drivable rotor having a plurality of rotor blades arranged substantially radially about an axis of rotation of the rotor, and a plane passing through the rotor blades in a radial direction perpendicular to the axis of rotation forming a rotor plane; and a rotor shroud surrounding the rotor about the axis of rotation and defining an air passage of the rotor extending in an axial direction along the axis of rotation, wherein the rotor shroud is configured as a hollow structure about the axis of rotation, the hollow structure having at least a section of a gas-permeable region on its circumferential surface facing the rotor in a radial direction, the rotor plane intersecting the gas-permeable region, and the hollow structure being configured such that sound waves of at least one frequency entering the hollow structure through the gas-permeable region are at least partially absorbed by the hollow structure.

[0009] The term "substantially radial" regarding the arrangement of rotor blades refers to the basic orientation of the rotor blades. However, the blades are not necessarily required to be strictly constructed radially. Rotor blades may, for example, have an angle of attack relative to their geometric radius, and the basic orientation is always radial, in the sense that the rotor blades are arranged radially about the axis of rotation. Furthermore, rotor blades do not need to be equidistant, but can have different spacings relative to each other, so as to, for example, be able to split acoustic energy into multiple frequencies.

[0010] The rotor shroud is constructed as an aerodynamic liner and an aeroacoustic liner via a hollow structure that interacts with at least sectionally formed gas-permeable regions. In other words, the aerodynamic liner and aeroacoustic liner are formed by the main structure of the rotor shroud without necessarily requiring other separate shroud elements. The term "main structure" is used to clarify that the rotor shroud constructed as a hollow structure does not involve additional structural elements not belonging to the rotor shroud itself, but rather refers to the actual arrangement of the elements of the shell for the shroud. Thus, the hollow structure is formed by corresponding inner surfaces opposite to the outer surfaces of the shroud. In other words, the hollow structure is therefore formed by the shroud elements constituting the shell of the rotor shroud. Sound waves entering through the gas-permeable regions are directed into a volume that extends radially about the axis of rotation from the gas-permeable regions to the opposite inner surfaces of the rotor shroud or main structure. Due to the rotor shroud surrounding the axis of rotation, a similarly surrounding hollow structure is created. This hollow structure is continuous, especially without the addition of other reinforcing elements and / or cavity elements, which will be described later. Therefore, the hollow structure formed by the rotor shroud itself creates a globally effective hollow structure. In other words, the cavity formed by the hollow structure extends continuously in the circumferential direction. Although, for example, the reinforcing elements and / or cavity elements described above and explained below can be adapted to a locally effective hollow structure, this relates to extensions of the invention. Even taking into account other structural elements introduced besides the rotor shroud, the absorption characteristics of sound waves entering through the gas-permeable region are decisively determined by the rotor shroud itself.

[0011] Preferably, the gas-permeable region is not constructed as segmental along the circumferential direction, but as a whole, so as to function circumferentially over the entire periphery in a manner that cooperates with the hollow structure. This is generated solely by the rotation of the rotor blades, which correspond to the initial movement of the rotor blades without localized acoustic emissions and / or vortex maxima at the blade tips. However, such maxima can thus occur locally in interaction with other structural components of the rotor system and / or in relation to the distribution and / or mounting of the rotor blades, thus providing one or more gas-permeable regions segmentally may be sufficient.

[0012] Within the operational mode of the rotor shroud's aerodynamic lining, rotor blade tip vortices, during rotor operation, impact gas-permeable regions in the rotor plane located on the circumferential surface facing the rotor blades. These blade tip vortices can penetrate these regions into the hollow structure, where they are at least partially absorbed, and in particular dissipated. Blade tip vortices that do not enter the hollow structure are at least dispersed. Besides acoustic effects, this dissipation, for example due to at least a partial reduction in the rotor blade tip angle, can also influence aerodynamic drag and thus potentially increase thrust generation effectiveness.

[0013] However, sound waves also penetrate the gas-permeable region into the hollow structure, which at least partially absorbs sound waves of at least one frequency and thus acts as a sound lining. Essentially, in this context, the terms absorption and damping of sound waves can be used synonymously, with dissipation, for example, constituting a specific form of absorption or damping due to energy conversion. The frequency of occurrence is constant at the rotor's predetermined rotational speed; however, the amplitude of the corresponding frequency can vary depending on the current setup of the rotor system, for example, according to the angle of attack of the rotor blades. Therefore, the hollow structure can, for example, be designed to at least partially absorb one or more frequencies considered particularly disturbing, even if said frequencies may not cause or always cause a maximum sound level. The at least partial absorption characteristic of the hollow structure can be achieved not only geometrically but also alternatively or supplementally through the selection of corresponding materials.

