A method and system for reducing the radiated noise of a blunt body based on active flow control

Abstract

A method and system for reducing the radiation noise of a bluff body based on active flow control, belonging to the fields of fluid mechanics, flow control, and flow noise; the method steps are as follows: obtaining hydrodynamic information and sound pressure information at the observation point through numerical simulation; based on the obtained information, designing an active flow control parameter combination and obtaining the response of the bluff body to the active flow control; setting the control parameters according to the obtained control response, that is, configuring the phase of the active flow control, and obtaining the noise reduction effect of the control through the phase cancellation interference between sound signals. This method uses active flow control to regulate the phases of noise sources from different bluff bodies, making the sound waves emitted by them cancel each other out, and finally achieving the effect of reducing the radiation noise at the observation point without significantly changing the hydrodynamic force received by the bluff body.

Description

Technical Field

[0001] The present invention belongs to the fields of fluid mechanics, flow control, and flow noise, and particularly relates to a method and system for reducing blunt body radiation noise based on active flow control. Background Art

[0002] The problem of blunt body flow-induced radiation noise widely exists in life. For example, the landing gear of an aircraft, the appendages of an underwater vehicle, and the rearview mirror of a car will radiate noise outward during movement. Especially when there is blunt body flow around multiple components, the overall radiation noise will increase significantly. Acoustic researchers usually use active control or passive control to reduce radiation noise, such as setting sound insulation and sound absorption materials and introducing secondary sound sources for destructive interference to control noise during the sound propagation process. For example, Chinese Patent No. CN209351388U, titled "Filtering Device, Filtering Method and Active Noise Canceling Headphone", uses a microphone to collect noise signals and an internal speaker to generate sound waves with opposite phases to cancel the noise. Acoustic passive control usually only has a noise reduction effect on sound waves within a specific frequency range due to structural size limitations, while acoustic active control requires matching time-domain signals and has strict requirements for algorithms.

[0003] In addition to reducing noise during sound propagation, since the noise source is closely related to fluid dynamics, researchers in the fields of fluid mechanics or flow noise mainly focus on reducing noise from the source perspective. For example, by changing the shape of the blunt body, setting up vortex breakdown devices, applying rotational control, etc. to intervene in the flow field structure, and then changing the radiation noise characteristics in the far field. The prior art discloses a noise reduction system applying plasma flow control. It adopts an active flow control method. Through a plasma generating device, the flow separation on the train surface is delayed, the turbulent pulsation intensity is reduced, and the noise is suppressed. However, the above noise reduction methods based on weakening the source intensity usually involve changes in the flow field structure, resulting in changes in fluid dynamic parameters such as lift and drag forces on the blunt body. In engineering design, it is necessary to comprehensively consider fluid dynamics and noise, which increases the design difficulty. Existing research has shown that flow control can not only change the frequency and amplitude of the sound source, but also effectively control the phase of the sound source. However, the research on intervening in the phase of the sound source through active flow control and using sound waves with different phase characteristics emitted from different sound sources for destructive interference has not been publicly reported. Summary of the Invention

[0004] Technical Problems to be Solved:

[0005] To avoid the deficiencies of the prior art, the present invention provides a method and system for reducing the radiation noise of a bluff body based on active flow control. This method uses active flow control to regulate the phases of noise sources from different bluff bodies, causing the emitted sound waves to cancel each other out, and ultimately achieving the effect of reducing the radiation noise at the observation point without significantly changing the hydrodynamic forces acting on the bluff body.

[0006] The technical solution of the present invention is as follows: A method for reducing the radiation noise of a bluff body based on active flow control, and the specific steps are as follows:

[0007] Step 1: Obtain hydrodynamic force information and sound pressure information at the observation point through numerical simulation;

[0008] Step 2: Based on the information obtained in Step 1, design a combination of active flow control parameters and obtain the response of the bluff body to the active flow control;

[0009] Step 3: Set the control parameters according to the control response obtained in Step 2, that is, configure the phase of the active flow control, and obtain the noise reduction effect of the control through the phase cancellation interference between sound signals.

[0010] A further technical solution of the present invention is: In Step 1, the lattice Boltzmann method with low dispersion and low dissipation is used to solve the flow control equation to obtain accurate hydrodynamic force information and sound pressure information at the observation point; the hydrodynamic force information includes the frequency and amplitude of the lift force on the surface of the bluff body.

