CN114462257A - Flow oscillation control method for landing gear bay of aviation aircraft - Google Patents

Flow oscillation control method for landing gear bay of aviation aircraft Download PDF

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CN114462257A
CN114462257A CN202210371898.8A CN202210371898A CN114462257A CN 114462257 A CN114462257 A CN 114462257A CN 202210371898 A CN202210371898 A CN 202210371898A CN 114462257 A CN114462257 A CN 114462257A
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landing gear
flow
boundary condition
cabin
noise
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CN114462257B (en
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李博
周清清
袁先旭
刘朋欣
陈坚强
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Computational Aerodynamics Institute of China Aerodynamics Research and Development Center
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Abstract

The invention discloses a flow oscillation control method for an aircraft landing gear cabin, which comprises the steps of establishing a numerical model of the landing gear cabin, wherein the bottom of the landing gear cabin is set to be a porous material in the numerical model; determining a boundary condition; substituting the boundary conditions into a numerical model, and solving the porous wall surface flow of the bilge; calculating the radiation noise amplitude based on the porous wall surface flow data of the bilge; and evaluating the noise level, and regulating and controlling the porous wall surface parameters based on the noise level. The invention provides a flow oscillation control method for an aircraft landing gear cabin, which aims to solve the problems of configuration change, pneumatic performance damage, huge energy consumption, incapability of responding to dynamic characteristics and the like of the noise control technology for the landing gear cabin in the prior art and fulfill the aims of improving the flow environment in a cavity and inhibiting radiation noise as simple as possible on the premise of maintaining the configuration of the landing gear cabin unchanged.

Description

Flow oscillation control method for landing gear bay of aviation aircraft
Technical Field
The invention relates to the field of aircraft flow oscillation control, in particular to a flow oscillation control method for an aircraft landing gear cabin.
Background
With the rapid development of the air transportation industry and the demand for quiet flight, airborne noise becomes a critical issue that interferes with residents around airports and affects aircraft comfort. The noise of the aircraft mainly comprises body noise, engine noise and interference noise of a propulsion system and a body, wherein a landing gear system is a main source of the body noise of the commercial aircraft, the noise generated by a landing gear accounts for about 30% of the noise of the whole aircraft in the approach stage of the aircraft, and a landing gear cabin is a main source of the landing gear noise, so the control of the landing gear noise is mainly to inhibit the landing gear cabin noise.
High amplitude noise with a wide band and low frequency is radiated in the landing gear housing accompanied by strong pressure and velocity pulsations. In the prior art, the main methods for controlling the noise of the landing gear cabin comprise active control and passive control: one is a passive control method such as changing the landing gear bay configuration (such as rear corner rounding or a ramp structure) or adding vortex generators upstream; and active control methods such as applying slit jet flow on the upstream of the front edge. However, these existing control methods are only effective in a limited range of flow rates, and the passive control method can seriously deteriorate the aerodynamic performance of the landing gear bay, while the active control method of introducing excitation to the flow by installing an additional exciter consumes enormous energy and cannot respond to the dynamic characteristics of the system.
Disclosure of Invention
The invention provides a flow oscillation control method for an aircraft landing gear cabin, which aims to solve the problems of configuration change, pneumatic performance damage, huge energy consumption, incapability of responding to dynamic characteristics and the like of the noise control technology for the landing gear cabin in the prior art and fulfill the aims of improving the flow environment in a cavity and inhibiting radiation noise as simple as possible on the premise of maintaining the configuration of the landing gear cabin unchanged.
The invention is realized by the following technical scheme:
an aircraft landing gear bay flow oscillation control method comprises the following steps:
establishing a numerical model of the landing gear cabin, and setting the bottom of the landing gear cabin in the numerical model as a porous material;
determining a boundary condition;
substituting the boundary conditions into a numerical model, and solving the porous wall surface flow of the bilge;
calculating the radiation noise amplitude based on the porous wall surface flow data of the bilge;
and evaluating the noise level, and regulating and controlling the porous wall surface parameters based on the noise level.