[0014] By positioning the combined aerodynamic and aeroacoustic linings in the rotor plane, it is possible to implement them without interruption over the entire periphery of the rotor shroud.

[0015] The aforementioned rotor system thus weakens the aerodynamic effects of the rotor blade tip vortices in the gas-permeable region through the combination of the gas-permeable region and the hollow structure, and at least partially absorbs and thus dampens the incoming sound waves, thereby enhancing its thrust-generating effect. Because the outer contour of the rotor shroud does not need to be altered, the aerodynamic function of the rotor shroud for thrust generation is also maintained. However, depending on the frequency to be damped, the rotor shroud can be adapted while taking aerodynamic effects into account. Alternatively or additionally, measures involving the volume within the hollow structure can also be taken, as will be adopted later regarding additional components and / or material structures.

[0016] In one design, the hollow structure is spaced apart from the circumferential surface opposite the gas-permeable region on the side away from the rotor blades, such that the gas-permeable region and the opposite circumferential surface are at least sectionally configured as λ / 4 resonators for the at least one frequency.

[0017] The circumferential surface of the hollow structure opposite the gas-permeable region on the side facing away from the rotor blades can also be called the outer operating inner surface. Conversely, the side of the circumferential surface with the gas-permeable region facing the inner surface of the outer operating inner surface is the inner operating inner surface. By separating the outer operating inner surface and the inner operating inner surface according to the λ / 4 resonator, standing waves or multiple quarter-wavelengths (harmonics) of corresponding wavelengths, frequencies, or mode combinations can be constructed in the hollow structure. Combined with the gas-permeable region that constitutes acoustic resistance in this case, the acoustic energy of the corresponding frequency is at least partially converted into heat energy, which constitutes absorption. The spacing can be constant along the circumferential direction, or it can be varied at least segmentally along the circumferential direction to locally tune to different frequencies. This tuning can alternatively or additionally be set perpendicular to the circumferential direction, i.e., relative to the axis of rotation along the axial direction. This proves particularly advantageous in cases where different maximum values ​​of a given frequency along the axial direction can occur, for example, this can occur when the angle of attack of the rotor blades is different, which will be discussed again later. The spacing between the outer and inner circumferential surfaces can be constructed by correspondingly setting the rotor shield material or by correspondingly contouring the material. Material contouring can be, for example, by varying the cross-section of the material so that the outer and inner rotating surfaces can have locally different spacings, even though the materials are spaced apart parallel to each other.

[0018] Alternatively or additionally, the hollow structure is at least sectionally configured as a Helmholtz resonator for the at least one frequency.

[0019] Helmholtz resonators are particularly suitable for absorbing or damping lower frequencies. Because intermediate and higher frequencies are damped only to a limited extent, hollow structures can be constructed using other resonator principles, such as at least sectionally constructing λ / 4 resonators.

[0020] In addition to geometric design schemes based on λ / 4 resonators, Helmholtz resonators, or combinations thereof, or other resonator principles, acoustic damping characteristics can be enhanced through material selection and / or surface structure. Structural features of Helmholtz resonators can, for example, be used to dampen lower frequencies, while structural features of λ / 4 resonators can be used to dampen medium and / or higher frequencies.

[0021] In one extended embodiment, the surrounding hollow structure is configured to be fluid-permeable, at least in sections circumferentially parallel to gravity orientation.

[0022] Liquids, such as precipitation or cleaning water, can enter the hollow structure through gas-permeable areas or other openings in the rotor casing. Depending on the location of each opening, these liquids can also be discharged. During cleaning, water can enter, for example, through a section of the hollow structure with a gas-permeable area, oriented spatially such that water is discharged in the direction of gravity. However, not all sections of the surrounding hollow structure offer this discharge possibility. In particular, sections oriented circumferentially parallel to gravity and therefore also via gas-permeable areas, and which do not have outlets in this section, should be constructed to be fluid-permeable. Here, fluid permeability is not for outward discharge, but rather relates to fluid guidance within the hollow structure, so that the entering liquid can be guided at least to the permitted discharge section within the hollow structure. Because the rotor system according to the invention can be directly constructed via the main structure, internal fluid guidance via the hollow structure can be achieved in a simple manner.

