A Calculation Method for Aerodynamic Noise of Helicopter Rotors in Hovering State

Abstract

The present invention belongs to the technical field of helicopter rotor aerodynamic noise analysis and control, and discloses a method for calculating the aerodynamic noise of a helicopter rotor in a hovering state. For the working state of the blade, the blade deformation amount is calculated; according to the blade deformation amount, a three-dimensional structural grid around the deformed blade is drawn; according to the three-dimensional structural grid around the deformed blade and the flow field input parameters, the blade surface load data is calculated; according to the noise calculation input parameters, the blade surface load data and the blade body-fitted grid, the rotor noise sound field is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of helicopter rotor aerodynamic noise analysis and control, and particularly relates to a method for calculating the aerodynamic noise of a helicopter rotor in a hover state. Background Art

[0002] As one of the most important noise sources of a helicopter, rotor aerodynamic noise has received the most attention. Accurate prediction of rotor noise is a prerequisite for understanding the characteristics of rotor noise and designing a low-noise rotor. Therefore, the research on rotor noise prediction methods has important academic and engineering significance. Currently, the computational models for rotor noise prediction are generally divided into two categories. One is to use advanced CFD methods in combination with the FW-H equation for calculation; the other is to use engineering models to calculate rotor loads and combine them with the FW-H equation to calculate noise. These computational models based on the input of blade geometric shapes can determine the characteristics of rotor noise at the design stage.

[0003] For a helicopter in flight, its blades will undergo significant elastic deformations, including bending and torsion. In current studies considering blade deformation, load calculations including flexible blade dynamics and aerodynamics are used to enable acoustic codes to analyze most of the noise effects caused by blade deformation, such as the studies in References [1] and [2]. However, these studies do not consider the elastic deformation of the blade surface grid in noise calculation. This is equivalent to inaccurate input of the blade geometric shape in the computational model, which will in turn lead to inaccurate noise prediction. Load noise is not only related to the load, but also to the source position and the time derivative of the source position. Precise load calculation is not sufficient to correct these errors in source position and motion. Furthermore, the noise in the rotor plane is mainly thickness noise, and the thickness noise strongly depends on the position, velocity, and acceleration of the blade surface. These quantities need to be recalculated based on the elastic deformation of the blade.

[0004] References:

[0005] [1]Aoyama T, Yang C, Kondo N. Comparison of noise reduction effect between afc and conventional ibc by moving overlapped grid method[C] / / 12th AIAA / CEAS Aeroacoustics Conference, May 8-10, Cambridge, Britain, 2006.

[0006] [2] Kondo N, Aoyama T, Yang C. Numerical analysis of active flap for noise reduction using moving overlapped grid method[C] / / 61st Forum American Helicopter Society, June 1 - 3, Texas, U.S.A 2005. Summary of the Invention

[0007] This method comprehensively considers the problems existing in the background technology. Based on considering the elastic deformation of the blade, a method for calculating the aerodynamic noise of a helicopter rotor in hover state is established. The influence of the blade elastic deformation is considered in both the blade body - fitted grid and the calculation of the rotor unsteady load, making the calculation result of the rotor aerodynamic noise more accurate. The present invention provides the following solutions:

[0008] A method for calculating the aerodynamic noise of a helicopter rotor in hover state, the method comprising:

[0009] In the first step, for the working state of the blade, calculate the blade deformation amount;

[0010] In the second step, according to the blade deformation amount, draw a three - dimensional structured grid around the deformed blade.

[0011] In the third step, calculate the blade surface load data according to the three - dimensional structured grid around the deformed blade and the flow field input parameters;

[0012] In the fourth step, solve the rotor noise sound field according to the noise calculation input parameters, the blade surface load data and the blade body - fitted grid.

[0013] Further, in the first step, the blade deformation amount is obtained by performing blade aerodynamic / dynamic calculations on the elastic blade model through a comprehensive analysis software for rotor aircraft.

[0014] Further, the blade deformation amount includes: the torsional angle deformation amount and the displacement deformation amount at the 1 / 4 chord length position along the spanwise distribution.

[0015] Further, the displacement deformation amount at the 1 / 4 chord length position along the spanwise distribution includes the displacement deformation amount of the 1 / 4 chord length position along the flapping direction of the blade and the displacement deformation amount along the lead - lag direction of the blade.

