Multi-rotor aircraft and method based on rotor support arm included angle noise reduction

Abstract

The invention provides a multi-rotor aircraft and method based on rotor support arm included angle noise reduction, the method is applied to the multi-rotor aircraft, and the method comprises the following steps: pre-establishing a noise simulation database according to sound radiation hemisphere noise data corresponding to the geometric shape, overall parameters and flight state of the multi-rotor aircraft; acquiring flight parameters of the multi-rotor aircraft in flight; extracting a group of sound radiation hemisphere noise data of different rotor support arm included angles corresponding to the flight parameters from the noise simulation database; selecting a target position for noise reduction; wherein the target position comprises a direction and a region; based on an optimization algorithm and the extracted sound radiation hemisphere noise data, obtaining an optimal rotor support arm included angle combination with the lowest noise at the target position; by adjusting the included angle of the rotor supporting arms, multiple beams of sound waves at specific positions interfere with one another, the effect of mutual counteraction is achieved, and finally noise control over the multi-rotor aircraft is achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of noise reduction of multi-rotor aircraft, and specifically relates to a multi-rotor aircraft and a method based on noise reduction of rotor arm angle. Background Art

[0002] Compared with fixed-wing aircraft, multi-rotor aircraft can achieve fixed-point hovering, vertical take-off and landing, and have the characteristics of high maneuverability; compared with conventional helicopters, it has the characteristics of small size, simple structure, simple control and low cost.

[0003] The above characteristics have led to the rapid development of multi-rotor aircraft, and the demand for industrial and commercial applications has increased year by year. The high noise limits the environmental performance of civil multi-rotor aircraft, so it is very important to reduce the noise level of multi-rotor aircraft. Summary of the invention

[0004] The purpose of the present invention is: taking into account that each rotor of a multi-rotor has a similar noise waveform and amplitude, but a significant difference in phase, by adjusting the angle of the rotor arm, multiple beams of sound waves at specific positions interfere with each other, achieving the effect of mutual cancellation, and ultimately realizing noise control of the multi-rotor aircraft.

[0005] In a first aspect, the present application provides a multi-rotor aircraft based on rotor arm angle noise reduction, the multi-rotor aircraft comprising: a rotor arm having a rotor; An actuator connected to the rotor support arm; An aircraft control system connected to the actuator; Wherein, the aircraft control system is used to drive the actuator to extend and retract, and the actuator drives the rotor arm to move until an optimal rotor arm angle combination is reached.

[0006] Preferably, the multi-rotor aircraft further comprises: a power supply for supplying power to the aircraft control system; Joint bearing, the actuator is connected to the rotor arm through the joint bearing.

[0007] In a second aspect, the present application further provides a method for noise reduction based on the rotor arm angle, the method being applied to the multi-rotor aircraft as described above, the method comprising: A noise simulation database is established in advance based on the acoustic radiation hemispherical noise data corresponding to the multi-rotor aircraft's geometric shape, overall parameters and flight status; Get the flight parameters of the multi-rotor aircraft in flight; Extracting a set of acoustic radiation hemispherical noise data of different rotor arm angles corresponding to the flight parameters from the noise simulation database; Selecting a target position for noise reduction; wherein the target position includes a direction and an area; Based on the optimization algorithm and the extracted acoustic radiation hemispherical noise data, the optimal rotor arm angle combination with the lowest noise at the target position is obtained.

[0008] Preferably, the noise simulation database is pre-established based on the acoustic radiation hemispherical noise data corresponding to the geometric shape, overall parameters and flight state of the multi-rotor aircraft, including: According to the geometric shape and overall parameters of the multi-rotor aircraft, a calculation model of the aerodynamic noise of the multi-rotor aircraft is established; Using the aerodynamic noise calculation model, aerodynamic noise simulation calculation is carried out to obtain the acoustic radiation hemispherical noise data corresponding to different flight states and different arm angles; The acoustic radiation hemispherical noise data is merged into a noise simulation database to form the noise simulation database, and is stored in an aircraft control system.