[0023] However, at least in sections, the fluid-permeable construction of a hollow structure also allows for the extension of the usable resonant cavity in the circumferential direction. For this purpose, it can be assumed that fluid permeability in this case also results in gas permeability. Even if a resonant cavity is not formed in the sense of constructing a standing wave, at least individual frequencies can be damped, for example, by dissipation.

[0024] Preferably, the hollow structure has at least one discharge port.

[0025] Liquid entering the hollow structure can be selectively discharged via a vent. Therefore, if the vent can be selectively opened and closed, the discharge location can be strategically chosen and / or the discharge time can be predetermined. The vent can be formed via a gas-permeable area. However, this is insufficient in many cases because, for example, the gas-permeable area of ​​a helicopter tail rotor does not constitute the lowest point of the hollow structure when stationary. Therefore, in such cases, the gas-permeable area may only function as an overflow outlet, but does not independently discharge fluid from the hollow structure located below the gas-permeable area. Thus, a separate vent can be advantageous.

[0026] The rotor blades have, in particular, an angle of attack that is variably adjustable about an axis radially about the axis of rotation, and the gas-permeable region extends axially about the axis of rotation at least over the region covering the rotor blade position that can be achieved via the angle of attack.

[0027] The angle of attack of the rotor blades is changed according to the flight maneuver to be performed. Therefore, the location of the region generating vortices at the rotor blade tips also changes. To include all locations of these angle-of-attack-related vortices, the gas-permeable region extends at least segmentally, particularly along the circumferential direction across the entire circumferential plane, and along the axial direction at least over the region that can cover all rotor blade positions according to the rotor blade angle of attack. Otherwise, i.e., in the axial extension of the gas-permeable region (which does not cover all adjustable rotor blade positions), the aerodynamic effect of the gas-permeable region is nonexistent or at least very limited for all rotor blade positions or rotor blade angles of attack.

[0028] Because the propagation of the vortex at the rotor blade tip along the radial direction relative to the rotor's axis of rotation is not limited to the area defining the rotor blade tip, and because the vortex can propagate not purely radially but also scatteringly along the axial direction, the gas-permeable region can be constructed along the axial direction, particularly covering an area larger than the rotor blade position. Preferably, the gas-permeable region extends axially outward from the rotor plane, at least on one side, particularly on both sides, covering an area corresponding to the rotor blade position based on the rotor blade's angle of attack.

[0029] In one design, the porosity of the gas-permeable region is between 5% and 90%.

[0030] The gas-permeable region is defined in principle as the region that has primary gas permeability compared to other regions of the rotor shroud. The term "primary" here does not necessarily imply more than 50% gas permeability, but rather refers to the material properties identified as gas-permeable. This region is defined here by the outermost gas-permeable openings (e.g., pores) before the rotor shroud transitions into the gas-impermeable material region.

[0031] Therefore, if the gas-permeable region is now composed of pores, the cavity volume—that is, the volume of all the pores in that region—accounts for between 5% and 90% of the total volume of that region. When the cavity volume share is low, the rotor blade tip angle is primarily reflected and no longer introduced into the hollow structure. Therefore, the aerodynamic liner no longer functions effectively. Similarly, the acoustic bandwidth of the λ / 4 resonator is affected, and simultaneously, for very low frequencies (which are no longer relevant to the audible range), the operating mode of the λ / 4 resonator liner shifts towards that of the Helmholtz resonator. When the cavity volume share exceeds 90%, the absorption or damping capability can be decisively reduced if the rotor blade tip eddies and / or sound waves entering through the pores can be expelled again without significant damping.

[0032] According to one extended embodiment, the porosity changes axially about the axis of rotation starting from the rotor plane. Specifically, the porosity increases outward from the rotor plane towards at least one side.

[0033] By altering the porosity along the axial direction, the acoustic impedance and thus the acoustic characteristics of the aerodynamic and aeroacoustic linings can be locally adapted. This is particularly advantageous in rotor blades with adjustable angles of attack, as the frequency amplitude shifts along the angle of attack. Preferably, this larger porosity, i.e., a larger cavity volume, is located in the outer region of the gas-permeable area, which is significant when the rotor blade has a large angle of attack. The altered porosity can here be expressed as porosity per unit area.

