An aerodynamic characteristic analysis method considering the interference of rotor fuselage and tail rotor

Abstract

The application belongs to the technical field of helicopter aerodynamic design analysis, and particularly relates to an aerodynamic characteristic analysis method considering rotor fuselage tail rotor interference. The method comprises the following steps: S1, modeling the rotor, the fuselage and the tail rotor in a three-dimensional modeling software to obtain a rotor model, a fuselage model and a tail rotor model; S2, performing grid division on the rotor model, the fuselage model and the tail rotor model according to a set grid division strategy to obtain a rotor grid model, a fuselage grid model and a tail rotor grid model; the set grid division strategy comprises a grid type, a calculation domain size, a grid number, a grid distribution and a boundary layer setting; S3, setting a multi-stage relative motion coordinate system, which comprises a rotating coordinate system, a flapping coordinate system and a pitch coordinate system, defining the rotation, flapping and pitch motion of the rotor blade in the rotating coordinate system, the flapping coordinate system and the pitch coordinate system respectively to obtain a rotor blade displacement equation; and S4, simulating a rotor fuselage tail rotor interference flow field according to the rotor blade displacement equation and the rotor grid model, the fuselage grid model and the tail rotor grid model, and obtaining the aerodynamic characteristic considering the rotor fuselage tail rotor interference according to the rotor fuselage tail rotor interference flow field.

Description

Technical Field

[0001] This invention belongs to the field of helicopter aerodynamic design and analysis technology, and particularly relates to an aerodynamic characteristic analysis method that takes into account the interference of rotor fuselage and tail rotor. Background Technology

[0002] During flight, helicopters exhibit significant unsteady flow characteristics. During hovering and low-speed forward flight, the fuselage and tail rotor are almost entirely within the rotor's wake interference flow field. This interference generates impact and periodic loads on the rotor, fuselage, and tail rotor, affecting the helicopter's handling, vibration, and noise characteristics. Furthermore, the interaction between the rotor, fuselage, and tail rotor alters the rotor and tail rotor blade angles of attack, affecting the induced velocity distribution and rotor disk load distribution, leading to fluctuations in aerodynamic forces and power, thus posing challenges to helicopter aerodynamic performance analysis. Therefore, accurately simulating the rotor-fuselage-tail rotor interference flow field and analyzing the aerodynamic interference characteristics of the rotor-fuselage-tail rotor is of significant practical importance.

[0003] There are three main methods for analyzing the aerodynamic characteristics of helicopter rotor fuselage and tail rotor: theoretical methods, experimental methods, and numerical simulation methods. Theoretical methods require model simplification, often resulting in lower computational accuracy, and are unsuitable for calculating the aerodynamic characteristics of unsteady flow fields under complex flow conditions. Experimental methods are limited by model size and measurement technology, leading to longer research cycles and higher costs. Thanks to the rapid development of fluid mechanics and computing, numerical simulation methods, represented by Computational Fluid Dynamics (CFD), have been applied in helicopter aerodynamics. They are cost-effective, have short computational cycles, and offer high accuracy, handling complex shapes well and capturing details of flow field disturbances, thus finding widespread application in helicopter flow field disturbance studies.

[0004] Existing technologies are limited by the speed difference between the rotor and tail rotor and the difficulty in simulating the interference flow field. The analysis of helicopter aerodynamic interference characteristics is mostly limited to the interference flow field of the rotor and fuselage, which cannot accurately simulate the real working environment of helicopters, and the analysis of some complex interference problems is not thorough enough. Summary of the Invention

[0005] The technical solution of this invention comprehensively considers the influence of the rotor tail rotor and provides an aerodynamic characteristic analysis method involving rotor fuselage tail rotor interference, providing support for helicopter aerodynamic layout design and aerodynamic interference characteristic analysis.

[0006] To achieve the above objectives, the present invention employs the following technical solution.

[0007] An aerodynamic characteristic analysis method considering the interference of the rotor fuselage and tail rotor, the method comprising:

[0008] S1. In the 3D modeling software, the rotor, fuselage and tail rotor are modeled separately to obtain rotor model, fuselage model and tail rotor model.

[0009] S2, according to the set meshing strategy, the rotor model, fuselage model and tail rotor model are meshed to obtain rotor mesh model, fuselage mesh model and tail rotor mesh model; the set meshing strategy includes: mesh type, computational domain size, number of meshes, mesh distribution and boundary layer settings.

[0010] S3, set up a multi-level entanglement motion coordinate system, which includes: a rotation coordinate system, a flapping coordinate system, and a pitch coordinate system. Define the rotation, flapping, and pitch motions of the blades under the rotation coordinate system, the flapping coordinate system, and the pitch coordinate system respectively, and obtain the blade displacement equations.

