Method for analyzing flow-induced noise of gas film damping structure

Abstract

The application discloses a gas film damping structure flow-induced noise analysis method, comprising the following steps: step S1, establishing a gas film damping structure analysis model; step S2, establishing a gas film outer flow model; step S3, establishing a gas film inner flow model; step S4, establishing a gas film damping structure flow-induced noise model; and step S5, calculating flow-induced noise sound power: supposing that the flow-induced noise generated by the gas film damping is a point sound source, the total sound power is the superposition of the sound powers generated by the gas film inner flow field and the gas film outer flow, and the total flow-induced noise sound power of the gas film damping structure is obtained. The application can effectively analyze the intensity and influencing factors of the gas film damping structure flow-induced noise, and provides technical support for the design and application of the gas film damping.

Description

Technical Field

[0001] This invention belongs to the field of gas damping technology, specifically relating to a method for analyzing flow-induced noise in a gas film damping structure. Background Technology

[0002] Fatigue damage caused by blade vibration is a major cause of engine failure. Vibration reduction design for aero-engine blades can effectively extend their service life and improve engine safety and reliability. Film damping, with its simple structure, small added mass, and low environmental requirements, is superior to other traditional damping methods (such as friction damping, material damping, and impact damping) in that it effectively suppresses multi-mode vibrations of blades with high damping efficiency. It is primarily used for vibration reduction and suppression of aero-engine fan blades.

[0003] Film damping technology introduces gas channels on or inside the fan blades, allowing gas to flow through these channels during vibration and generating viscous and pressure damping effects. When the fan blades vibrate, the viscosity of the gas absorbs the vibration energy and converts it into heat. Simultaneously, the gas pressure balances the vibration force of the blades, thus reducing the vibration amplitude. When gas flows at high speed through the fan blades and these channels, flow-induced noise is generated. The mechanism of flow-induced noise in film damping is complex, and the noise intensity is related to multiple factors such as the size, shape, and installation location of the film damping system, and is also affected by the complex operating conditions of the blades. The flow-induced noise from film damping and the flow-induced noise from the fan blades can superimpose, significantly impacting engine performance and operation. Therefore, research on flow-induced noise in film damping is of great significance.

[0004] Current research on flow-induced noise in air-film damping structures is limited and suffers from the following shortcomings:

[0005] (1) The air film damping structure can be simplified into a thin rectangular cavity structure for research. There are many studies on cavity flow characteristics at home and abroad, but few studies on cavity flow-induced noise, and there is a lack of theoretical support.

[0006] (2) Fan blades with film damping need to fully consider the mutual influence between the fluids outside and inside the film, but most studies only consider the effect of the incoming flow on the blades, that is, they do not consider the influence of the incoming flow or the complex operating conditions of the engine on the film damping.

[0007] (3) Due to the complexity of the flow, the calculation of flow-induced noise caused by air film damping is very difficult for fan blades, making it difficult to apply in engineering.

[0008] (4) Current research mainly focuses on noise propagation, and there is a lack of effective methods for analyzing the influencing factors when noise is generated. Summary of the Invention

[0009] This invention provides a method for analyzing flow-induced noise in air-film damping structures. This invention can effectively analyze the intensity and influencing factors of flow-induced noise in air-film damping structures, providing technical support for the design and application of air-film damping.

[0010] The technical solutions to the above technical problems are as follows:

[0011] The method for analyzing flow-induced noise in air-film damped structures includes the following steps:

[0012] Step S1, establish the air film damping structure analysis model: based on the structural characteristics of the fan blade with air film damping, simplify the fan blade with air film damping into a cantilever plate model with air film damping, and establish the same coordinate system as the fan blade on the plate model.

[0013] Step S2, establish an external flow model for the air film: based on the operating conditions of the fan blades, determine the incoming flow velocity, incoming flow pressure, and incoming flow angle. The incoming flow pressure is defined as the air film inlet pressure.