[0009] Preferably, the overall parameters include the number of rotors, the number of rotor blades, the relative position between the rotors, the direction of rotation of the rotors, the Mach number of the rotor tip when hovering, and the take-off weight.

[0010] Preferably, the aerodynamic noise calculation model includes three parts: rotor blade grid generation, rotor blade surface aerodynamic load data calculation and aircraft aerodynamic noise calculation.

[0011] Preferably, the arm angle is the angle between the rotor arm and the horizontal line of the flight direction.

[0012] Preferably, the method further comprises: If the noise simulation database does not have the sound radiation hemispherical noise data directly corresponding to the flight parameters, the corresponding sound radiation hemispherical data is obtained by interpolation method.

[0013] Preferably, the method further comprises: The aircraft control system drives the actuator to extend and retract according to the optimal rotor arm angle combination, and the actuator drives the rotor arm to move until the required rotor arm angle is reached.

[0014] Beneficial technical effects of this application: The present invention provides a multi-rotor aircraft noise reduction method based on arm angle control, which performs targeted noise reduction for specific target positions and has a good noise reduction effect. The present invention can be extended to aircraft with two or more rotors, and has broad application prospects. The present invention uses its own coherent sound source to reduce noise, avoids the introduction of secondary sound sources, and has little effect on the aerodynamic performance of the aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A flow chart of a noise control method for a multi-rotor aircraft provided in an embodiment of the present application; Figure 2 A schematic diagram of a numerical noise simulation database provided in an embodiment of the present application; Figure 3 A basic diagram of the quadcopter provided in the embodiment of the present application; Figure 4 A schematic diagram of the arm angle of a quadrotor aircraft in a single degree of freedom optimized state provided in an embodiment of the present application; Figure 5 A schematic diagram of the angle of the arms of a quadrotor aircraft in a dual-degree-of-freedom optimized state provided in an embodiment of the present application; Figure 6 A schematic diagram of a two-dimensional interpolation method provided in an embodiment of the present application; Figure 7 A schematic diagram of a noise reduction target area provided in an embodiment of the present application; Figure 8 The noise sound pressure level results before and after optimization provided in the embodiments of the present application. DETAILED DESCRIPTION See also Figure 1-Figure 8 , the present invention provides the following scheme: (1) For a multi-rotor aircraft that needs to implement noise control, obtain the shape and overall parameters of the multi-rotor aircraft.

[0016] (2) Conduct multi-rotor aircraft noise simulation modeling based on the multi-rotor aircraft shape and flight parameters. The aerodynamic load calculation of the multi-rotor aircraft can be performed by computational fluid dynamics (CFD) or free wake method, and the noise calculation is based on solving the FW-H equation. This step can also be replaced by the measured multi-rotor aircraft noise results.

[0017] (3) Obtain the sound pressure level data of the sound radiation ball under different flight parameter states (different flight speeds, different blade angles) and different arm angles. The angle between the rotor arm and the horizontal line of the flight direction is the angle between the rotor arm and the horizontal line of the flight direction. To avoid collision with the rotor blade tip, there is a limit on the arm angle, which is generally a minimum of 30° and a maximum of 60°.

[0018] (4) All sound pressure level data are merged into the multi-rotor aircraft noise database.

[0019] (5) For multi-rotor aircraft on a mission, flight parameter collection is completed through sensors.

[0020] (6) Process the sensor data to obtain flight speed and flight attitude data.

[0021] (7) Determine the corresponding flight speed and propeller angle according to the flight speed and flight attitude, and extract the acoustic radiation sphere data of different arm angles in the current state from the database. If there is no such data, obtain the corresponding acoustic radiation sphere data by interpolation.

[0022] (8) Determine the target noise reduction location based on the flight mission requirements. The target noise reduction location can be the flight destination or the enemy detection radar area.

[0023] (9) The rotor arm angle combination with the best noise is calculated through optimization algorithms such as proxy models. The optimization has two modes: single degree of freedom and double degree of freedom. Single degree of freedom means that the angles of the rotor arms are the same, and double degree of freedom means that the angles of the front rotor and the rear rotor arms are different.