[0011] A further technical solution of the present invention is: In Step 1, the hydrodynamic force information, that is, the frequency and amplitude of the lift force on the surface of the bluff body, is calculated as follows:

[0012]

[0013]

[0014] Among them, f represents the characteristic frequency obtained by performing a fast Fourier transform calculation on the lift force signal on the surface of the bluff body, and F 2 represents the lift force obtained by performing a fast Fourier transform calculation on the lift force signal on the surface of the bluff body, ρ 0 represents the fluid density, L 0 represents the diameter of the bluff body; U 0 represents the incoming flow velocity;

[0015] The sound pressure information at the observation point is p′, p′ = p - p mean , where p is the instantaneous pressure fluctuation at the observation point, and p mean is the average pressure at the observation point.

[0016] A further technical solution of the present invention is as follows: in step 1, during the flow control calculation process, an acoustic absorption layer is added to dissipate the sound waves in the area outside the observation point, avoiding the reflection of sound waves by the boundary of the computational domain; at the same time, a graphics processing unit (GPU) is used to parallelize and accelerate the solution method.

[0017] A further technical solution of the present invention is as follows: in step 2, the active flow control parameters are the amplitude, frequency, and phase of the sine signal; the control strategy velocity U sj is a periodic sine signal, and the relationship is as follows:

[0018] U sj = A sj sin(2πf sj t + ΔΦ sj )

[0019] where A sj is the amplitude of the sine signal, f sj is the frequency of the sine signal, ΔΦ sj is the phase of the sine signal; t is the time;

[0020] The response θ of the bluff body to the active flow control is the difference between the hydrodynamic phase and the phase of the control strategy.

[0021] A further technical solution of the present invention is as follows: the method for obtaining the response θ of the bluff body to the active flow control is as follows. First, apply active flow control to the bluff body and design different combinations of parameters of amplitude A sj , frequency f sj , and phase ΔΦ sj . Then, substitute the designed different combinations of active flow control parameters into the formula in step 1, and through numerical simulation, calculate the instantaneous lift pulsation curve on the surface of the bluff body after applying the control. Among them, the phase is adjusted by starting at different times within a period T 0 , and according to T 0 = 2π / f 0 calculate its corresponding period T 0 . Finally, perform a fast Fourier transform on the instantaneous lift pulsation curve on the surface of the bluff body obtained in the previous step to obtain the amplitude, frequency, and response phase θ of the lift pulsation of the bluff body.

[0022] A further technical solution of the present invention is as follows: the method for setting the control parameters in step 3 is as follows. First, select the amplitude and frequency that can achieve frequency locking, and the phase can be arbitrarily selected. Then, input the control strategy corresponding to the selected control parameters into step 1, and through numerical simulation, calculate the corresponding hydrodynamic change curve. Finally, obtain the instantaneous sound pressure pulsation at the far-field observation point.

[0023] A further technical solution of the present invention is that the principle for selecting the amplitude in the control parameters is to select the minimum control amplitude on the premise of ensuring frequency locking, so as to reduce energy consumption and reduce the self-noise of active flow control.

[0024] A further technical solution of the present invention is that in the step 3, the relationship between the control parameters and the total lift Γ on the bluff body surface is as follows:

[0025]

[0026] where C* L,k is the lift amplitude in the control parameters, ΔΦ* sj is the control phase in the control parameters, θ k * is the response phase in the control parameters; k represents the k-th bluff body;

[0027] Reducing the total lift can reduce the radiation noise at the observation point.

[0028] A system for implementing a method for reducing the radiation noise of a bluff body based on active flow control includes a flow field solution module and an active flow control module. The flow field solution module is used to obtain hydrodynamic information and the sound pressure information at the observation point, and the active flow control module is used to output the hydrodynamic pulsation for controlling the flow field;

[0029] The flow field solution module uses numerical simulation to calculate the hydrodynamic information and the sound pressure information, including the information without applying active flow control and the information with applying active flow control;

[0030] The active flow control module includes jet holes arranged on a plurality of bluff bodies. Two jet holes are symmetrically arranged on a single bluff body, and the fluid velocity directions in the two jet holes are opposite, that is, blowing up and sucking down or sucking down and blowing up; the hydrodynamic pulsation output by the active flow control module enables the phase cancellation interference between the sound signals on the bluff body surface, so as to achieve the purpose of reducing the noise at the observation point.