[0014] Step S3, establish the flow model inside the air film: assume that the thickness of the air film is less than the length and width, take the average velocity in the thickness direction of the air film, and determine the velocity distribution and pressure distribution of the fluid inside the air film.

[0015] Step S4, establish the flow-induced noise model of the air film damping structure: The air film damping structure is simplified as a thin rectangular cavity structure. When the airflow passes through the cavity structure, it is assumed that the cavity structure is regarded as a nozzle, that is, the incoming flow u passing through the air film in the y direction y Assuming a uniform jet flow, calculate the noise power W generated by the airflow passing through the air film. y ;

[0016] Let u be the incoming flow that passes through the film air in the x-direction. x Considering the flow field as being affected by the edge plate, calculate the noise power W generated by the airflow sweeping across the membrane inlet in the x-direction. x ;

[0017] Assuming the thickness h of the air film is less than the length 2l and the width 2d of the air film, and ignoring the flow-induced noise generated by the flow in the z direction passing over the air film inlet, the sound power W0 of the flow-induced noise in the air film is obtained according to the velocity and pressure distribution equation of the fluid in the air film in step S3.

[0018] Step S5, calculate the flow-induced noise power: Assuming the flow-induced noise generated by the air-film damping is a point source, the total sound power is the superposition of the sound power generated by the flow field inside the air film and the incoming flow outside the air film. The total flow-induced noise power W of the air-film damping structure is:

[0019]

[0020] Compared with existing analysis methods, the flow-induced noise analysis method for air-film damped structures provided by this invention has the following advantages:

[0021] (1) The complex airflow inside and outside the air film damping structure has been reasonably simplified, and the flow-induced noise generated by the air film damping structure under any incoming flow can be analyzed.

[0022] (2) By introducing energy analysis, the noise of the flow field inside the air film can be obtained, and the magnitude and variation law of the flow-induced noise inside the air film can be directly analyzed.

[0023] (3) The provided calculation formula can obtain the variation law of flow-induced noise under different working conditions and is related to the parameters of the air film damping structure. It can be used to guide the design of air film damping; it can also be used to quickly determine whether the designed air film damping structure meets the specifications and requirements under different conditions. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required in the embodiments will be briefly introduced below.

[0025] Figure 1 The flowchart shows the flow-induced noise analysis method for air-film damping structures provided by this invention.

[0026] Figure 2 This is a schematic diagram of the structure of a fan blade with air film damping to which this invention applies.

[0027] Figure 3a This is a three-dimensional structural diagram of the flat plate with air film damping to which this invention applies.

[0028] Figure 3b These are schematic diagrams of the front and top views of the flat plate with air film damping to which this invention applies.

[0029] Figure 4a and Figure 4b The figure shows the calculation results of the flow-induced noise in different directions (x and y) obtained by the method of the present invention.

[0030] Figure 5 The influence of air film thickness on flow-induced noise is obtained from the flow-induced noise analysis method of the air film damping structure provided by this invention.

[0031] The labels in the attached diagram are: 1. Fan blade, 2. Fan vibration-absorbing plate, 3. Fan cavity containing air film, 4. Fan air film, 5. Cantilever plate, 6. Vibration-absorbing plate, 7. Cavity containing air film, 8. Air film, 9. Fixed end of fan blade, 10. Free end of fan blade, 11. Support end of cantilever plate, 12. Free end of cantilever plate, 13. Air film outlet, 14. Air film inlet. Detailed Implementation