[0024] (10) The aircraft control system drives each rotor arm to achieve the optimal angle combination.

[0025] (11) Achieve noise reduction at the target position.

[0026] In other embodiments of the present application, the present invention provides the following solutions: (1) A noise simulation database is established in advance based on the acoustic radiation hemispherical noise data corresponding to the multi-rotor aircraft's geometric shape, overall parameters, and flight status.

[0027] Specifically, according to the geometric shape and overall parameters of the multi-rotor aircraft, a multi-rotor aircraft aerodynamic noise calculation model is established, and the helicopter aerodynamic noise calculation model is used to carry out aerodynamic noise simulation calculation, and the acoustic radiation hemispherical noise data corresponding to different flight states and different arm angles are calculated, such as Figure 2 The acoustic radiation hemispherical noise data is merged into a noise simulation database and stored in an aircraft control system.

[0028] Among them, the overall parameters include the number of rotors, the number of rotor blades, the relative position between the rotors, the direction of rotor rotation, the rotor tip Mach number in hovering state, take-off weight, etc.

[0029] The flight status includes the flight speed and body attitude angle of the multirotor aircraft.

[0030] Among them, the aerodynamic noise calculation model includes three parts: rotor blade grid generation, rotor blade surface aerodynamic load data calculation and aircraft aerodynamic noise calculation.

[0031] 1) Rotor blade mesh generation: The "tiling method" is used to generate the three-dimensional structural mesh around the blade. The "tiling method" decomposes the blade into a two-dimensional airfoil and a one-dimensional beam model for separate processing. The specific generation steps are as follows: Generate a C-shaped two-dimensional structural mesh around the airfoil used by the blade and a one-dimensional mesh with the span-wise grid points of the blade; Tiling the two-dimensional mesh along the span of the blade according to the span-wise grid point distribution law. When multiple airfoils are configured, the cross-sectional mesh of the blade transition section is obtained by linear interpolation of the standard airfoil mesh at both ends of the transition section; the root and tip parts are folded to generate an O-shaped folded mesh; according to the distribution law of the blade's chord length (scaling), aerodynamic center position (translation) and torsion angle (rotation) along the span, the coordinates of the two-dimensional mesh points of each blade span are transformed, and finally the three-dimensional structural mesh around the blade is obtained.

[0032] 2) The aerodynamic load data on the rotor blade surface is calculated using the computational fluid dynamics method. Specifically, the generated rotor blade mesh is used to solve the aircraft flow field calculation using the three-dimensional unsteady Reynolds averaged NS (RANS) equation in the inertial coordinate system, and the aerodynamic load data on the rotor blade surface is calculated. The expression is as follows:

[0033] In the formula, is the conserved variable vector, and are the inviscid flux and the viscous flux respectively; is the unit volume. In the solution process, the spatial discretization format uses the MUSCL+Roe second-order inverse wind format, the time advancement uses the dual-time method and implicit LU-SGS format, and the turbulence model uses the SA-equation model. The undisturbed flow field at infinity is used as the initial condition, and the no-slip boundary condition is used as the kinematic boundary condition at the object surface.

[0034] 3) Calculation of aircraft aerodynamic noise: The rotor blade surface aerodynamic load data and the rotor blade mesh are substituted into the Farassat 1A (F 1A) formula to calculate the aircraft aerodynamic noise. Thus, the aircraft aerodynamic noise calculation model is established.

[0035] The Farassat 1A (F 1A) formula is as follows:

[0036]

[0037] Where: represents the speed of sound in an undisturbed medium, is the blade surface equation, Indicates that the variables in the brackets are all taken at the delay time; r is the distance between the source item and the observation point, l is the blade surface element load, the subscripts r and M are the projections along the propagation direction and the source surface motion Mach number direction respectively, M is the source surface motion Mach number, and dS represents the surface element of the blade surface.

