Double-compact prediction method for helicopter rotor thickness noise

Abstract

The present invention discloses a dual-compact prediction method for helicopter rotor thickness noise in the field of helicopter power design. The method comprises the following steps: dividing a helicopter rotor blade into a plurality of blade units along a span direction; cutting each blade unit into two parts along a thickness direction at a position of a maximum thickness section; applying a uniform pressure load to the surfaces of the two parts respectively; integrating the uniform pressure loads on the surfaces of the two parts respectively, and obtaining two load vectors with equal amplitudes and opposite directions for each blade unit, both of which point to and are perpendicular to the maximum thickness section of the blade unit; applying a load vector perpendicular to the blade tip and blade root cross sections to each of the two blade units located at the blade tip and blade root respectively, and calculating the load noise generated by all the load vectors, i.e., the thickness noise generated by the helicopter rotor blade; while ensuring prediction accuracy, the method effectively improves efficiency and has applicability and prediction accuracy for different blade tips.

Description

Technical Field

[0001] The present invention relates to the field of helicopter power design, in particular to a method for predicting helicopter rotor thickness noise, so as to improve the acoustic evaluation efficiency of the helicopter in the early design stage. Background Art

[0002] Helicopter aerodynamic noise is crucial for both civil and military aircraft. As civil aviation noise airworthiness regulations become increasingly stringent, helicopter noise has become as important as performance, safety, reliability, and manufacturing. Helicopter aerodynamic noise can be divided into two main categories: discrete-frequency noise and broadband noise. Discrete-frequency noise primarily includes thickness noise, load noise, blade-vortex interference noise, and high-speed impulse noise; broadband noise primarily includes turbulent induction noise, blade wake interference noise, and blade self-noise.

[0003] Thickness noise is a significant component of helicopter aerodynamic noise. It is generated by the volume of air displaced by the movement of helicopter rotor blades, and its magnitude is primarily determined by blade geometry and helicopter operating conditions. Within the rotor surface, thickness noise dominates, and its amplitude is primarily determined by the rotor tip Mach number. Because forward-canted blades have the highest tip Mach number, the maximum thickness noise occurs directly in front of the helicopter within the rotor surface.

[0004] Currently, the compact load noise prediction method is relatively mature. It approximates the blade as a series of units at different radial positions, but does not consider the distribution of the load along the chord length. Compared with traditional prediction methods based on distributed blade loads, it can greatly improve the calculation speed without significantly losing accuracy. Compared with the compact load noise prediction method, the prediction of traditional rotor thickness noise still requires the use of geometric information of the entire blade surface, so the thickness noise calculation time is much longer than the compact load noise calculation time. Therefore, how to improve the thickness noise prediction speed and significantly enhance the efficiency of evaluating the acoustic characteristics of multiple design options in the early stages of helicopter blade design has become a difficult problem in the field of helicopter design. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of long calculation time and slow prediction speed in the existing helicopter rotor thickness noise calculation and propose a double-compact prediction method for helicopter rotor thickness noise, which requires less geometric information and improves the calculation speed without significantly losing the prediction accuracy.

[0006] To achieve the above objectives, the dual-compact prediction method for helicopter rotor thickness noise of the present invention adopts the following technical solutions:

[0007] Divide the helicopter rotor blade into a plurality of blade units along the span direction, and cut each blade unit into two parts along the thickness direction at the position of the maximum thickness section;

[0008] Apply uniform pressure load to the surfaces of the two parts respectively;

[0009] The uniformly distributed pressure loads on the surfaces of the two parts are integrated respectively, and two load vectors with equal amplitudes and opposite directions are obtained for each blade element. Both load vectors point to and are perpendicular to the maximum thickness section of the blade element.

[0010] The load noise generated by all load vectors is calculated, which is the thickness noise generated by the helicopter rotor blades.

[0011] Furthermore, the two blade units located at the tip and the root are divided into two parts at the positions of the maximum thickness sections of the tip cross section and the root cross section, respectively. Each part is applied with a tip load vector perpendicular to the tip cross section and a root load vector perpendicular to the root cross section. All the load vectors include the tip load vector and the root load vector.