The invention provides a flow oscillation control method of an aircraft landing gear cabin, aiming at the problems that the noise control technology of the landing gear cabin in the prior art has the defects of changing the configuration, damaging the aerodynamic performance, having huge energy consumption, being incapable of responding to the dynamic characteristics and the like, the method firstly models to obtain a numerical model of the landing gear cabin, then sets the cabin bottom of the landing gear cabin in the model as a porous material, and sets the cabin bottom formed by the porous material as the porous material, so that the fluid can be allowed to enter and exit, the flow in the cabin can be improved, and the pressure oscillation on the surface of the cavity bottom can be reduced, thereby inhibiting the feedback action of the fluid in the cabin, and inhibiting the propagation of the noise in the cabin and the development of the radiation noise outside the cabin while reducing the integral self-sustained oscillation intensity in the cabin; the test of the applicant proves that compared with the traditional solid wall which is impenetrable to the landing gear cabin, the sound pressure and the pulsation of the cabin bottom with the porous wall adopted by the application are obviously reduced, and the noise level radiated to a far field is also greatly reduced.
However, due to the strong pressure and velocity pulsation effects faced by the landing gear bay, it is still difficult to obtain a stable and effective noise reduction effect by merely replacing the bilge of the landing gear bay with a porous material; therefore, the flow oscillation control is carried out, firstly, the boundary condition of the numerical model is determined, then the boundary condition is substituted into the numerical model, the porous wall surface flow of the bilge is solved, then the radiation noise amplitude is calculated, the noise level under the boundary condition can be evaluated after the radiation noise amplitude is obtained, and then the porous wall surface parameters are regulated and controlled according to the noise level, so that the flow oscillation control is realized.
According to the method, on the premise of maintaining the configuration of the landing gear cabin unchanged, the flow in the cabin can be changed by adopting a very simple mode, so that the radiation noise is inhibited, the flow environment in the cavity is improved, and the noise level is inhibited, so that the defects that the existing control method can only be effective in a limited flow rate range, the pneumatic performance of the landing gear cabin can be seriously damaged by the existing passive control mode, the existing active control mode needs huge energy consumption, the dynamic characteristic of a system cannot be responded and the like are overcome.
Further, the boundary conditions comprise an inflow boundary condition, a far-field boundary condition, a wall boundary condition of a plane of the fuselage around the landing gear bay, a boundary condition of a computational domain boundary buffer zone, and a wall boundary condition of a porous material. Wherein the content of the first and second substances,
inflow and outflow boundary conditions: boundary conditions for flowing in and out of the computational domain in the incoming flow direction;
far-field boundary conditions: a computational domain, remote from the gear well, for simulating flow out at the boundary;
wall boundary conditions of the fuselage plane around the landing gear bay: for simulating a fuselage plane around the landing gear bay;
calculating a domain boundary buffer boundary condition: it is not reasonable that noise radiated to the far field is generated in the landing gear well due to flow oscillation, and the sound wave is likely to be reflected at the boundary of the calculation domain of the far field. In order to suppress the reflection of the sound wave by the model, a buffer area is arranged at the boundary of the calculation domain, so that the sound wave is attenuated in the buffer area;
wall boundary conditions of the porous material: a perforated wall for simulating the underbody of the landing gear.
The inflow and outflow boundary condition adopts a subsonic inflow and outflow boundary condition; research by the applicant shows that for the landing gear cabin, the flow enters and exits the calculation domain in a subsonic flow state, so that the entrance and exit flow boundary condition is set as the subsonic entrance and exit flow boundary condition.
The far field boundary condition adopts a non-reflection boundary condition to prevent the reflection of sound waves at the boundary;
the wall boundary condition of the plane of the fuselage around the landing gear cabin adopts the non-slip wall boundary condition so as to meet the condition that the flow cannot slip in the plane of the fuselage.
Further, the wall boundary condition of the porous material is a function based on porosity and back pressure.
In the scheme, the property of the porous material is determined through two parameters of porosity and backpressure, and the wall boundary condition of the porous material is defined on the basis of the property, so that a quantitative and stable basis is provided for the subsequent regulation and control process.
The wall boundary conditions of the porous material include:
Figure 415958DEST_PATH_IMAGE001
；
in the formula (I), the compound is shown in the specification,βis porosity;pis a back pressure;vis the permeation rate;p w is the wall surface pressure;ρis the fluid density;uis the flow velocity.