[0032] The flow-induced noise analysis method for air-film damping structures provided by the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The described embodiments are only some embodiments, not all embodiments. The present invention can also be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0033] like Figure 2 As shown, the wind turbine blade with air film damping applicable to this invention includes a fan blade 1, a fan vibration-absorbing thin plate 2 covering the blade surface, a fan cavity 3 containing an air film, and a fan air film 4. When the fan blade 1 vibrates, the fan vibration-absorbing thin plate 2 absorbs the vibration of the fan blade 1 and, together with the fan blade 1, compresses the gas flow within the fan air film 4 to dissipate vibration energy, thereby generating a damping effect. During vibration, the gas within the fan air film 4 flows through the fan cavity 3 containing the air film, simultaneously generating viscous damping and pressure damping effects. Furthermore, the gas within the fan air film 4 flows in and out of the fan cavity 3 containing the air film under vibration compression, generating a pumping effect. The gas within the fan air film 4 generates flow-induced noise when it moves; when the fan blade 1 operates, the incoming flow passes over the blade surface at a certain speed and angle, and together with the gas within the fan air film 4 flows through the fan cavity 3 containing the air film, generating flow-induced noise. Because the mechanism of flow-induced noise generated by air film damping is relatively complex, calculating the flow-induced noise of air film damping presents many difficulties.

[0034] like Figure 1 As shown, the flow-induced noise analysis method for air-film damping structures provided by the present invention includes the following steps performed in sequence:

[0035] Step S1: Establish an analytical model for the air-film damping structure. For example... Figure 2 As shown in Figure 3, when studying the vibration characteristics of the fan blade structure, the fan blade with air film damping is simplified into a cantilevered plate model with air film damping. The free end 12 of the cantilevered plate corresponds to the free end 10 of the fan blade, while the supporting end 11 of the cantilevered plate corresponds to the fixed end 9 of the fan blade. The air film damping plate structure includes a cantilevered plate 5, a vibration-absorbing thin plate 6 covering the surface of the plate, a cavity containing an air film 7, and an air film 8. According to... Figure 2 The structural features of the fan blade with film damping shown are illustrated in Figure 3. A coordinate system identical to that of the fan blade is established on the cantilever plate model. While ensuring the dynamic similarity between the fan blade and the cantilever plate, the same structural parameters are retained, including the same weight and dimensions, and the same film damping structure. The length direction of the cantilever plate 5 is defined as the x-direction, the width direction as the y-direction, and the thickness direction as the z-direction. Specifically, the cantilever plate 5 has a length of 2L, a width of 2d, and a thickness of H; the film damping membrane 8 has a length of 2l, a thickness of h, and a width identical to that of the cantilever plate 5.

[0036] Step S2: Establish an extracellular flow model. For example... Figure 2 As shown in Figure 3, the incoming flow velocity, incoming flow pressure, and incoming flow angle are determined based on the operating conditions of the fan blades. Based on the incoming flow angle, the incoming flow velocity is decomposed in the three directions of the coordinate system into the incoming flow that passes over the film inlet 14 and the incoming flow that passes through the film inlet 14; the incoming flow pressure is defined as the pressure at the film inlet 14.

[0037] The incoming flow velocity, U, is decomposed in the three coordinate directions into an incoming flow u that sweeps past the film inlet 14 in the x-direction. x The incoming flow u passing through the air film 8 in the y direction y and the incoming flow u passing over the film inlet 14 in the z direction z .

[0038] The pressure at the air film inlet 14 is the incoming flow pressure P0, and the airflow flows out from the air film outlet 13.

[0039] Step S3: Establish the flow model within the air film. As shown in Figure 3, the vibration-absorbing thin plate 6 vibrates along with the cantilever plate 5, jointly compressing the gas movement within the air film 8. Assuming that the thickness h of the air film 8 is much smaller than its length 2l and width 2d, and the average velocity in the z-direction of the air film 8 is taken, the velocity distribution equation of the fluid within the air film 8 is:

[0040]

[0041] Among them, V y (x,y,t) represents the velocity of the fluid inside the air film, D0 represents the maximum relative displacement of the vibration-absorbing thin plate 6, ω represents the vibration frequency of the cantilever plate 5, t represents time, 2l represents the length of the air film, h represents the thickness of the air film, and x refers to the position in the x-direction.

[0042] The pressure distribution equation within the air film 8 is as follows:

[0043]

[0044] Where P(y) is the fluid pressure inside the gas film, γ is the fluid specific heat ratio, ρ0 is the fluid density, P0 is the gas film inlet pressure, and r n Let q be the characteristic value of the vibration mode of the cantilever plate 5. n Let y be the wave number in the y direction, κ be the complex viscosity coefficient of the gas, K be the correlation parameter, and d be the gas film width.