[0016] Further, in the second step, it further includes generating a two-dimensional airfoil circumferential grid of the blade and generating the 1 / 4 chord length position points, chord lengths, and twist angles distributed along the span of the reference blade; the reference blade is the blade before deformation. The twist angle distributed along the span of the reference blade is corrected according to the twist angle deformation amount; the 1 / 4 chord length position points distributed along the span of the reference blade are corrected according to the displacement deformation amount of the 1 / 4 chord length position in the blade flapping direction along the span; the 1 / 4 chord length position points distributed along the span of the reference blade are corrected according to the displacement deformation amount of the 1 / 4 chord length position in the blade pitching direction along the span. According to the chord length of the reference blade, the corrected blade twist angle, and the distribution law of the corrected 1 / 4 chord length position of the blade along the span of the deformed blade, the coordinate transformation is performed on the two-dimensional airfoil circumferential grid at each span position, and finally a three-dimensional structural grid around the deformed blade is generated; the three-dimensional structural grid around the deformed blade is the grid outside the geometric surface of the blade.

[0017] Further, in the third step, the input parameters of the flow field include: rotor flight speed, rotor disk angle of attack, number of blades, blade radius, tip Mach number, blade rotation direction, and blade control amount.

[0018] Further, in the fourth step, the body-fitted grid of the blade is extracted from the three-dimensional structural grid around the deformed blade, and the body-fitted grid of the blade describes the geometric shape of the blade surface.

[0019] Further, the input parameters for noise calculation include: rotor flight speed, number of calculation discretization points for one rotation of the rotor, maximum harmonic order during noise spectrum analysis, rotor shaft inclination angle, number of blades, blade radius, blade chord length, tip Mach number, blade rotation direction, and blade control amount.

[0020] Advantages of the present invention: The present invention improves the background technology, can accurately depict the grid information after the elastic deformation of the blade, and provides a more accurate method for calculating the aerodynamic noise of the rotor in the hovering state considering the elastic deformation of the blade. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the two-dimensional airfoil circumferential grid of the blade;

[0022] Figure 2 It is the three-dimensional structural grid around the deformed blade;

[0023] Figure 3 It is a comparison diagram of the body-fitted grid of the reference blade and the body-fitted grid of the deformed blade;

[0024] Figure 4 It is a comparison of the total noise radiation characteristics considering blade deformation and ignoring blade deformation;

[0025] Figure 5It is the difference in total noise between considering blade deformation and ignoring blade deformation. Detailed implementation manner

[0026] The following further elaborates in detail on the method for calculating the aerodynamic noise of a helicopter rotor in the hover state involved in the present invention with reference to the accompanying drawings.

[0027] (1) For the blade working state, calculate the blade deformation amount.

[0028] (2) According to the blade deformation amount, draw a three-dimensional structural grid around the deformed blade.

[0029] (3) Calculate the blade surface load data according to the three-dimensional structural grid around the deformed blade and the flow field input parameters.

[0030] (4) Solve the rotor noise sound field according to the noise calculation input parameters, the blade surface load data, and the blade body-fitted grid.

[0031] The specific steps are as follows:

[0032] In the first step, for the blade working state, perform blade aerodynamic / dynamic modeling calculations on the elastic blade model through rotorcraft comprehensive analysis software such as CAMRAD II.

[0033] In the second step, process and analyze the calculation results to obtain the blade twist angle deformation amount and the displacement deformation amount at the 1 / 4 chord length position along the spanwise distribution. Among them, the displacement deformation amount at the 1 / 4 chord length position along the spanwise distribution includes the displacement deformation amount of the 1 / 4 chord length position along the blade flapping direction and the displacement deformation amount along the blade lead-lag direction.

[0034] In the third step, generate a two-dimensional airfoil surrounding grid for the blade, as Figure 1 shown; generate the points, chord lengths, and twist angles at the 1 / 4 chord length position along the spanwise distribution of the reference blade; the reference blade is the blade before deformation.

[0035] In the fourth step, correct the twist angle along the spanwise distribution of the reference blade according to the twist angle deformation amount; correct the points at the 1 / 4 chord length position along the spanwise distribution of the reference blade according to the displacement deformation amount of the 1 / 4 chord length position along the blade flapping direction; correct the points at the 1 / 4 chord length position along the spanwise distribution of the reference blade according to the displacement deformation amount of the 1 / 4 chord length position along the blade lead-lag direction.