[0038] The arm angle is defined as the angle between the rotor arm and the horizontal line of the flight direction, such as Figure 4 As shown, in order to avoid rotor tip collision, there are restrictions on the arm angle, generally with a minimum of 30° and a maximum of 60°.

[0039] (2) For a multi-rotor aircraft in flight, the flight parameters are measured by sensors; Among them, the flight parameters include flight speed and fuselage attitude angle.

[0040] Among them, the flight speed is measured by the speed sensor, and the fuselage attitude angle is measured by the attitude sensor.

[0041] (3) According to the flight speed and the fuselage attitude angle, a set of acoustic radiation hemispherical noise data of different arm angles corresponding to the flight speed and the fuselage attitude angle are extracted from the noise simulation database in the aircraft control system.

[0042] Preferably, if there is no sound radiation hemispherical noise data directly corresponding to the flight speed and the fuselage attitude angle in the noise simulation database, the corresponding sound radiation hemispherical data is obtained by an interpolation method.

[0043] Specifically, when only one of the parameters, flight speed or fuselage attitude angle, cannot determine the corresponding acoustic radiation hemispherical noise data, it is only necessary to solve the interpolation under the change of this parameter, find the acoustic radiation hemispherical noise data closest to this parameter, and use the first-order linear interpolation method through the two acoustic radiation hemispherical noise data to calculate the required acoustic radiation hemispherical noise data. However, in general, the two parameters cannot correspond, and the most commonly used method is two-dimensional linear interpolation. The interpolation method is as follows: Figure 6 shown.

[0044] For example, to calculate the value of function f at point P = (v, α), where v is the flight speed and α is the fuselage attitude angle. When it is known that function f is at Q 11 =(v1,α1),Q 12 =(v1,α2),Q 21 =(v2,α1),Q 22 = (v2, α2) The values ​​of the four positions are first linearly interpolated in the v direction to obtain:

[0045] Then perform linear interpolation in the α direction and obtain:

[0046] In summary, the final calculation result of two-dimensional linear interpolation is:

[0047] (8) Select the target location for noise reduction, such as Figure 7 As shown, the corresponding location can be the flight destination of the aircraft or a noise-sensitive area, such as a school or a nursing home; The target location can be a direction or an area.

[0048] (9) The rotor arm angle combination with the lowest noise at the target position is calculated through the optimization method based on the proxy model.

[0049] This includes determining the design variables (arm angle), the range of each design variable (angle range 30°~60°), and the optimization target (lowest noise at the target position).

[0050] The specific process is as follows: 1) Initial sample point generation: The initial sample points are selected from a set of different arm angles.

[0051] 2) Calculation of the response value of the initial sample point: The sound pressure level at the target position is extracted from a set of sound radiation hemispherical noise data with different arm angles.

[0052] 3) Establish the proxy model of the objective function and constraint function based on the sample points and response values. The Kriging model can be used in the modeling process.

[0053] 4) Perform sub-optimization on the proxy model according to the point-adding criteria. For each point-adding criterion, perform the following operations: a) For the Pareto multi-objective optimization problem, the multi-objective genetic algorithm NAGA-II is used for optimization to obtain the Pareto solution set on the surrogate model; b) For single-objective or multi-objective optimization problems with weighted coefficients, a hybrid optimization method is used to solve the sub-optimization problems.

[0054] 5) Check whether the optimal point obtained by the sub-optimization overlaps or overlaps with the original sample set. If there is overlap, eliminate the optimal point; otherwise, use it as a sample point to be verified.

[0055] 6) Calculation of the corresponding value of the sample point to be verified: Through the interpolation method, the sound pressure level of the target position corresponding to the sample point to be verified is extracted from a set of sound radiation hemispherical noise data with different arm angles.

[0056] 7) Add the data of the sample points to be verified to the sample set.

[0057] 8) Save the results: a) For single-objective or linearly weighted multi-objective optimization problems, save the optimal value of all current sample points, which is the optimal arm angle combination; b) For the Pareto multi-objective optimization problem, all sample points are non-dominatedly sorted, where all individuals in the first rank (Rank 1) are the current true Pareto solution set, that is, the optimal arm angle combination.