As can be seen from the above formula, the permeation ratevPositive correlation with porosity and back pressure, wall pressurep w A fixed value, so as the porosity becomes larger, the porous wall can allow more flow to penetrate the wall, so the permeation rate becomes larger; when back pressurepPressure with wall surfacep w When the relative value of (2) is increased, the permeation rate of the porous wall surface is also increased; on the contrary, the permeation rate of the porous wall surface becomes small. When the porosity is not changed, different permeation speeds can be obtained by adjusting the back pressure.
Further, the radiation noise amplitudedBCalculated by the following formula:
Figure 808762DEST_PATH_IMAGE002
；
in the formula (I), the compound is shown in the specification,tis the time;Tcounting the cycle length;p 0is a reference sound pressure;p(t) As instant of timetThe sound pressure of (2).
The formula can be simply understood as that the sound pressure level is obtained after time averaging to represent the amplitude of the noise.
Further, the method for regulating and controlling the parameters of the porous wall surface based on the noise level comprises the following steps:
if the noise level in the main radiation direction meets the set requirement, ending the control process;
and if the noise level of the main radiation direction does not meet the set requirement, keeping the porosity of the porous material unchanged, adjusting the back pressure, and solving the porous wall surface flow of the bilge again until the noise level of the main radiation direction meets the set requirement.
In the scheme, the mode of controlling the flow oscillation of the landing gear cabin is to keep the porosity of the porous material as a fixed value, and different permeation speeds are obtained by adjusting the back pressure of the boundary condition of the wall surface of the porous material, so that different radiation noise amplitudes are calculated.
The "setting requirement" in the present embodiment includes, but is not limited to, a set threshold, a set noise reduction value, a set noise reduction rate, and the like, and any "setting requirement" that can be conceived by those skilled in the art according to the prior art can be applied to the present application.
Further, the setting requirement is as follows: the main radiation direction noise level is reduced by at least 5 db compared to before control. In the scheme, the set noise reduction amplitude is taken as a set requirement, and the noise is reduced by more than 5 decibels, so that the regulation is considered to be effective.
Further, the porous wall surface flow of the bilge is calculated based on a finite difference method.
Further, when a numerical model of the landing gear cabin is established, the landing gear cabin is turned over in a mirror image mode along the plane of the surrounding fuselage. Those skilled in the art will appreciate that the landing gear bay opening is downward and its bilge should be at the top surface, but such a structure is more difficult to model and is not easy to understand; according to the scheme, the landing gear cabin is symmetrically overturned in a mirror image mode along the original bottom surface of the landing gear cabin, so that the landing gear cabin is changed into a mode that the opening is upward, the cabin bottom is located at the bottom and is located below the fuselage, the arrangement cannot change the flow characteristic, and the landing gear cabin has the advantages of reducing modeling difficulty, being convenient to understand and set and the like.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the flow oscillation control method for the landing gear cabin of the aviation aircraft, the cabin bottom of the landing gear cabin is made of the porous material, so that fluid can be allowed to enter and exit, the flow in the cabin can be improved, and the pressure oscillation on the surface of the cavity bottom can be reduced, so that the feedback effect of the fluid in the cabin is inhibited, the integral self-sustaining oscillation intensity in the cabin is reduced, and meanwhile, the propagation of noise in the cabin and the development of radiation noise outside the cabin are inhibited; compared with the traditional solid wall which cannot penetrate through the landing gear cabin, the sound pressure and the pulsation of the cabin bottom with the porous wall adopted by the application are obviously reduced, and the noise level radiated to a far field is also greatly reduced.
2. According to the flow oscillation control method for the landing gear cabin of the aviation aircraft, on the premise that the configuration of the landing gear cabin is kept unchanged, the flow in the cabin can be changed by adopting a very simple mode, so that the radiation noise is inhibited, the flow environment in the cavity is improved, and the noise level is inhibited, so that the defects that the existing control method can only be effective in a limited flow speed range, the pneumatic performance of the landing gear cabin can be seriously damaged by the existing passive control mode, the existing active control needs to consume huge energy, the dynamic characteristics of the system cannot be responded and the like are overcome.