[0031] Beneficial effects

[0032] The beneficial effects of the present invention are as follows:

[0033] 1. Based on the phase characteristics of the common frequency locking phenomenon in the field of flow control, that is, when frequency locking occurs, the phase of the noise generated by the hydrodynamic pulsation is also correspondingly determined. Therefore, without complex signal processing means, the phases of each sound source can be determined.

[0034] 2. Through the phase cancellation interference between the sound signals, the present invention can achieve a significant noise reduction effect.

[0035] 3. When the present invention is near the natural frequency of the bluff body, slight control can cause frequency locking, and the noise reduction method is easy to implement.

[0036] 4. The control amplitude applied in the present invention is usually small, and the control principle does not reduce the sound source intensity by changing the flow field characteristics, so it will not cause significant changes to the fluid dynamics.

[0037] 5. The present invention uses numerical simulation methods to obtain the fluid dynamic information and sound pressure information acting on the surface of the bluff body, which should not only accurately solve the fluid dynamic information, but also reduce the error during the sound wave propagation process.

[0038] 6. The present invention can be applied to the radiation noise control of multiple bluff bodies without significantly changing the fluid dynamics acting on the bluff bodies. Description of the Drawings

[0039] Figure 1 Schematic diagram of applying active flow control to multiple bluff bodies;

[0040] Figure 2 Schematic diagram of the sound field calculation results and the observation point positions obtained by the lattice Boltzmann method in the invention;

[0041] Figure 3 Comparison of the lift force before and after applying control;

[0042] Figure 4 Comparison of the sound pressure at the measurement point before and after applying control, that is, the control effect in the present invention. Detailed Embodiment

[0043] The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0044] In this embodiment, a method and system for reducing the radiation noise of a bluff body based on active flow control are provided. This method uses active flow control to regulate the phases of the noise sources from different bluff bodies so that the emitted sound waves cancel each other out, and finally, without significantly changing the fluid dynamics acting on the bluff body, the effect of reducing the radiation noise at the observation point is achieved. The specific steps are as follows:

[0045] S1: Obtain the fluid dynamic information and the sound pressure information of the observation point through numerical simulation.

[0046] Obtaining accurate hydrodynamic information acting on the surface of a bluff body is the key to regulating the phase of the noise source using active flow control. Since it is difficult to avoid introducing additional noise sources and causing phase measurement errors in experiments, numerical simulation is used to obtain hydrodynamic and sound pressure information. Among them, the numerical simulation method should not only be able to accurately solve the hydrodynamic information but also reduce the error during the propagation of sound waves. Therefore, the lattice Boltzmann method with low dispersion and low dissipation is used to solve the flow control equation to obtain accurate hydrodynamic information and sound pressure information at the observation point. At the same time, in order to avoid the reflection of sound waves by the computational domain boundary, an acoustic absorption layer needs to be added to dissipate the sound waves in the area outside the observation point. In order to obtain results quickly, a graphics processing unit (GPU) is used to parallelize and accelerate the solution method.

[0047] Define the sound pressure as p’ = p - p mean , that is, the sound pressure is obtained by subtracting the mean pressure from the instantaneous pressure fluctuation at the observation point. Further, the lift information on the surface of the bluff body is extracted, and the fast Fourier transform is performed on the lift signal to obtain the frequency and amplitude of the lift. The following formula is used for non-dimensionalization

[0048]

[0049]

[0050] where ρ 0 is the fluid density, f and F 2 are the calculated characteristic frequency and lift respectively. Using the GPU to parallelize and accelerate the numerical solution of the flow control equation, finally, the frequency, amplitude of the lift on the surface of the bluff body and the instantaneous sound pressure fluctuation at the far-field measurement point can be obtained.

[0051] S2: According to the results of S1, design the parameter combination of active flow control and obtain the response of the bluff body to active flow control.

[0052] The specific implementation methods of active flow control include but are not limited to synthetic jet control, rotation control, vibration control, etc. The control strategy is selected as a periodic sine signal,

[0053] U sj = A sj sin(2πft + ΔΦ sj t + ΔΦ sj ) (1)

[0054] Therefore, it is necessary to determine the amplitude A sj , frequency f sj and phase ΔΦ sjand other information. Using the hydrodynamic information calculated in Step 1, the amplitude and frequency characteristics of the hydrodynamic pulsation of the bluff body without control can be obtained through fast Fourier transform. Based on the above characteristics, the amplitude and frequency of the control are selected. The phase of the control can be adjusted by turning on at different times within a period T 0 According to T 0 = 2π / f 0 to calculate its corresponding period T 0 .