[0034] Alternatively or additionally, the porosity varies along the circumferential direction of the gas-permeable region.

[0035] The porosity that varies along the circumferential direction allows for impedance adaptation along the periphery and thus for acoustic characteristics. Therefore, even when the adjustable angle of attack of the rotor blades can be taken into account, the interaction between sound emission and the different structural elements along the periphery can be considered.

[0036] By combining variations in porosity along the axial and circumferential directions, acoustic properties can be optimized in a way that is determined by the structure and operation.

[0037] In one design, the gas-permeable area is composed of microperforations, perforated plates, and / or wire mesh.

[0038] Microperforations in the rotor shroud contour or sections of the rotor shroud contour can introduce gas permeability for gas-permeable areas without structural interruption. Furthermore, the distribution of microperforations can be precisely implemented as needed. Individual introduction of perforated plates and / or wire mesh allows for flexible adaptation of acoustic characteristics by changing the appropriate inserts. Moreover, in this case, different material properties can be utilized regardless of the material of the actual rotor shroud.

[0039] According to one extension, the hollow structure has reinforcing elements and / or hollow structural elements that have a sound-absorbing effect or are conducive to sound absorption in their position and / or design.

[0040] Therefore, targeted reinforcing elements for stability, or other hollow structural elements such as those for pipeline guidance, can be used to improve the sound attenuation and / or sound damping performance of the rotor system. This eliminates the need for additional components and structures solely for sound absorption.

[0041] The positioning can be performed circumferentially based on the frequency to be at least partially absorbed, for example, by the inherent frequency of the gas volume enclosed within the entire structure or acoustically separated subspaces. Alternatively or additionally, the circumferential positioning can also be performed based on the local interaction between sound emission and the corresponding structural components. Through this positioning, the depth and / or volume of the hollow structure can thus be influenced via reinforcing elements and / or hollow structural elements to specifically increase at least partial absorption of at least one frequency. Correspondingly, this can also transform a hollow structure with global acoustic effects (such as one that can be constructed, for example, by means of a continuous circumferential structure without reinforcing elements and / or hollow structural elements) into a hollow structure with local acoustic effects.

[0042] In contrast, the design of reinforcing elements and / or hollow structural elements involves specific geometries such as profiles or material thickness, the materials to be used, and / or different surface properties, such as those that can be achieved through coatings or surface structuring.

[0043] In particular, the hollow structure effectively absorbs sound waves entering within a wide frequency range.

[0044] The design of a broadband liner is decisively influenced by the structure's role as an aeroacoustic liner, facilitated by the variable depth of the hollow structure, i.e., the radial spacing about the axis of rotation. Furthermore, the bandwidth can be increased at the cost of absolute absorption by appropriately selecting perforations in the gas-permeable areas.

[0045] In one design, the hollow structure at least partially absorbs incoming sound waves in the frequency range from 30 Hz to 1500 Hz.

[0046] Within this frequency range, frequencies also considered particularly disruptive occur. However, this range also includes frequencies with typically perceptible maximum amplitude. Correspondingly, the overall volume level can be reduced when appropriately selected.

[0047] According to one extended embodiment, the rotor system includes at least one support column disposed on the air intake side of the rotor system.

[0048] Stator struts, sometimes also called stator struts, are used for suspending the rotor hub. The rotor hub is typically located on the air output side of the rotor system, and a relatively wide air passage along the axial direction of the rotation axis, formed by the rotor shroud, compensates for the sound emissions associated with this arrangement. However, if at least one strut used to suspend the rotor hub is now located on the air intake side, sound emissions otherwise caused by the impact of air accelerated by the rotor onto the strut are reduced. In other words, other sound sources on the air output side are thus avoided, thereby reducing the axial width of the air passage. The air intake side is understood as the side that draws in air for most flight maneuvers. Similarly, the air output side is understood as the side that exhausts air for most flight maneuvers.

[0049] Preferably, the at least one support is eccentrically arranged about the axis of rotation.

[0050] Due to the temporally staggered interaction between the wake concave portion of the inflow velocity distribution caused by the shielding effect of the struts during normal operation and the leading edge of the rotating rotor blades, the eccentrically arranged structure assists in reducing sound emission, i.e., for torque compensation of the main rotor. Similarly, no simultaneous interaction occurs when the rotor blades are at a negative angle of attack due to the maneuvering of the flight device. However, in this case, it refers to the interaction between the vortices generated by the rotating rotor blades and the struts responsible for generating sound. Attached Figure Description

[0051] The features, objectives, and advantages of the invention are then described with reference to the accompanying drawings and embodiments.

