A method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft

Abstract

The present invention belongs to the field of fluid calculation, and specifically relates to a method for calculating the roll damping moment coefficient of a low-speed rotating aircraft. First, a three-dimensional model of the aircraft and a fluid domain of the aircraft are created, and a mesh model of the fluid domain is divided. The calculation conditions of the fluid domain are set, and the roll moment coefficient m of the aircraft under the specified conditions is calculated. x Calculate, write user-defined function UDF function, set the parameters of rolling motion, and finally compile and call the aircraft rolling motion function through fluent software to calculate the aircraft rolling damping moment coefficient C lp Calculation can effectively calculate the rolling damping moment coefficient of the aircraft under given conditions and improve calculation efficiency.

Description

Technical Field

[0001] The invention belongs to the field of fluid calculation, and in particular relates to a method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft. Background Art

[0002] For low-speed rotating aircraft, the roll damping moment coefficient is an important aerodynamic parameter. When the aircraft rotates around its longitudinal axis, a roll damping moment will be generated, which always prevents the aircraft from rotating around its longitudinal axis. When analyzing the aircraft's rotation speed, the roll damping moment is an indispensable factor, so it is necessary to obtain the roll damping moment coefficient.

[0003] At present, there are two main methods for obtaining the roll damping moment coefficient in engineering applications: one is to conduct wind tunnel tests on aircraft, and the other is to obtain it through numerical simulation calculations based on CFD (Computational Fluid Dynamics). To obtain the roll damping moment coefficient of an aircraft through wind tunnel tests, it is necessary to place the aerodynamic model of the aircraft in a wind tunnel, blow air and measure force on it to obtain the aerodynamic parameters of the aircraft. When the aircraft is blown in a rolling state, the roll damping moment coefficient will be obtained. This test method is costly and has a complicated test process, which is not conducive to being widely used in analyzing the speed characteristics of low-speed rotating aircraft; the roll damping moment coefficient of an aircraft is obtained through numerical calculation based on CFD computational fluid dynamics. This method has a low test cost and a relatively simple implementation process. By modeling the aircraft, the aerodynamic parameters of the roll damping moment coefficient of the aircraft can be obtained based on numerical calculations, which can be widely used in analyzing the speed characteristics of low-speed rotating aircraft. Summary of the invention

[0004] In order to solve the problem in the background technology, the present invention discloses a method for calculating the roll damping moment coefficient of a low-speed rotating aircraft, which effectively calculates the roll damping moment coefficient of the aircraft under given conditions and improves the calculation efficiency.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0006] A method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft comprises the following steps:

[0007] The first step is to carry out 3D modeling of the aircraft;

[0008] The second step is to create the fluid domain of the aircraft;

[0009] The third step is to divide the fluid domain grid model;

[0010] Step 4: Set the fluid domain calculation conditions;

[0011] The fifth step is to calculate the static rolling moment coefficient m of the aircraft under specified conditions. x0 calculate;

[0012] Step 6: Write a user-defined function (UDF). In the case of fixed-axis rotation, the forced motion equation is γ(t)=γ0+Asin(wt), where γ is the roll angle, γ0 is the initial roll angle, A is the motion amplitude, and w is the angular velocity. The derivative of the above motion equation with respect to time is: This is the rolling motion function of the aircraft;

[0013] Step 7: Compile and call the aircraft roll motion function in step 6 through the fluid calculation software to calculate the aircraft roll damping moment coefficient C lp calculate.

[0014] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft comprises the following steps: first, performing three-dimensional modeling of the aircraft, wherein the aircraft rotates at a low speed around its longitudinal axis, and the rotation speed is less than 30 r / s.

[0015] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft, the second step, creating the aircraft fluid domain includes setting the fluid domain to be a sphere, and the radius of the sphere is equal to 20 times the length of the aircraft.

[0016] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft, the third step, dividing the fluid domain grid model includes using an unstructured grid and setting the grid model boundary layer to 20 layers.

[0017] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft, the fourth step, setting the fluid domain calculation conditions includes setting the solver to a density basis, setting the turbulence model to a k-epsilon model, and setting the fluid domain material properties to an ideal atmosphere model.

[0018] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft, the fifth step, performs the static rolling moment coefficient m of the aircraft under specified conditions x0 Calculation, the specified conditions are aircraft speed <3Ma, angle of attack <30°, and sideslip angle <30°.