[0012] Furthermore, the pressure amplitude of the uniformly distributed pressure load is ρ0 is the atmospheric density and c0 is the speed of sound in the atmosphere.

[0013] Furthermore, the amplitude of the tip load vector is equal to Multiplied by the area of the blade tip cross section, the magnitude of the blade root load vector is equal to Multiply by the area of the blade root cross section.

[0014] Furthermore, the thickness noise at any observation point of the blade is matched with the thickness noise standard result to obtain the action positions of the two load vectors of the two parts.

[0015] Along the blade chord direction, the position where the quotient of the coordinate values of the two load vectors and the blade chord length is located is the action position of the two load vectors.

[0016] The first load vector acts at position X f / c=0.133, the action position of the second load vector is x f / c=0.867, which are the coordinate values of the first and second load vectors in the blade chord direction, and c is the blade chord length.

[0017] Along the thickness direction of the blade, the action positions of the two load vectors are exactly in the middle of the thickness direction.

[0018] The two blade units located at the tip and the root are divided into two parts at the position of the maximum thickness section of the tip cross section and the root cross section, respectively. Each part is applied with a tip load vector perpendicular to the tip cross section and a root load vector perpendicular to the root cross section. The tip load vector and the root load vector act on the action positions at the tip and the root respectively at the same time, and are perpendicular to the tip cross section and the root cross section respectively.

[0019] The beneficial effects of the present invention after adopting the above technical solution are:

[0020] Traditional rotor thickness noise prediction methods require geometric information of the entire blade surface, and their calculation time is significantly longer than the current compact load noise calculation time, which objectively limits the efficiency of acoustic evaluation of multiple design schemes in the early stages of design. The dual-compact prediction method proposed in the present invention has applicability and prediction accuracy for different blade tips while ensuring prediction accuracy. The calculation time is close to the current compact load noise calculation time, and the calculation speed can be increased by 25 times compared with the traditional thickness noise prediction method. This can effectively improve the efficiency of acoustic evaluation of multiple design schemes in the early stages of design. At the same time, due to the greatly shortened noise calculation time, it also makes real-time noise prediction for objects such as helicopter rotors possible. The present invention can also be applied to objects such as propellers and open rotors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] To better illustrate the purpose and advantages of the present invention, the following further describes the invention in detail with reference to the accompanying drawings and specific embodiments:

[0022] Figure 1 Schematic diagram of the pressure distribution and integrated load vector of a single blade unit:

[0023] Figure 2 Schematic diagram of the load vector of the entire blade along the span direction;

[0024] Figure 3 for Figure 2 Enlarged view of the cross section of the middle leaf root;

[0025] Figure 4 This is a comparison curve diagram of the time domain standard result of thickness noise at the observation point directly in front of the rotor within the rotor surface corresponding to the NACA 0006 airfoil and the prediction result of the prediction method of the present invention. The solid line curve in the figure represents the time domain standard result, and the dotted line curve represents the prediction result of the prediction method of the present invention;

[0026] Figure 5This is a comparison curve diagram of the thickness noise spectrum standard result at the observation point directly in front of the rotor within the rotor surface corresponding to the NACA 0006 airfoil and the prediction result of the prediction method of the present invention. The square dashed curve in the figure represents the time domain standard result, and the three square dashed curves represent the prediction result of the prediction method of the present invention;

[0027] Figure 6 This is a comparison curve diagram of the time domain standard result of thickness noise at an observation point directly in front of the rotor within a narrow blade shape and the prediction result of the prediction method of the present invention. The solid line curve in the figure represents the time domain standard result, and the dotted line curve represents the prediction result of the prediction method of the present invention;

[0028] Figure 7 This is a comparison curve diagram of the thickness noise spectrum standard result at the observation point directly in front of the rotor within the rotor surface corresponding to a narrow blade shape and the prediction result of the prediction method of the present invention. The square dashed curve in the figure represents the time domain standard result, and the three square dashed curves represent the prediction result of the prediction method of the present invention;

[0029] Figure 8 Graph comparing the standard time-domain thickness noise result at the observation point directly in front of the rotor within the rotor plane at a blade tip Mach number of 0.676 and the prediction result of the prediction method of the present invention. The solid line curve in the figure represents the standard time-domain result, and the dotted line curve represents the prediction result of the prediction method of the present invention.