[0052] In the attached image:

[0053] Figure 1 A schematic diagram of an aircraft having a rotor system according to an exemplary embodiment of the present invention is shown;

[0054] Figure 2 Showing according to Figure 1 A perspective view of the rotor system;

[0055] Figure 3 Showing according to Figure 1 and Figure 2 A partial perspective cross-sectional view of the rotor system in a section parallel to the axis of rotation;

[0056] Figure 4 Showing according to Figure 3 A schematic cross-sectional view of the rotor system, wherein the view is directed toward the cross section and shows the mounting area of ​​the rotor blades;

[0057] Figure 5 Showing according to Figure 1 and Figure 2 A partial perspective cross-sectional view of the rotor system in a section perpendicular to the axis of rotation. Detailed Implementation

[0058] Figure 1 An aircraft 1, here a helicopter, is shown with a rotor system 10, which in the illustrated embodiment serves as the tail rotor system of the helicopter. The rotor system 10 includes a rotor 20 and a rotor shroud 30. The rotor has rotor blades 21 arranged around a rotor hub 23, which is held by, preferably, a plurality of struts 22. The struts 22 are located on the air intake side 41 (…). Figure 2 ) on, so as to avoid air output side 42 ( Figure 2 Other sound sources on the rotor blades. Furthermore, the eccentric arrangement of the strut 22 about the axis of rotation R also produces a positive acoustic effect. The air intake side 41 or air output side 42 are the sides from which air is drawn in or expelled for most flight maneuvers, respectively. In other words, air can also be output from the air intake side 41 when the angle of attack of the rotor blades 21 is correspondingly negative; however, this is only assumed in a few cases during flight operation, making such a situation negligible in defining the air intake side 41. The same applies to the air output side in the reverse case.

[0059] according to Figure 2 The rotor shroud 30 surrounds the rotor 20 circumferentially about the axis of rotation R and defines an air passage 40 extending axially along the axis of rotation R. Air is transported from the air intake side 41 to the air output side 42, also known as the thrust side, by the rotation of the rotor blades 21 about the axis of rotation R. The airflow direction is... Figure 2 The arrow also indicates that this can be reversed depending on the installation of the rotor blades. (As shown from...) Figure 4 As can be seen further, in the rotor plane RA formed by the rotor blades 21 perpendicular to the axis of rotation R, the circumferential surface 32 of the rotor shroud 30 facing the rotor 20 has a gas-permeable region 32a, which intersects the rotor plane RA and extends axially to both sides of the rotor plane RA about the axis of rotation R.

[0060] to this end, Figure 3 Show in detail according to Figure 1 and Figure 2A partial perspective cross-sectional view of the rotor system 10 in a section parallel to the axis of rotation R. In this exemplary embodiment, the gas-permeable region 32a is constituted by a perforated plate with micro-perforations, which is inserted into and fixed in the rotor shroud 30. The porosity introduced by the micro-perforations is, for example, 50% and is constant about the axis of rotation R in both the circumferential and axial directions. However, the porosity may also vary about the axis of rotation R in both the circumferential and axial directions and / or be less than or greater than 50%. The selection of porosity or its distribution can arise from the interaction of corresponding optimization objectives in terms of aeroacoustic or aerodynamic effects with corresponding structural construction.

[0061] The gas-permeable region 32a covers the radial projection of the rotor blade tip of the rotor blade 21, such that the rotor blade tip vortices generated in the gap between the rotor blade tip and the gas-permeable region 32a can be introduced through the gas-permeable region 32a into the hollow structure 31 formed by the rotor shroud 30, where they are dissipated or otherwise damped, thereby achieving an aerodynamic effect. Here, the aerodynamic effect involves, on the one hand, the acoustic effect caused by eliminating or transferring the sound source associated with the rotor blade tip vortices into the hollow structure 31. On the other hand, the efficiency of the rotor system 10 is increased by the reduction of drag caused by the attenuation and / or transfer of the rotor blade tip vortices. Furthermore, the aeroacoustic function is implemented through the gas-permeable region 32a in a volumetric coupling with the hollow structure 31, wherein the sound waves coupled into the hollow structure 31 via the gas-permeable region 32a also achieve a purely acoustic effect by at least partially absorbing at least one frequency, which is generated, for example, by other components different from the rotor blade tip during rotor 20 operation. Therefore, in the illustrated embodiment, the inner surface of the circumferential surface 33 facing away from the rotor 20, i.e., the outer operating inner surface 33a, is spaced apart from the inner surface of the circumferential surface 32 facing away from the rotor 20, i.e., the inner operating inner surface 32b, so as to be configured as a λ / 4 resonator for at least one frequency.