[0019] The method for calculating the rolling damping moment coefficient of the low-speed rotating aircraft, step 7, performing the rolling damping moment coefficient C of the aircraft lp Calculations, including

[0020] Dynamic rolling moment coefficient:

[0021] In the formula,

[0022] m x represents the dynamic rolling moment coefficient;

[0023] m x0 represents the static rolling moment coefficient;

[0024] C lp represents the rolling damping moment coefficient;

[0025] w x Indicates the rolling angular velocity of the aircraft;

[0026] D represents the reference length of the aircraft, usually referring to the diameter of the aircraft;

[0027] V represents the flight speed of the aircraft;

[0028] When the aircraft is rolling on a fixed axis, the equation of motion is:

[0029] γ(t)=γ0+Asin(wt)

[0030] Among them, γ is the roll angle, γ0 is the initial roll angle, A is the motion amplitude, and w is the motion angular velocity;

[0031] Differentiate the equation of motion with respect to time:

[0032] When γ=γ0,

[0033] At the same time, the rolling angular velocity of the aircraft

[0034] set up Where D is the diameter of the aircraft, V is the flight speed, and w is the angular velocity of motion.

[0035] When n=0,2,4,...,

[0036] m x+ Indicates the peak value of the dynamic rolling moment coefficient, which changes in a cosine curve;

[0037] When n=1,3,5,...,

[0038] m x- Indicates the trough value of the dynamic rolling moment coefficient, and the dynamic rolling moment coefficient changes in a cosine curve;

[0039] Therefore,

[0040] The rolling damping moment coefficient of the aircraft can be solved according to the above formula.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The method for calculating the roll damping moment coefficient of a low-speed rotating aircraft disclosed in the present invention has a clear principle and a relatively simple implementation process. By constraining the size of the fluid domain, the number of grids can be effectively controlled to reduce the amount of calculation. By setting the calculation conditions of the fluid domain, the calculation efficiency can be effectively improved, which is conducive to the rapid convergence of the solution process, so as to effectively reduce the complexity of solving the roll damping moment coefficient, effectively calculate the roll damping moment coefficient of the aircraft under given conditions, and improve the calculation efficiency.

[0043] The method for calculating the roll damping moment coefficient of a low-speed rotating aircraft disclosed in the present invention has a relatively wide range of applications and can basically include typical speeds, angles of attack and sideslip angles of the aircraft, and can meet the needs of solving the roll damping moment coefficient under different calculation conditions of the aircraft. DETAILED DESCRIPTION

[0044] The present invention provides a method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft, and the calculation steps are as follows:

[0045] 1. Complete the 3D modeling of the aircraft;

[0046] 2. Create the fluid domain of the aircraft and set the fluid domain to be a sphere with a radius equal to 20 times the length of the aircraft;

[0047] 3. Divide the fluid domain grid model, use unstructured grid, and set the grid model boundary layer to 20 layers;

[0048] 4. Set the calculation conditions of the fluid domain, set the solver to density basis, set the turbulence model to k-epsilon model, and set the material properties of the fluid domain to ideal atmosphere model;

[0049] 5. The static rolling moment coefficient m of the aircraft under specified conditions x0 Calculation: The applicable conditions of the method of the present invention are that the aircraft speed is less than 3Ma, the angle of attack is less than 30°, and the sideslip angle is less than 30°. The static rolling moment coefficient calculation under the specified conditions is completed and the "xxx.cas and xxx.dat" files are output;

[0050] 6. Write a user-defined function (UDF) to set the parameters of the rolling motion, including the motion amplitude A, the angular velocity w, the rolling motion time step t, and the motion equation

[0051] After the function is written, the "xxx.c" file is output, and the file is compiled by the fluid calculation software. After compilation, the "Roll:libudf" file will be generated;

[0052] 7. Calculate the aircraft rolling damping moment coefficient C lp The detailed calculation method is as follows:

[0053] 1) Read the "xxx.cas and xxx.dat" files. After reading, set the solver to transient calculation;

[0054] 2) Call the "Roll:libudf" file generated after compilation;

[0055] 3) Set the fluid domain to "Mesh Motion" and select the motion form to "Roll:li budf";

[0056] 4) Set all surfaces of the aircraft as moving surfaces, i.e. “Moving Wall”;

[0057] 5) Set the fluid calculation time step t. When calculating the dynamic rolling moment coefficient, the relevant parameters include the reference length of the aircraft, the flight speed V, the angular velocity w, and the axial center of mass position of the aircraft. The reference length of the aircraft usually refers to the diameter D of the aircraft. Set the dimensionless coefficient