[0055] Since the present invention is used on multiple bluff bodies with the same external dimensions, it is only necessary to calculate the active flow control for any one of the bluff bodies.

[0056] The flow control is achieved by modifying the boundary conditions during the flow field solution, and all combinations of control parameters are traversed. Repeat Step 1 to obtain the instantaneous lift pulsation curve on the bluff body surface. Perform fast Fourier transform on it to obtain its corresponding frequency, amplitude, and phase information, and define the difference between the hydrodynamic phase and the phase of the control strategy as the response phase θ under this combination of control parameters.

[0057] Through Step S2, finally, the amplitude, frequency, and response phase θ of the lift pulsation of the bluff body after applying different amplitude, frequency, and phase controls are obtained.

[0058] S3: Set the control parameters according to the results of Step S2, and obtain the noise reduction effect of the control through numerical simulation.

[0059] The intervention of the flow control on the hydrodynamic phase stems from the lock-in phenomenon. After the lock-in occurs, the response phase of the bluff body under the same control amplitude and frequency is also uniquely determined. The lock-in is mainly related to the amplitude and frequency of the control and has nothing to do with the phase of the control. Therefore, it is necessary to determine the range of changes in the amplitude and frequency of the control corresponding to the lock-in according to the results of Step 2. Usually, when the control frequency is close to the natural frequency of the bluff body, only a small intensity of control is required to achieve lock-in. In order to reduce energy consumption and the self-noise of the active flow control, a small control amplitude should be selected as much as possible on the premise of ensuring lock-in.

[0060] After the amplitude and frequency of the control are selected, the response phase of the bluff body is also determined. Therefore, the hydrodynamic phase on the bluff body surface will also change with the phase of the control. At low flow velocities, according to Curle's equation

[0061]

[0062] where the subscript i represents each direction of the coordinate system, 1 is the downstream direction, 2 is the direction perpendicular to the flow direction, r is the distance between the sound source and the observation point, x i is the component of r in the i direction, Fi is the force exerted on the bluff body by the fluid in the i direction. The hydrodynamic pulsation is the main sound generation mechanism, so the phase of the noise source also changes with the phase of the hydrodynamic force. By changing the phase of the flow control acting on different bluff bodies, the phase of the generated noise can be adjusted accordingly. By setting the corresponding control phases on different bluff bodies, the total lift Γ is minimized, that is

[0063]

[0064] where the subscript k represents the k-th bluff body. Finally, configure the phase of the active flow control to achieve the purpose of reducing the noise at the observation point through the destructive interference of the phases between the sound signals.

[0065] Repeat the process of step S1, use GPU parallel acceleration to numerically solve the flow control equation, and finally the instantaneous sound pressure pulsation at the far-field measurement point after applying this method for flow control can be obtained. By comparing with the instantaneous sound pressure pulsation before applying the control, the noise reduction effect can be evaluated.

[0066] A system for reducing the radiation noise of a bluff body based on active flow control in this embodiment: includes a flow field solution module and an active flow control module. The flow field solution module is used to obtain hydrodynamic information and the sound pressure information at the observation point. The active flow control module is used to output the hydrodynamic pulsation for controlling the flow field;

[0067] The flow field solution module uses numerical simulation to calculate the hydrodynamic information and the sound pressure information, including the information without applying active flow control and the information with applying active flow control;

[0068] The active flow control module includes jet holes arranged on multiple bluff bodies. Two jet holes are symmetrically arranged on a single bluff body, and the fluid velocity directions in the two jet holes are opposite, that is, blowing up and sucking down or sucking down and blowing up. The destructive interference of the phases between the sound signals on the surface of the bluff body is caused by the hydrodynamic pulsation output by the active flow control module to achieve the purpose of reducing the noise at the observation point.

[0069] Embodiment:

[0070] Take the cylinders arranged side by side as the research object bluff body to elaborate on the technical solution of the present invention in detail. Two cylinders with a diameter of L 0 are arranged side by side perpendicular to the flow direction, as Figure 1 shown, and the distance between the centers of the cylinders is 1.2L 0 .