[0062] Therefore, an aerodynamic and aeroacoustic lining is formed by positioning and defining the size of the gas-permeable region 32a in a manner that works in conjunction with the volume of the hollow structure 31.

[0063] Figure 4 Show again according to Figure 3 A schematic cross-sectional view of the rotor system 10, with the view directed toward the cross-section, to illustrate the adjustable mounting area of ​​the rotor blades 21 and the coverage of the rotor blade tips within this mounting area by a gas-permeable region 32a. For this purpose, in Figure 4The diagram shows the position where rotor blade 21 can be maximally mounted when rotating about an axis X radially about the rotation axis R. Starting from the rotor plane RA coinciding with the radial axis X, the gas-permeable region 32a extends axially to both sides about the rotation axis R, covering the maximum position of the rotor blade tip. In the exemplary embodiment shown, the gas-permeable region 32a is also expanded relative to the maximum position of the rotor blade tip so that dispersed rotor blade tip vortices can also be introduced into the hollow structure.

[0064] With the help of Figure 5 Showing according to Figure 1 and Figure 2 A partial perspective cross-sectional view of the rotor system 10 in a section perpendicular to the axis of rotation R. Here, the rotor shroud 30 is constructed as a hollow structure 31, wherein the spacing between the outer and inner circumferential surfaces differs along the circumferential direction. Therefore, locally differentiated λ / 4 resonators are constructed such that the locally differentiated frequencies can be at least partially absorbed, which overall reduces the volume and imparts a broadband acoustic effect to the liner. In particular, different spacings can be specified such that preferred damping corresponds to the tonal components of the rotor's rotational frequency and / or otherwise considered particularly disturbing frequencies.

[0065] Furthermore, the hollow structure 31 has different reinforcing elements 34 and hollow structural elements 35. The reinforcing element 34 here serves, for example, as a baffle and similarly affects the damping of sound waves introduced into or propagating in the hollow structure in terms of its size and positioning. In a similar manner, the additionally introduced hollow structural elements 35 can be constructed as chambers in the hollow structure 31 to, for example, constitute locally different resonator volumes and thereby affect the damping at frequency. However, here the damping capability is decisively determined by the main structure of the rotor shield 30.

[0066] according to Figure 5 The rotor shroud 30 also has a discharge port 36 through which liquid entering the hollow structure 31 can be discharged. The discharge port 36 is located in the region of the rotor shroud 30 below the direction of gravity, where liquid accumulates due to gravity. Therefore, the hollow structure 31 is preferably a partially fluid-permeable, i.e., constructed as a continuous, circumferential fluid channel. Even if the reinforcing element 34 and / or the hollow structural element 35 are disposed within the hollow structure 31, the reinforcing element and / or the hollow structural element should therefore be at least partially fluid-permeable or disposed in locations that allow liquid to drain in other ways. The latter can be achieved by... Figure 5The hollow structural element 35 shown is used as an example. If these hollow structural elements are not implemented to be fluid-permeable, they are at least located in positions where liquid in the upper chamber formed by the hollow structural element 35 can be led out via a gas-permeable region 32a (not shown here). Therefore, the gas-permeable region 32a will also be fluid-permeable.

[0067] This invention is not limited to the described embodiments. In particular, the defining characteristics of possible variations or extensions are also applicable in principle to the described or other embodiments, provided that this is not reasonably excluded. Even if, for example, the rotor hub 23 is held by two struts 22, only one strut may be provided. It is also possible to use more than two struts. However, the use of the rotor system 10 is not limited to the tail rotor system of helicopters, but can also be used for other aircraft, such as drones or air cockpits.