[0045] The complex viscosity coefficient of the gas is:

[0046] κ 2 =-jωρ0 / μ

[0047] Where j represents complex analysis and μ represents the fluid viscosity coefficient.

[0048] The associated parameters of the gas are:

[0049]

[0050] Step S4: Establish the flow-induced noise model of the air-film damping structure. As shown in Figure 3, the air-film damping structure can be simplified as a thin rectangular cavity structure. When the airflow passes through the cavity 7 containing the air film, assuming that the cavity 7 containing the air film is regarded as a nozzle, that is, the incoming flow u passing through the air film 8 in the y direction... y For a uniform jet, the noise power W generated by the airflow passing through the air film 8 is... y for:

[0051]

[0052] Where K1 is a constant, taken as K1 = 1.2 × 10 -4 ρ0 is the fluid density, u y Let h be the incoming flow through the air film in the y direction, h be the thickness of the air film, 2l be the length of the air film, and c0 be the local speed of sound.

[0053] Assume the incoming flow u in the x-direction passes over the film gas inlet 14 x Considering the flow field as being affected by the edge plate, the noise power W generated by the airflow sweeping across the film inlet 14 in the x direction is... x for:

[0054]

[0055] Where K2 is a constant, taken as K2 = 1.4 × 10 -6 ρ0 is the fluid density, u x Let 2l be the inflow passing through the film opening in the x direction, c0 be the film length, and c0 be the local sound speed.

[0056] Assuming the thickness h of the air film 8 is less than the length 2l and the width 2d, the flow-induced noise generated by the incoming flow in the z direction passing over the air film inlet 14 is ignored.

[0057] Based on the velocity and pressure distribution equations of the fluid within the air film 8 in step S3, the flow-induced noise power within the air film 8 is obtained as follows:

[0058]

[0059] Step S5: Calculate the flow-induced noise power and analyze and evaluate the influencing factors. When assessing the noise level, it is assumed that the distance between the noise receiver and the sound source is very far, far exceeding the characteristic scale of the air-film damping structure. In comparison, the influence of the air-film damping structure's dimensions is negligible. Therefore, it is assumed that the flow-induced noise generated by the air-film damping is a point source, and the total sound power is the superposition of the sound power generated by the internal flow field and the external flow within the air-film damping structure. The total flow-induced noise power of the air-film damping structure is obtained as follows:

[0060] W = W0 + W x +Wy .

[0061] Figure 4- Figure 5 Figures 4(a) and 4(b) show the calculation results of the flow-induced noise analysis method for the air-film damping structure provided by this invention. As can be seen from Figures 4(a) and 4(b), the method provided by this invention can effectively calculate the flow-induced noise from different directions. Figure 5 It can be seen that the total flow-induced noise of the air-film damping structure first decreases and then increases with the increase of the air-film thickness. This is because when the thickness is small, the total flow-induced noise is mainly controlled by the noise inside the air-film, and has an approximately fourth-power inverse relationship with the air-film thickness; when the thickness is large, the total flow-induced noise is mainly controlled by the noise outside the air-film, and has an approximately direct relationship with the air-film thickness. Therefore, there exists an air-film thickness with the minimum flow-induced noise. The method provided by this invention can also obtain the influence law of air-film structure parameters on flow-induced noise, and can provide technical support for the structural design and application of air-film damping; in addition, since the method provided by this invention does not involve complex flow calculations, its computational efficiency is much higher than that of numerical simulation methods.

[0062] The flow-induced noise analysis method for air-film damped structures provided by this invention can be used for, in addition to, Figure 2 The fan blades with air film damping and the flat plate structure with air film damping shown in Figure 3 can also be used to calculate the flow-induced noise of similar thin rectangular cavity structures.