[0071] S1: Conduct numerical simulation under two-dimensional conditions to obtain the hydrodynamic information and the sound pressure information at the observation point.

[0072] Taking the center of the lower cylinder as the origin, the flow direction as the x-axis, and the direction perpendicular to the flow direction as the y-axis, the fluid flows uniformly from left to right along the x-axis at a velocity U 0 along the x-axis. The hydrodynamic force exerted on the cylinder in the x-axis direction is defined as the drag force, and the hydrodynamic force in the y-axis direction is defined as the lift force. The sound pressure observation point is set directly above the cylinder, i.e., at the position (0, 70L 0 ). To accurately obtain the hydrodynamic force information and the sound pressure information at the observation point, the lattice Boltzmann method is used to numerically solve the flow field, and the far-field radiation noise can be obtained by post-processing the results of the flow field calculation. The computational domain is 200L 0 ×200L 0 , with a velocity boundary condition at the inlet and a pressure boundary condition at the outlet. The boundary conditions for the upper and lower walls of the computational domain are free-slip boundaries. The governing equations for the flow are the classical weakly compressible Navier-Stokes equations

[0073]

[0074] where u, p, and Re are the velocity, pressure, and Reynolds number in the flow field, respectively.

[0075] By inputting the Reynolds number Re = 100 and setting the size of the computational domain, the boundary conditions, and the position of the cylinder as required above, the instantaneous velocity u and pressure p at a fixed position in the flow field can be obtained. The lift force on the cylinder surface is calculated using the following formula

[0076]

[0077] where S is the cylinder surface, μ is the fluid viscosity, n is the unit normal vector, and the subscripts i = 1, 2 represent the components in the x and y directions, respectively.

[0078] The sound pressure is defined as p’ = p - p mean , where p mean is the average sound pressure obtained from the instantaneous sound pressure curve. It is nondimensionalized using p’ / (ρ 0 c 0 2 ), where ρ 0 is the fluid density and c 0 is the speed of sound. That is, the sound pressure is obtained by subtracting the average pressure from the instantaneous pressure fluctuation at the observation point. The calculation results are as Figure 2 shown. The far-field radiation noise of the tandem cylinders exhibits a dipole characteristic and mainly radiates sound waves from the cylinders perpendicular to the flow direction. Therefore, the lift force fluctuation on the cylinder surface is the main source of its noise generation. Further, the lift force information on the cylinder surface is extracted and subjected to a fast Fourier transform to obtain the frequency and amplitude of the lift force. The following formula is used for nondimensionalization

[0079]

[0080] Among them, f and F 2 are the calculated characteristic frequency and lift force respectively. After non-dimensionalization, it can be obtained that at a Reynolds number of 100, the characteristic frequency of the lift force is f 0 = 0.162, and the amplitude of the pulsation of the total lift force Γ of the upper and lower cylinders is |C L | max = 0.579. Through Step 1, the instantaneous sound pressure pulsation at the observation point and the frequencies and amplitudes of the cylinder lift force pulsation are finally obtained.

[0081] S2: According to the results of Step 1, taking synthetic jet control as an example, design the combination of active flow control parameters and obtain the response of a single cylinder to active flow control.

[0082] Apply synthetic jet control to the cylinder surface. Two synthetic jet holes are set for each cylinder, and the positions of the jet holes are symmetric about the y = 0 center line passing through the center of the cylinder. During the numerical simulation process, the jet control is realized by modifying the cylinder boundary conditions, that is, the velocity of the cylinder surface at the position of the jet hole changes from 0 to U sj . The direction of the jet is the same as the flow direction, and the control strategy at the position of the jet hole is that the velocity U sj varies periodically with a sine signal

[0083] U sj = A sj sin(2πft + ΔΦ sj t + ΔΦ sj ) (7)

[0084] Therefore, the parameters of synthetic jet control mainly include the amplitude A sj , the frequency f sj and the phase ΔΦ sj . In order to minimize the self-noise of the synthetic jet, it is necessary to ensure that the velocity directions of the upper and lower jet holes of a single cylinder are opposite, that is, blowing up and sucking down or sucking down and blowing up, and the velocity directions of the jet holes are set as shown in Figure 1 .