[0030] Figure 9 This is a comparison curve diagram of the standard result of the thickness noise spectrum at the observation point directly in front of the rotor within the rotor surface with a blade tip Mach number of 0.676 and the prediction result of the prediction method of the present invention. The square dotted curve in the figure represents the standard result in the time domain, and the three square dotted curves represent the prediction result of the prediction method of the present invention. DETAILED DESCRIPTION

[0031] The present invention is based on Isom's thickness noise calculation idea. When the surface load of a helicopter rotor blade is a uniform pressure distribution, the load noise generated by the blade is equal to its thickness noise. Therefore, the present invention divides the blade into two parts at each radial position, and integrates the uniform pressure distribution of these two parts separately. In this way, two load lines are obtained at two different chord positions of the blade. The load noise calculated from these two load lines can reproduce the thickness noise result. Through multiple verifications, including different airfoils, different blade shapes, and different blade tip Mach numbers, the results show that the predicted noise time domain and spectrum results correspond well to the standard results. Specifically as follows:

[0032] See also Figure 1The helicopter rotor blade is divided into several blade units along the span direction, with the x direction being the blade chord direction and the y direction being the thickness direction, with the origin being on the maximum thickness section 2. For each blade unit, it is cut along the y direction at the location of the maximum thickness section 2, thus cutting each blade unit into two parts 3. A uniform pressure load 1 is applied to the surfaces of the two parts respectively. The uniform pressure amplitude of the uniform pressure load 1 is Where ρ0 is the atmospheric density and c0 is the speed of sound in the atmosphere. By integrating the uniformly distributed pressure load 1 on the two surfaces, two load vectors 4 are obtained for each blade element. These two load vectors 4 have equal magnitudes and opposite directions. Both load vectors 4 point perpendicularly to the maximum thickness section 2 of the blade element.

[0033] The positions of the optimal action points of the two load vectors 4 along the x direction are in the blade chord direction, which are the quotients of the coordinate values of the two load vectors 4 along the x direction (blade chord direction) and the blade chord length. That is, the position of the optimal action point of the first load vector 4 is x f / c, the optimal value of the quotient of the coordinate value in the x direction and the blade chord length in the present invention is: f / c=0.133. The optimal action point of the second load vector 4 is x r / c, the optimal value of the quotient of the coordinate value in the x direction and the blade chord length in the present invention is: r / c=0.867. Among them, X f and x r are the x-direction coordinate values of the two load vectors 4, and C is the chord length of the blade.

[0034] Along the thickness direction of the blade, the action positions of the two load vectors are exactly in the middle of the thickness direction.

[0035] In the two blade elements located at the tip and root, in addition to obtaining Figure 1 In addition to the two load vectors 4 shown perpendicular to the maximum thickness section 2, as shown Figure 2 and Figure 3 As shown, a tip load vector 8 perpendicular to the tip cross section 7 and a root load vector 6 perpendicular to the root cross section 5 also need to be considered.

[0036] The tip cross section 7 and the root cross section 5 are divided into two parts at the positions of the maximum thickness sections of the tip cross section 7 and the root cross section 5, respectively. A tip load vector 8 perpendicular to the tip cross section 7 and a root load vector 6 perpendicular to the root cross section 5 are applied to each part. The amplitude of the tip load vector 8 is equal to Multiplied by the area of the blade tip cross section 7, the magnitude of the blade root load vector 6 is equal to Multiply by the area of the blade root cross section 5.

[0037] For the two blade units at the tip and root, after the optimal action point positions of the two load vectors 4 of each blade unit along the x-direction are determined, the tip load vector 8 and the root load vector 6 also act on the optimal action point positions at the tip and root, respectively, and are only perpendicular to the tip cross section 7 and the root cross section 5, respectively.