Claims

1. A method for analyzing flow-induced noise in a film damping structure, characterized in that: Includes the following steps: Step S1, establish the air film damping structure analysis model: based on the structural characteristics of the fan blade with air film damping, simplify the fan blade with air film damping into a cantilever plate model with air film damping, and establish the same coordinate system as the fan blade on the plate model. Step S2, establish an external flow model for the air film: based on the operating conditions of the fan blades, determine the incoming flow velocity, incoming flow pressure, and incoming flow angle. The incoming flow pressure is defined as the air film inlet pressure. Step S3, establish the flow model inside the air film: assume that the thickness of the air film is less than the length and width, take the average velocity in the thickness direction of the air film, and determine the velocity distribution of the fluid inside the air film and the pressure distribution equation of the fluid inside the air film. Step S4, establish the flow-induced noise model of the air-film damping structure: The air-film damping structure is simplified as a thin rectangular cavity structure. When the airflow passes through the cavity structure, it is assumed that the cavity structure is regarded as a nozzle, that is, in Direction of incoming flow through the air film Assuming a uniform jet flow, calculate the noise power generated by the airflow passing through the air film. ; set up The direction of the incoming flow passing over the air film opening Considering the flow field as being affected by the edge plate, calculate The noise power generated by the airflow passing through the membrane inlet ; Let the air film thickness be... Less than the length of the air film and air film width ,neglect The flow-induced noise generated by the incoming flow passing over the inlet of the air film is calculated using the velocity and pressure distribution equations of the fluid within the air film in step S3. The sound power of the flow-induced noise in the air film is then obtained. ; Step S5, calculate the flow-induced noise power: Assuming the flow-induced noise generated by the air-film damping is a point source, the total sound power is the superposition of the sound power generated by the flow field inside the air film and the incoming flow outside the air film, thus obtaining the total flow-induced noise power of the air-film damping structure. for: ； The sound power of flow-induced noise generated by the air film flow field The formula for calculation is: ； in, The vibration frequency of the cantilever plate is... This represents the maximum relative displacement of the vibration-absorbing thin plate. For air film thickness, Specific heat ratio of the fluid For fluid density, For the air film inlet pressure, These are the characteristic values ​​of the vibration modes of the cantilever plate. For associated parameters, It is the complex viscosity coefficient of the gas. for Wave number in direction, The length of the air film. It refers to Direction and position.

2. The method for analyzing flow-induced noise in a film damping structure according to claim 1, characterized in that, In step S2, based on the incoming flow angle, the incoming flow velocity is decomposed in the three directions of the coordinate system into the incoming flow that passes over the air film inlet and the incoming flow that passes through the air film.

3. The method for analyzing flow-induced noise in an air-film damping structure according to claim 2, characterized in that, The flow passing through the film gas is considered a uniform jet, and the cavity containing the film gas is considered a rectangular nozzle.

4. The method for analyzing flow-induced noise in a film damping structure according to claim 1, characterized in that, The velocity distribution equation for the fluid within the gas film is as follows: ； in, The velocity of the fluid within the gas film. For time; The distribution equation of the fluid pressure within the gas film is as follows: ； in, This represents the fluid pressure within the air film.

5. The method for analyzing flow-induced noise in a film damping structure according to claim 1, characterized in that, Noise power generated by airflow passing through the air film The formula for calculation is: ； in, It is a constant. In order to be in The direction of the incoming flow through the air film, The speed of sound in the local area.

6. The method for analyzing flow-induced noise in an air-film damping structure according to claim 1, characterized in that, calculate The noise power generated by the airflow passing through the membrane inlet for: ； in, It is a constant. for The direction of the incoming flow sweeps past the membrane opening. The speed of sound in the local area.

7. The method for analyzing flow-induced noise in an air-film damping structure according to claim 1, characterized in that, The complex viscosity coefficient of the gas The formula for calculation is: ； Where j is a complex number, is the fluid viscosity coefficient.

8. The method for analyzing flow-induced noise in an air-film damping structure according to claim 1, characterized in that, The formula for calculating the correlation parameter is: 。

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