[0085] Since the sizes of the upper and lower cylinders and the oncoming flow conditions are the same in this example, only a single cylinder needs to be verified. Input the amplitude A sj , the frequency f sj and the phase ΔΦ sj to the flow field solver in Step 1, and the instantaneous lift force pulsation curve of the cylinder after applying the control can be obtained. Specifically, the amplitude A of the jet control sj is selected as 2, 3, 4 times the oncoming flow velocity U 0 , and the jet frequency f sj varies in the range of 0.8 - 2.4 times of f 0 . The phase is selected for one period T 0Compare at four internal moments, 0, 0.5π, π, 1.5π, where the period T 0 can be obtained from T 0 = 2π / f 0 by conversion. Performing a fast Fourier transform on the lift pulsation yields its amplitude C L , frequency, and phase. Define the difference between the lift pulsation phase and the phase Δφ of synthetic jet control sj as the response phase θ for this control parameter combination.

[0086] Since the main focus in step 2 is on the influence of flow control on the flow field, the computational domain is reduced to 60L 0 ×20L 0 , with a single cylinder placed 20L from the inlet 0 and 10L from the upper wall 0 . Usually, when the control frequency is close to the natural frequency of the bluff body, frequency locking can be achieved with a relatively small control amplitude. To reduce energy input, a small control amplitude A sj should be selected while ensuring frequency locking.

[0087] By numerically simulating different combinations of control parameters, the minimum jet amplitude A* sj = 2U 0 at which frequency locking can occur is finally determined, along with the corresponding jet frequency f* sj = f 0 . By performing a fast Fourier transform on the lift pulsation curve, the lift pulsation amplitude C* L of the cylinder after applying the control and the response phase θ* can be obtained.

[0088] S3: Design the control parameters for multiple cylinders based on the results of step 2 and obtain the noise reduction effect of the control through numerical simulation.

[0089] The relationship between the sound pressure at the far-field observation point and the lift on the cylinder surface can be described by the Curle equation at low flow velocities,

[0090]

[0091] where r is the distance between the sound source and the observation point. According to formula (8), reducing the total lift can lower the radiated noise at the observation point.

[0092] Therefore, when designing the control strategy for the upper and lower cylinders, the goal of reducing the sound pressure at the observation point is equivalent to reducing the total lift. At the same time, since the instantaneous lift pulsation curve of each cylinder is determined after frequency locking occurs, the total lift magnitude can be determined simply by the linear combination of the lift amplitude and the response phase, i.e.,

[0093]

[0094] When Γ decreases, the noise at the observation point also decreases. For two juxtaposed cylinders, since the upper and lower cylinders have the same size, the calculated response phase θ is also the same. Therefore, it is only necessary to ensure that the jet phases at the corresponding positions of the upper and lower cylinders are opposite.

[0095] According to the result of Step 2, the control parameter selects the amplitude A* sj = 2U 0 and the frequency f* sj = f 0 when frequency locking can be achieved. Since the response phase is independent of the control phase ΔΦ sj ΔΦ* sj can be arbitrarily selected, that is, the jet can be turned on at any time after the cylinder wake stabilizes. Input the control strategy corresponding to this control parameter into Step 1. Through numerical simulation, the corresponding hydrodynamic changes can finally be obtained as Figure 3 shown. It can be found from the figure that the amplitude and frequency of the lift pulsation of the upper and lower cylinders change little, but the phase changes from in-phase before control to out-of-phase. Therefore, the total lift Γ of the upper and lower cylinders is significantly reduced. Finally, the instantaneous sound pressure change at the far-field observation point is obtained as Figure 4 . It can be found from the figure that the sound pressure after control is much smaller than that before control. Based on the noise reduction method disclosed in the present invention, the sound pressure at the observation point is reduced by about four orders of magnitude.

[0096] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principle and spirit of the present invention.