[0068] List of reference numerals

[0069] 1. Aircraft

[0070] 10 Rotor System

[0071] 20 rotors

[0072] 21 Rotor blades

[0073] 22 pillars

[0074] 23 Rotor hub

[0075] 30 Rotor shroud

[0076] 31 Hollow Structure

[0077] 32 circumferential surfaces (facing the rotor)

[0078] 32a Gas-permeable zone

[0079] 32b Inner circumferential surface

[0080] 33 Circumferential plane (away from rotor)

[0081] 33a Peripheral surface

[0082] 34 Reinforcing Components

[0083] 35 Hollow structural components

[0084] 36 Emission outlets

[0085] 40 air passages

[0086] 41 Air intake side

[0087] 42 Air output side

[0088] R Rotation axis

[0089] RA rotor plane

[0090] X radial axis (rotor blade mounting).

Claims

1. A rotor system (10) for an aircraft (1), said rotor system comprising: A drivable rotor (20) having multiple rotor blades (21) arranged radially about the rotation axis (R) of the rotor (20), and a plane perpendicular to the rotation axis (R) and passing radially through the rotor blades (21) forming a rotor plane (RA); and A rotor shield (30) surrounds the rotor (20) about the axis of rotation (R) and defines an air passage (40) of the rotor (20) extending in the axial direction along the axis of rotation (R). The rotor shroud (30) is constructed as a hollow structure (31) surrounding the axis of rotation (R). The hollow structure (31) has at least a section of a gas-permeable region (32a) on its radially facing circumferential surface (32) facing the rotor (20). The rotor plane (RA) intersects with the gas-permeable region (32a). The hollow structure (31) is configured such that sound waves of at least one frequency that pass through the gas-permeable region (32a) and enter the hollow structure (31) are at least partially absorbed by the hollow structure (31). The rotor shroud (30) includes a main structure constructed by the hollow structure (31) in conjunction with the gas-permeable region (32a) which is at least segmentally formed. The main structure forms an aerodynamic liner and an aeroacoustic liner. The cavity formed by the hollow structure extends continuously in the circumferential direction.

2. The rotor system (10) according to claim 1, wherein, The circumferential surface (33) of the hollow structure (31) opposite the gas-permeable region (32a) on the side away from the rotor blade (21) is called the outer operating inner surface. The inner side of the circumferential surface (32) having the gas-permeable region (32a) facing the outer operating inner surface is called the inner operating inner surface. The outer operating inner surface and the inner operating inner surface are spaced apart such that the gas-permeable region (32a) and the opposite circumferential surface (33) are at least sectionally configured as a λ / 4 resonator for the at least one frequency.

3. The rotor system (10) according to claim 1 or 2, wherein, The hollow structure (31) is at least sectionally configured as a Helmholtz resonator for the at least one frequency.

4. The rotor system (10) according to claim 1 or 2, wherein, The hollow structure (31) is configured to be fluid-permeable in at least the circumferentially parallel to gravity orientation in the circumferential direction.

5. The rotor system (10) according to claim 1 or 2, wherein, The hollow structure (31) has at least one discharge port (36).

6. The rotor system (10) according to claim 1 or 2, wherein, The rotor blade (21) has an angle of attack that can be variably adjusted about an axis (X) about the axis of rotation (R), and the gas-permeable region (32a) extends about the axis of rotation (R) in the axial direction at least over the region covering the rotor blade position that can be achieved via the angle of attack.

7. The rotor system (10) according to claim 1, wherein, The porosity of the gas-permeable region (32a) is between 5% and 90%.

8. The rotor system (10) according to claim 7, wherein, The porosity changes axially from the rotor plane (RA) about the axis of rotation (R).

9. The rotor system (10) according to claim 8, wherein, The porosity increases outward from the rotor plane (RA) toward at least one side.

10. The rotor system (10) according to claim 7, wherein, The porosity changes along the circumferential direction of the gas-permeable region (32a).

11. The rotor system (10) according to claim 1 or 2, wherein, The gas-permeable zone (32a) is composed of micro-perforations, perforated plates, and / or wire mesh.

12. The rotor system (10) according to claim 1 or 2, wherein, The hollow structure (31) absorbs incoming sound waves in the broadband frequency range.

13. The rotor system (10) according to claim 1 or 2, wherein, The hollow structure (31) at least partially absorbs incoming sound waves in the frequency range from 30 Hz to 1500 Hz.

14. The rotor system (10) according to claim 1 or 2, wherein, The rotor system (10) includes at least one support (22) disposed on the air intake side (41) of the rotor system (10).

15. The rotor system (10) according to claim 14, wherein, The at least one support (22) is eccentrically positioned about the axis of rotation (R).

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