[0058] Since all target position noise calculations in the entire optimization process are directly extracted or interpolated from the noise simulation database, the optimization process can be completed instantly, and the optimal arm angle combination can be calculated in real time according to the flight status.

[0059] Among them, there are two modes of optimization: single degree of freedom and double degree of freedom. Single degree of freedom means that the angles of each rotor arm are the same, such as Figure 4 As shown in Figure 1, double degrees of freedom refer to the different angles of the front rotor and rear rotor arms, such as Figure 5 shown.

[0060] (10) The aircraft control system drives the two actuators to extend and retract according to the calculated optimal arm angle combination, and drives the rotor arm to move through the ball head rod end joint bearing to achieve the required arm angle, as shown in the figure.

[0061] (11) When the target position of noise reduction is a direction, the results before and after noise optimization by controlling the arm angle are as follows: Figure 8 shown.

Claims

1. A multi-rotor aircraft based on rotor arm angle noise reduction, characterized in that: The multi-rotor aircraft comprises: a rotor arm having a rotor; An actuator connected to the rotor support arm; An aircraft control system connected to the actuator; Wherein, the aircraft control system is used to drive the actuator to extend and retract, and the actuator drives the rotor arm to move until an optimal rotor arm angle combination is reached.

2. The multi-rotor aircraft according to claim 1, characterized in that: The multi-rotor aircraft also includes: a power supply for supplying power to the aircraft control system; Joint bearing, the actuator is connected to the rotor arm through the joint bearing.

3. A method for noise reduction based on rotor arm angle, characterized in that: The method is applied to the multi-rotor aircraft according to any one of claims 1 to 2, and the method comprises: A noise simulation database is established in advance based on the acoustic radiation hemispherical noise data corresponding to the multi-rotor aircraft's geometric shape, overall parameters and flight status; Get the flight parameters of the multi-rotor aircraft in flight; Extracting a set of acoustic radiation hemispherical noise data of different rotor arm angles corresponding to the flight parameters from the noise simulation database; Selecting a target position for noise reduction; wherein the target position includes a direction and an area; Based on the optimization algorithm and the extracted acoustic radiation hemispherical noise data, the optimal rotor arm angle combination with the lowest noise at the target position is obtained.

4. The method according to claim 3, characterized in that The noise simulation database is pre-established based on the acoustic radiation hemispherical noise data corresponding to the geometric shape, overall parameters and flight state of the multi-rotor aircraft, including: According to the geometric shape and overall parameters of the multi-rotor aircraft, a calculation model of the aerodynamic noise of the multi-rotor aircraft is established; Using the aerodynamic noise calculation model, aerodynamic noise simulation calculation is carried out to obtain the acoustic radiation hemispherical noise data corresponding to different flight states and different arm angles; The acoustic radiation hemispherical noise data is merged into a noise simulation database to form the noise simulation database, and is stored in an aircraft control system.

5. The method according to claim 4, characterized in that The overall parameters include the number of rotors, the number of rotor blades, the relative position between the rotors, the direction of rotation of the rotors, the Mach number of the rotor tip when hovering, and the take-off weight.

6. The method according to claim 4, characterized in that The aerodynamic noise calculation model includes three parts: rotor blade grid generation, rotor blade surface aerodynamic load data calculation and aircraft aerodynamic noise calculation.

7. The method according to claim 3, characterized in that The arm angle is the angle between the rotor arm and the horizontal line of the flight direction.

8. The method according to claim 3, characterized in that The method further comprises: If the noise simulation database does not have the sound radiation hemispherical noise data directly corresponding to the flight parameters, the corresponding sound radiation hemispherical data is obtained by interpolation method.

9. The method according to claim 3, characterized in that: The method further comprises: The aircraft control system drives the actuator to extend and retract according to the optimal rotor arm angle combination, and the actuator drives the rotor arm to move until the required rotor arm angle is reached.

Images