Claims

1. A method for reducing the radiation noise of a blunt body based on active flow control, characterized in that the specific steps are as follows: Step 1: Obtain hydrodynamic information and sound pressure information at the observation point through numerical simulation; Step 2: Based on the information obtained in Step 1, design a combination of active flow control parameters and obtain the response of the blunt body to active flow control; Step 3: Set the control parameters according to the control response obtained in Step 2, that is, configure the phase of active flow control, and obtain the noise reduction effect of the control through the phase cancellation interference between sound signals; In the said Step 1, the lattice Boltzmann method with low dispersion and low dissipation is used to solve the flow control equation to obtain accurate hydrodynamic information and sound pressure information at the observation point; the hydrodynamic information includes the frequency and amplitude of the lift force on the surface of the blunt body; In the said step 2, the active flow control parameters are the amplitude, frequency and phase of the sine signal; the control strategy speed is a periodic sine signal, and the relationship is as follows: U sj = A sj sin(2πf sj t + ΔΦ sj ) wherein, is the amplitude of the sine signal, is the frequency of the sine signal, is the phase of the sine signal; t is the time; The response of the bluff body to active flow control θ is the difference between the hydrodynamic phase and the phase of the control strategy; The method for setting the control parameters in the said Step 3 is as follows: First, select the amplitude and frequency that can achieve frequency locking, and the control phase can be arbitrarily selected; then, input the control strategy corresponding to the selected control parameters into Step 1, and through numerical simulation, calculate the corresponding hydrodynamic change curve; finally, obtain the instantaneous sound pressure pulsation at the far-field observation point.

2. The method for reducing the radiation noise of a blunt body based on active flow control according to claim 1, characterized in that: In the said Step 1, the hydrodynamic information, that is, the frequency and amplitude of the lift force on the surface of the blunt body, is calculated as follows: Among them, f represents the characteristic frequency obtained by performing a fast Fourier transform calculation on the lift signal on the surface of the bluff body, F 2 represents the lift obtained by performing a fast Fourier transform calculation on the lift signal on the surface of the bluff body, ρ 0 represents the fluid density, L 0 represents the diameter of the bluff body; U 0 represents the oncoming flow velocity; The sound pressure information of the observation point is , = p - pmean, where p is the instantaneous pressure fluctuation of the observation point and pmean is the average pressure of the observation point.

3. The method for reducing the radiation noise of a blunt body based on active flow control according to claim 2, characterized in that: In the said Step 1, during the flow control calculation process, an acoustic absorption layer is added to dissipate the sound waves in the area outside the observation point to avoid the reflection of sound waves at the boundary of the calculation domain; at the same time, a graphics processing unit (GPU) is used to accelerate the solution method in parallel.

4. The method for reducing the radiation noise of a blunt body based on active flow control according to claim 3, characterized in that: Response of the bluff body to active flow control θ The acquisition method is as follows. First, active flow control is applied to the bluff body, and different amplitude , frequency , phase parameter combinations are designed. Then, the different active flow control parameter combinations designed are respectively substituted into the formula in Step 1, and through numerical simulation, the instantaneous lift pulsation curve on the surface of the bluff body after applying the control is calculated. Among them, the phase is adjusted by turning on at different moments within a period T 0, and according to T 0 = 2 π / f 0, its corresponding period T 0 is obtained through conversion. Finally, a fast Fourier transform is performed on the instantaneous lift pulsation curve on the surface of the bluff body obtained in the previous step to obtain the amplitude, frequency, and response phase θ of the lift pulsation of the bluff body.

5. The method for reducing the radiation noise of a blunt body based on active flow control according to claim 4, characterized in that: The principle for selecting the amplitude in the control parameters is to select the minimum control amplitude on the premise of ensuring frequency locking to reduce energy consumption and the self-noise of active flow control.

6. The method for reducing the radiation noise of a blunt body based on active flow control according to claim 5, characterized in that: In step 3, the relationship between the control parameter and the total lift force on the bluff body surface Γ is as follows: Among them, is the lift amplitude in the control parameters, is the control phase in the control parameters, is the response phase in the control parameters; k represents the k th bluff body; Reducing the total lift force can reduce the radiation noise at the observation point.

7. A system for implementing the method for reducing the radiation noise of a blunt body based on active flow control according to any one of claims 1-6, characterized in that: It includes a flow field solution module and an active flow control module. The flow field solution module is used to obtain hydrodynamic information and sound pressure information at the observation point, and the active flow control module is used to output the hydrodynamic pulsation of the control flow field; The flow field solution module uses numerical simulation to calculate hydrodynamic information and sound pressure information, including the information without applying active flow control and the information with applying active flow control; The active flow control module includes jet holes provided on a plurality of bluff bodies. Two jet holes are symmetrically arranged on a single bluff body, and the fluid velocity directions in the two jet holes are opposite, that is, blowing up and sucking down or sucking down and blowing up; the phase cancellation interference between the acoustic signals on the bluff body surface is caused by the fluid dynamic pulsation output by the active flow control module, so as to achieve the purpose of reducing the noise at the observation point.

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