[0038] Therefore, the blade is divided into several blade elements along the span direction. For each blade element, two load vectors perpendicular to the maximum thickness section are applied. These two vectors are equal in magnitude and opposite in direction, and both point to the maximum thickness section. In addition to the two load vectors perpendicular to the maximum thickness section, the blade elements at the tip and root also have load vectors directed and perpendicular to the blade section, such as Figure 2 The two load vector action position lines 9 are shown in FIG.

[0039] Based on the two load vectors 4 of each blade unit, as well as the blade root load vector 6 and the blade tip load vector 8, the load noise generated by all these load vectors is calculated using conventional methods. The calculated total load noise is the thickness noise generated by the helicopter rotor blade.

[0040] The thickness noise results at any observation point are calculated using the traditional method and the prediction method of the present invention. Figure 4 As shown, the airfoil used is NACA 0006, with a blade chord length of 0.38 meters, an operating condition of a forward flight ratio of 0.3, a corresponding forward-inclined blade tip Mach number of 0.8, and the selected observation point is located directly in front of the rotor within the rotor surface. The calculation result using the noise prediction method of the present invention is the load noise calculated based on the load vector, while the calculation result using the traditional method is considered to be the thickness noise standard result. By matching the peak-to-peak value of the thickness noise results at the observation point calculated by the traditional method and the prediction method of the present invention, the action position of the load vector in the noise prediction method of the present invention is determined. The optimal action position obtained is the quotient of the coordinate value of the two load vectors 4 along the x-direction and the blade chord length.

[0041] The noise prediction method of the present invention is verified by different examples. First, different airfoils are examined, including symmetrical airfoils with different maximum thicknesses, such as NACA 0006, NACA 0024 airfoils, asymmetric airfoils NACA 9312, wind turbine airfoils S830, and supercritical airfoils SC(2)-0714. For each airfoil, the thickness noise time domain standard result at the observation point in front of the rotor inside the rotor surface is compared with the prediction result of the noise prediction method of the present invention. The thickness noise spectrum standard result at this observation point is compared with the result of the noise prediction method of the present invention as shown in FIG. Figure 5As shown in the figure, it can be seen that for various airfoils, whether for the noise time domain results or the spectrum results, the standard results and the results of the present invention have good correspondence. Therefore, the noise prediction method of the present invention has applicability and prediction accuracy for different airfoils.

[0042] Verify the applicability of the noise prediction method of the present invention to different blade shapes. The blade shapes investigated include narrow blades with a chord length of 0.2 meters, wide blades with a chord length of 0.8 meters, blades with trimmed blade tips, and blades with swept blade tips. Figure 6 The thickness noise time domain standard results and the noise prediction method calculation results of the present invention at the observation point directly in front of the rotor in the rotor plane corresponding to only the narrow blades are shown, and Figure 7 The standard results for the thickness noise spectrum and the dual-compact prediction model calculations for the narrow blades within the rotor plane at the observation point directly in front of the rotor are shown. It can be seen that for all blade shapes, both the time-domain noise results and the spectrum results show good correspondence between the standard results and the proposed method. Therefore, the noise prediction method of the present invention has applicability and prediction accuracy for different blade shapes.

[0043] The applicability of the prediction method of the present invention to different blade tip Mach numbers was verified. The blade tip Mach numbers used were 0.676 and 0.86, and the corresponding forward flight ratios were 0.1 and 0.4, respectively. Figure 8 Only the time domain standard results of thickness noise at the observation point directly in front of the rotor in the rotor plane with a blade tip Mach number of 0.676 and the prediction results of the prediction method of the present invention are shown. Figure 9 Only the standard thickness noise spectrum results and the prediction results of the present invention's prediction method are shown for the observation point directly in front of the rotor within the rotor plane at a blade tip Mach number of 0.676. It can be seen that for each blade tip Mach number, both the noise time domain results and the spectrum results show good correspondence between the standard results and the prediction results of the present invention's prediction method. Therefore, the noise prediction method of the present invention has applicability and prediction accuracy for different blade tip Mach numbers.