[0036] In the fifth step, according to the chord length of the reference blade, the corrected blade twist angle, and the distribution law of the corrected 1 / 4 chord length position of the blade along the spanwise direction of the deformed blade, perform coordinate transformation on the two-dimensional airfoil surrounding grid at each spanwise position respectively, and finally generate a three-dimensional structural grid around the deformed blade, as Figure 2As shown; the three-dimensional structured grid around the deformed blade is the grid outside the geometric surface of the blade.

[0037] The sixth step is to calculate the blade surface load data based on the three-dimensional structured grid around the deformed blade and the flow field input parameters. Among them, the flow field input parameters include: rotor flight speed, rotor disk angle of attack, number of blades, blade radius, tip Mach number, blade rotation direction, and blade control amount.

[0038] The seventh step is to extract the body-fitted grid of the deformed blade from the three-dimensional structured grid around the deformed blade. The comparison between the body-fitted grid of the reference blade and the body-fitted grid of the deformed blade is as Figure 3 shown.

[0039] The eighth step is to solve the rotor noise sound field based on the noise calculation input parameters, blade surface load data, and blade body-fitted grid. Among them, the noise calculation input parameters include: rotor flight speed, number of calculation discretization points for one revolution time of the rotor, maximum harmonic order during noise spectrum analysis, rotor shaft inclination angle, number of blades, blade radius, blade chord length, tip Mach number, blade rotation direction, and blade control amount.

[0040] Figure 4 is the comparison of the total noise radiation characteristics considering blade deformation (the method of the present invention) and ignoring blade deformation. Figure 5 is the difference between the total noise calculated by the method of the present invention and the total noise when ignoring blade deformation.

[0041] As described above, only the specific embodiments of the present invention are given, and the present invention is described in detail. The parts not elaborated are conventional technologies. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for calculating the aerodynamic noise of a helicopter rotor in a hovering state, characterized in that: The method includes: In the first step, for the operating state of the blade, calculate the blade deformation amount; In the second step, according to the deformation amount of the blade, draw a three-dimensional structural grid around the deformed blade; generate a two-dimensional airfoil surrounding grid of the blade and generate points at the 1 / 4 chord length position, chord length, and twist angle distributed along the span of the reference blade; the reference blade is the blade before deformation; correct the twist angle distributed along the span of the reference blade according to the twist angle deformation amount; correct the points at the 1 / 4 chord length position distributed along the span of the reference blade according to the displacement deformation amount of the 1 / 4 chord length position in the flap direction of the blade; correct the points at the 1 / 4 chord length position distributed along the span of the reference blade according to the displacement deformation amount of the 1 / 4 chord length position in the lead-lag direction of the blade; according to the chord length of the reference blade, the corrected blade twist angle, and the distribution law of the corrected 1 / 4 chord length position of the blade along the span of the deformed blade, perform coordinate transformation on the two-dimensional airfoil surrounding grid at each span position respectively, and finally generate a three-dimensional structural grid around the deformed blade; In the third step, calculate the blade surface load data according to the three-dimensional structural grid around the deformed blade and the flow field input parameters; In the fourth step, solve the rotor noise sound field according to the noise calculation input parameters, the blade surface load data, and the blade body-fitted grid.

2. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 1, characterized in that: In the first step, the blade deformation amount is obtained by performing blade aerodynamic / dynamic calculations on the elastic blade model through a rotorcraft comprehensive analysis software.

3. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 2, characterized in that: In the first step, the blade deformation amount includes: the twist angle deformation amount and the displacement deformation amount at the 1 / 4 chord length position distributed along the span.

4. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 3, characterized in that: The displacement deformation amount at the 1 / 4 chord length position distributed along the span includes the displacement deformation amount of the 1 / 4 chord length position in the flap direction of the blade and the displacement deformation amount in the lead-lag direction of the blade.

5. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 4, characterized in that: In the third step, the flow field input parameters include: the rotor flight speed, the rotor disk angle of attack, the number of blade, the blade radius, the tip Mach number, the blade rotation direction, and the blade control amount.

6. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 5, characterized in that: In the fourth step, the blade body-fitted grid is extracted according to the three-dimensional structural grid around the deformed blade, and the blade body-fitted grid describes the geometric shape of the blade surface.

7. The method for calculating the aerodynamic noise of a helicopter rotor in a hovering state according to claim 6, characterized in that: The noise calculation input parameters include: the rotor flight speed, the number of calculation discretization points for one rotation time of the rotor, the maximum harmonic order during noise spectrum analysis, the rotor shaft inclination angle, the number of blade, the blade radius, the blade chord length, the tip Mach number, the blade rotation direction, and the blade control amount.

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