3. The invention relates to a flow oscillation control method for an aircraft landing gear cabin, which keeps the porosity of a porous material as a fixed value, obtains different permeation speeds by adjusting the back pressure of the boundary condition of the wall surface of the porous material, and calculates different radiation noise amplitudes so as to realize the obvious control effect on the flow oscillation of the landing gear cabin.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic flow chart of an embodiment of the present invention;
FIG. 2 is a front view of an aircraft in accordance with an embodiment of the present invention;
FIG. 3 is a partial cross-sectional view of a landing gear bay of an aircraft in an exemplary embodiment of the invention;
FIG. 4 is a numerical model of an embodiment of the present invention;
FIG. 5 shows a back pressure of 0.85 in an embodiment of the present inventionp 0A time-middle section full-field sound pressure level distribution diagram;
FIG. 6 shows an embodiment of the present invention in which the back pressure isp 0A time-middle section full-field sound pressure level distribution diagram;
FIG. 7 shows a back pressure of 1.12 in an embodiment of the present inventionp 0A time-middle section full-field sound pressure level distribution diagram;
FIG. 8 is a graph showing a quantitative comparison of noise at arc monitoring point locations in accordance with an embodiment of the present invention;
FIG. 9 shows a back pressure of 0.85 in an embodiment of the present inventionp 0A middle section flow distribution change diagram in the time chamber;
FIG. 10 shows an embodiment of the present invention with a back pressure ofp 0A middle section flow distribution change diagram in the time chamber;
FIG. 11 shows a back pressure of 1.12 in an embodiment of the present inventionp 0The middle section flow distribution change diagram in the time chamber.
Reference numbers and corresponding part names in the drawings:
1-landing gear bay, 2-porous material.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention. In the description of the present application, it is to be understood that the terms "front", "back", "left", "right", "upper", "lower", "vertical", "horizontal", "high", "low", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, merely for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore, should not be construed as limiting the scope of the present application.
Example 1:
a method for controlling the flow oscillations of an aircraft landing gear bay as shown in fig. 1, comprises the following steps:
establishing a numerical model of the landing gear cabin, and setting the bottom of the landing gear cabin in the numerical model as a porous material;
determining a boundary condition;
substituting the boundary conditions into a numerical model, and solving the porous wall surface flow of the bilge;
calculating the radiation noise amplitude based on the porous wall surface flow data of the bilge;
evaluating the noise level, and regulating and controlling the porous wall surface parameters based on the noise level:
if the noise level in the main radiation direction meets the set requirement, ending the control process;
if the noise level in the main radiation direction does not meet the set requirement, the porosity of the porous material is maintainedβConstant, regulated back pressurepAnd solving the porous wall surface flow of the cabin bottom again until the noise level of the main radiation direction meets the set requirement.
The boundary conditions comprise an inflow boundary condition, a far-field boundary condition, a wall boundary condition of a plane of a fuselage around the landing gear cabin, a boundary condition of a calculation domain boundary buffer zone and a wall boundary condition of a porous material.
Example 2:
a method for controlling the flow oscillation of an aircraft landing gear cabin takes a typical M219-type landing gear cabin as a research object, and the landing gear cabin and a corresponding aircraft are shown in figures 2 and 3. In this landing gear bay configuration, the length: width: the depth is 5:1: 1. When mach number Ma =0.85, reynolds number Re =0.6 × 107Flow through this configuration creates a typical self-sustaining oscillatory phenomenon.
The present embodiment first models the landing gear bay configuration in figure 3 into the model shown in figure 4. The symmetry of the landing gear bay with the opening facing downwards with respect to the horizontal plane is changed into the symmetry with the opening facing upwards in the modeling process, so that the model shown in fig. 4 is obtained, and the arrangement can reduce the modeling difficulty and can not change the flow characteristics.