[0044] Compare the difference in calculation time between the traditional method and the noise prediction method of the present invention. The helicopter used is Bell 430, and the main rotor and tail rotor are included in the noise calculation. The airfoils of the main rotor and tail rotor blades are both NACA 0012, and the shapes are both rectangular. The radius of the main rotor blade is 6.4 meters and the chord length is 0.366 meters; the radius of the tail rotor blade is 1.05 meters and the chord length is 0.244 meters. The forward flight speed of the helicopter is 51.4m / s, and the corresponding Mach number at the tip of the forward-inclined blade is 0.836. Calculate the noise results within 0 to 30 seconds at the observation point directly in front of the rotor in the rotor surface. For the main rotor blades, the traditional prediction method uses a grid of 20 in the span direction and 100 in the chord direction, while the grid used in the present invention is 20 (span direction) × 2 (chord direction). For tail rotor blades, the traditional prediction method uses a grid of 20 (spanwise) × 100 (chordwise), while the present invention uses a grid of 20 (spanwise) × 2 (chordwise). Results show that, using an Intel Core i5 processor, the computation time for the traditional method is 1266.3 seconds, while the computation time for the present invention is 50.3 seconds. The traditional method's computation time is approximately 25 times that of the present invention, demonstrating that the present invention significantly reduces computational time.

Claims

1. A double-compact prediction method for helicopter rotor thickness noise, characterized by: Divide the helicopter rotor blade into a plurality of blade units along the span direction, and cut each blade unit into two parts along the thickness direction at the position of the maximum thickness section; Apply uniform pressure load to the surfaces of the two parts respectively; The uniformly distributed pressure loads on the surfaces of the two parts are integrated respectively, and two load vectors with equal amplitudes and opposite directions are obtained for each blade element. Both load vectors point to and are perpendicular to the maximum thickness section of the blade element. The load noise generated by all load vectors is calculated, which is the thickness noise generated by the helicopter rotor blades.

2. The double-compact prediction method for helicopter rotor thickness noise according to claim 1, characterized in that: The two blade units located at the tip and the root are divided into two parts at the positions of the maximum thickness sections of the tip cross section and the root cross section, respectively. Each part is applied with a tip load vector perpendicular to the tip cross section and a root load vector perpendicular to the root cross section. All the load vectors mentioned include the tip load vector and the root load vector.

3. The double-compact prediction method for helicopter rotor thickness noise according to claim 1, characterized in that: The pressure amplitude of the uniformly distributed pressure load is ρ0 is the atmospheric density and c0 is the speed of sound in the atmosphere.

4. The double-compact prediction method for helicopter rotor thickness noise according to claim 2, characterized in that: The magnitude of the tip load vector is equal to Multiplied by the area of the blade tip cross section, the magnitude of the blade root load vector is equal to Multiply by the area of the blade root cross section, ρ0 is the atmospheric density, and c0 is the speed of sound in the atmosphere.

5. The double-compact prediction method for helicopter rotor thickness noise according to claim 1, characterized in that: The thickness noise at any observation point of the blade is matched with the thickness noise standard result to obtain the action positions of the two load vectors of the two parts.

6. The double-compact prediction method for helicopter rotor thickness noise according to claim 5, characterized in that: Along the blade chord direction, the position where the quotient of the coordinate values of the two load vectors and the blade chord length is located is the action position of the two load vectors.

7. The double-compact prediction method for helicopter rotor thickness noise according to claim 6, characterized in that: The first load vector acts at x f / c=0.133, the action position of the second load vector is x r / c=0.867,x f and x r are the coordinate values of the first and second load vectors in the blade chord direction, and c is the blade chord length.

8. The double-compact prediction method for helicopter rotor thickness noise according to claim 6, characterized in that: Along the thickness direction of the blade, the action positions of the two load vectors are exactly in the middle of the thickness direction.

9. The double-compact prediction method for helicopter rotor thickness noise according to claim 6, characterized in that: The two blade units located at the tip and the root are divided into two parts at the position of the maximum thickness section of the tip cross section and the root cross section, respectively. Each part is applied with a tip load vector perpendicular to the tip cross section and a root load vector perpendicular to the root cross section. The tip load vector and the root load vector act on the action positions at the tip and the root respectively at the same time, and are perpendicular to the tip cross section and the root cross section respectively.

Images