[0058] The k value can be set to a constant greater than zero, and its value does not affect the calculation result. When the present invention is used for calculation verification, k=0.1 is set, and the angular velocity of the aircraft is Aircraft rolling motion time period When performing fluid calculation, it is assumed that each rolling motion cycle is iterated for n steps. When performing calculation verification in the present invention, n=100 is set, and the rolling motion time step is At the same time, the rolling motion amplitude A is set. The value of A can be arbitrarily set to a constant greater than zero, and its value does not affect the calculation result. When calculating and verifying the present invention, A is set to 0.25°;

[0059] 6) Setting the calculation cycle, calculating m cycles, where m is a non-zero positive integer. When calculating and verifying the method of the present invention, m=5 is set;

[0060] 7) Set the total number of calculation steps = n*m, set n = 100, m is a non-zero positive integer, start the calculation, and after completing each step of the calculation, output a dynamic rolling moment coefficient m x Value, the dynamic rolling moment coefficient will change in a cosine curve in each cycle;

[0061] 8) According to the output dynamic rolling moment coefficient m x The peak and trough values ​​of the rolling damping moment coefficient are solved by the following formula:

[0062]

[0063] m x+ Indicates the peak value of the dynamic rolling moment coefficient, which changes in a cosine curve;

[0064] m x- Indicates the trough value of the dynamic rolling moment coefficient, and the dynamic rolling moment coefficient changes in a cosine curve;

[0065] 9) A C can be obtained in each cycle lp The rolling damping moment coefficient C of the aircraft under the specified conditions is obtained by averaging the m periodic values. lp .

[0066] The above description is only a preferred practical embodiment of the present invention and does not limit the invention in any form. Any technician familiar with the profession may use the technical solution disclosed above to change or modify it into an equivalent implementation example with equivalent changes. However, any simple modification, equivalent change and modification made to the above implementation example based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft, characterized in that: The steps include: The first step is to carry out 3D modeling of the aircraft; The second step is to create the fluid domain of the aircraft; The third step is to divide the fluid domain grid model; Step 4: Set the fluid domain calculation conditions; The fifth step is to calculate the static rolling moment coefficient m of the aircraft under specified conditions. x0 calculate; Step 6: Write a user-defined function (UDF). In the case of fixed-axis rotation, the forced motion equation is γ(t)=γ0+Asin(wt), where γ is the roll angle, γ0 is the initial roll angle, A is the motion amplitude, and w is the angular velocity. The derivative of the above motion equation with respect to time is: is the rolling motion function of the aircraft; Step 7: Use the fluent software to compile and call the aircraft roll motion function in step 6, and combine it with the dynamic roll moment coefficient formula to calculate the aircraft roll damping moment coefficient C. lp calculate, include, Dynamic rolling moment coefficient: In the formula, w x Indicates the rolling angular velocity of the aircraft; When γ=γ0, At the same time, the rolling angular velocity of the aircraft set up Where D is the diameter of the aircraft, V is the flight speed, and w is the angular velocity of motion; but 2. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: The first step is to perform three-dimensional modeling of the aircraft, wherein the aircraft rotates around its longitudinal axis at a low speed of less than 30 r / s.

3. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: The second step is to create the fluid domain of the aircraft, which includes setting the fluid domain to a sphere with a radius equal to 20 times the length of the aircraft.

4. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: The third step is to divide the fluid domain grid model, including using unstructured grids and setting the grid model boundary layer to 20 layers.

5. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: The fourth step is to set the calculation conditions of the fluid domain, including setting the solver to density basis, setting the turbulence model to the k-epsilon model, and setting the fluid domain material properties to the ideal atmosphere model.

6. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: The fifth step is to calculate the static rolling moment coefficient m of the aircraft under specified conditions. x0 Calculation, the specified conditions are aircraft speed <3Ma, angle of attack <30°, and sideslip angle <30°.

7. The method for calculating the rolling damping moment coefficient of a low-speed rotating aircraft according to claim 1, characterized in that: Step 7: Calculate the aircraft rolling damping moment coefficient C lp calculate, When n=0,2,4,..., m x+ Indicates the peak value of the dynamic rolling moment coefficient, which changes in a cosine curve; When n=1,3,5,..., m x- Indicates the trough value of the dynamic rolling moment coefficient, and the dynamic rolling moment coefficient changes in a cosine curve; Therefore, The rolling damping moment coefficient of the aircraft can be solved according to the above formula.

Images