Then determining boundary conditions, wherein the boundary conditions are divided into wall surface boundary conditions of the porous material and the rest boundary conditions; the remaining boundary conditions are first determined as follows:
a) ingress and egress stream boundaries, i.e. the boundaries denoted by sequence number c in fig. 4: boundary conditions of flowing in and out of a calculation domain in the incoming flow direction are selected, and the boundary conditions of subsonic velocity flowing in and out are selected in the subsonic velocity flowing state;
b) far-field boundary conditions, i.e., the boundary denoted by the number (r) in fig. 4: a calculation domain remote from the gear well, where the flow is primarily simulated to flow out of the calculation domain and where reflections of sound waves at the boundary are to be prevented;
c) no slip wall boundary condition, i.e., boundary represented by number # in fig. 4: simulating a plane of the aircraft body around the landing gear cabin, wherein the plane of the aircraft body cannot slide when flowing, and adopting a boundary condition of a non-sliding wall surface;
d) buffer, i.e. the boundary indicated by the number (c) in fig. 4: noise radiated to the far field due to flow oscillations in the landing gear bay may be emitted unreasonably at the far field computation domain boundaries. To suppress the reflection of the acoustic wave, a buffer is arranged at the boundary of the calculation domain so that the acoustic wave is attenuated in the buffer.
Then, the boundary conditions of the porous wall, i.e. the serial number in FIG. 4, capable of simulating the porous material are set in the numerical model
Figure 863306DEST_PATH_IMAGE003
The boundaries are shown, i.e. shaded in fig. 4. The boundary condition of the porous wall surface determines the property of the porous material through two parameters, namely the porosityβAnd back pressurep. In this embodiment, the control effect is only adjusted by the back pressure, so the porosity is first adjustedβSet to empirical value (porosity)β= 11.2%), by adjusting the back pressure of the perforated bilgepVarying the permeation rate at the porous bilge wallv：
Figure 14189DEST_PATH_IMAGE001
In the formula (I), the compound is shown in the specification,βis porosity;pis a back pressure;vis the permeation rate;p w is the wall surface pressure;ρis the fluid density;uis the flow velocity.
As the porosity becomes larger, the porous wall can allow more flow to penetrate the wall, so the permeation rate becomes larger; when back pressurepPressure with wall surfacep w When the relative value of (2) is increased, the permeation rate of the porous wall surface is also increased; on the contrary, the permeation rate of the porous wall surface becomes small.
All boundary conditions determined above are then brought into the numerical model and the porous wall flow is solved. In the embodiment, a computational model based on a finite difference method is adopted for solving, and the solving process follows a fluid control equation.
And then analyzing the flow data obtained by the solving result, and calculating the radiation noise amplitude, wherein the noise calculation formula is as follows:
Figure 786973DEST_PATH_IMAGE002
；
in the formula (I), the compound is shown in the specification,p 0for reference sound pressure, 2 × 10 is taken in this example-5Pa；p(t) Instantaneous sound pressure;tis the time;Tthe statistical period length.
Finally, whether the noise level of the main radiation direction is reduced by more than 5 decibels is evaluated;
if the requirements are satisfied, the optimization control of the present embodiment is ended.
And if the requirements are not met, continuously adjusting the back pressure of the porous bilge in the wall boundary conditions of the porous material, recalculating the porous wall flow, and carrying out noise level evaluation again until the requirements are met.
The simulation results of this example show that:
referring to fig. 5 to 7, the abscissa of fig. 5 to 7 represents the flow direction position of the landing gear bay, and the ordinate represents the vertical positionThe normal position of the landing gear cabin and the coordinate origin are at the vertex of the front edge of the landing gear cabin, wherein the backpressure is 0.85 as shown in each of the figures 5, 6 and 7p 0、p 0And 1.12p 0The full field sound pressure level distribution of the time-intermediate section. As can be seen from fig. 5 to 7, the cabin bottom sound pressure and pulsation of the perforated wall are significantly reduced, and the noise level radiated to the far field is also significantly reduced, compared to the case where the landing gear cabin bottom is a solid wall that is not impermeable to sliding.
FIG. 8 shows a back pressure of 0.85p 0、p 0And 1.12p 0Quantitative comparison of the noise at the arc monitor point location for three cases, where (a) represents a backpressure of 0.85p 0And (b) the back pressure isp 0And (c) a back pressure of 1.12p 0。
The abscissa of fig. 8 is noise (in decibels) and the ordinate is the radiation direction (in °); the change in sound pressure level can be more clearly reflected from fig. 8.
In addition, referring to fig. 9 to 11, the abscissa of fig. 9 to 11 represents the flow direction position of the landing gear bay, the ordinate represents the normal position of the landing gear bay, the origin of the coordinates is at the apex of the nose of the landing gear bay, and fig. 9 to 11 each represent a backpressure of 0.85p 0、p 0And 1.12p 0The mid-section flow distribution within the chamber varies. As can be seen from fig. 9 to 11, compared with the case that the bottom of the landing gear is a solid wall which is not penetrated by slip, the flow in the cabin is obviously improved and the shear layer is obviously raised after the control by the method of the present application.
In summary, the flow control of the present embodiment effectively suppresses landing gear bay noise levels and improves intra-bay flow, successfully reduces landing gear noise, and does not change the configuration of the landing gear bay.
Example 3:
an aircraft landing gear bay flow oscillation control system based on the oscillation control method of any one of the embodiments comprises:
the modeling module is used for establishing a numerical model of the landing gear cabin and setting the bottom of the landing gear cabin in the numerical model as a porous material;
a boundary module for determining a boundary condition;
the calculation module is used for calculating the porous wall surface flow of the cabin bottom and the corresponding radiation noise amplitude;
and the control module is used for regulating and controlling the parameters of the porous wall surface according to the noise level.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
It should be noted that, in this document, terms such as "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, the term "connected" used herein may be directly connected or indirectly connected via other components without being particularly described.

Claims (10)

1. A method for controlling flow oscillation of an aircraft landing gear bay is characterized by comprising the following steps:
establishing a numerical model of the landing gear cabin, and setting the bottom of the landing gear cabin in the numerical model as a porous material;
determining a boundary condition;
substituting the boundary condition into a numerical model to solve the porous wall surface flow of the bilge;
calculating the radiation noise amplitude based on the porous wall surface flow data of the bilge;
and evaluating the noise level, and regulating and controlling the porous wall surface parameters based on the noise level.
2. The method of claim 1, wherein the boundary conditions include an inflow boundary condition, a far field boundary condition, a wall boundary condition of a plane of a fuselage surrounding the landing gear bay, a computational domain boundary buffer boundary condition, and a wall boundary condition of a porous material.
3. The method of claim 2, wherein the inflow boundary condition is a subsonic inflow boundary condition; the far field boundary condition adopts a non-reflection boundary condition; the wall boundary condition of the plane of the fuselage around the landing gear bay adopts a non-slip wall boundary condition.
4. The method of claim 2, wherein the wall boundary condition of the porous material is a function based on porosity and backpressure.
5. The method of claim 4, wherein the wall boundary conditions of the porous material comprise:
Figure 246876DEST_PATH_IMAGE001
；
in the formula (I), the compound is shown in the specification,βis porosity;pis a back pressure;vis the permeation rate;p w is the wall surface pressure;ρis the fluid density;uis the flow velocity.
6. An aircraft landing gear bay flow oscillation control method according to claim 1, wherein the radiated noise amplitude is greater than the radiated noise amplitudedBCalculated by the following formula:
Figure 547408DEST_PATH_IMAGE002
；
in the formula (I), the compound is shown in the specification,tis the time;Tcounting the cycle length;p 0is a reference sound pressure;p(t) As instant of timetThe sound pressure of (2).
7. The method of controlling flow oscillations in an aircraft landing gear bay according to claim 5, wherein the method of modulating the porous wall parameters based on the noise level comprises:
if the noise level in the main radiation direction meets the set requirement, ending the control process;
if the noise level in the main radiation direction does not meet the set requirement, the porosity of the porous material is maintainedβConstant, regulated back pressurepAnd solving the porous wall surface flow of the cabin bottom again until the noise level of the main radiation direction meets the set requirement.
8. An aircraft landing gear bay flow oscillation control method according to claim 7, wherein the set requirements are: the noise level in the main radiation direction is reduced by at least 5 db compared to before control.
9. The method according to claim 1, wherein the porous wall flow of the bilge is calculated based on a finite difference method.
10. A method of controlling flow oscillations in an aircraft landing gear bay according to claim 1, wherein said landing gear bay is mirror-inverted along a surrounding fuselage plane when a numerical model of the landing gear bay is established.
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