[0011] S4. Based on the blade displacement equation, as well as the rotor grid model, fuselage grid model, and tail rotor grid model, simulate the rotor-fuselage-tail rotor interference flow field, and obtain the aerodynamic characteristics considering the rotor-fuselage-tail rotor interference based on the rotor-fuselage-tail rotor interference flow field.

[0012] Furthermore,

[0013] In S1, the fuselage model is divided into components and simplified locally without affecting the basic flow characteristics of the model. The non-airfoil sections at the root of the rotor and tail rotor are also simplified.

[0014] Furthermore,

[0015] In S2, the specific mesh generation strategy is as follows:

[0016] The mesh type is: structured mesh, unstructured mesh, or hybrid mesh;

[0017] Meshing methods include: nested moving meshes, dynamic meshes, or sliding meshes;

[0018] Computational domain size: For rotor and tail rotor, the computational domain boundary should be between 1.5 and 2 times the chord length from the rotor and tail rotor surface; for fuselage, the computational domain boundary should be between 15 and 20 times the fuselage length from the fuselage surface.

[0019] Grid distribution: The surface grid is refined on the leading edge of the rotor and tail rotor blades, the blade tip grid, and the leading edge grid of the fuselage horizontal and vertical tail. The spatial grid is refined in the rotor and tail rotor wash area.

[0020] Boundary layer settings: Set the thickness of the first layer of the blade boundary layer mesh to the blade chord length * 10. -5 Set the thickness of the first layer of the fuselage boundary layer mesh to fuselage length * 10. -5 .

[0021] Furthermore,

[0022] S3 sets up a multi-level motion coordinate system, which includes: a rotation coordinate system, a waving coordinate system, and a variable-distance coordinate system, specifically:

[0023] A rotating coordinate system is established with the rotation center of the rotor or tail rotor as the origin. The X direction of the rotating coordinate system is the incoming flow direction, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule. The rotational motion of the rotor or tail rotor is defined in the rotating coordinate system.

[0024] In the rotating coordinate system, a flapping coordinate system is established with the flapping hinge position of the rotor or tail rotor as the origin. The X direction of the flapping coordinate system points to the blade tip, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule. In the flapping coordinate system, the flapping motion of the rotor or tail rotor is defined.

[0025] In the flapping coordinate system, a variable pitch coordinate system is established with the variable pitch position of the rotor or tail rotor as the origin. The X direction of the variable pitch coordinate system points to the blade tip, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule. In the variable pitch coordinate system, the variable pitch motion of the rotor or tail rotor is defined.

[0026] Based on the rotational motion, flapping motion, and pitch-changing motion of the rotor or tail rotor in the multi-stage entanglement motion coordinate system, the blade displacement equation is obtained.

[0027] Furthermore,

[0028] In S4, the blade displacement equations are assigned to the rotor mesh model and the tail rotor mesh model to solve the interference flow field of the rotor fuselage and tail rotor.

[0029] Furthermore,

[0030] In S4, the Reynolds-averaged NS equations are chosen as the main governing equations to solve the interference flow field of the rotor fuselage and tail rotor. The Reynolds-averaged NS equations are spatially discretized using the Roe-MUSCL scheme.

[0031] The k-ωSST two-equation turbulence model or the SA turbulence model is selected as the turbulence model for the rotor fuselage and tail rotor interference flow field.

[0032] Furthermore,

[0033] In S4,

[0034] A dual-time method was used to time-step the flow field of the rotor fuselage and tail rotor. The dual-time method includes physical time and pseudo-time. The LU-SGS scheme was used to advance the flow field in the pseudo-time until the flow field completely converged.

[0035] In terms of physical time settings, the time for the rotor blades to rotate 1° is selected as the physical time during the calculation process. After the rotor flow field basically converges, the time for the tail rotor blades to rotate 1° is selected as the physical time for numerical simulation until the flow field completely converges.

[0036] Furthermore,

[0037] In S4,

[0038] The far-field boundary of the rotor fuselage and tail rotor interference flow field is set as free flow, and the surface of the rotor fuselage and tail rotor is set as a wall.

[0039] This invention relates to a method for analyzing aerodynamic characteristics under the interference of a rotor fuselage and tail rotor. Based on CFD numerical simulation, it involves demand analysis and implementation schemes, computational model processing, computational mesh generation, definition of rotor fuselage and tail rotor motion, and numerical solution settings. By comprehensively considering the influence of the rotor fuselage and tail rotor, it accurately simulates and analyzes the aerodynamic interference characteristics of a helicopter rotor fuselage and tail rotor under real-world operating conditions, providing support for helicopter aerodynamic layout design and aerodynamic interference characteristic analysis. Compared to traditional theoretical and experimental methods, this method offers a more intuitive and thorough analysis of complex interference problems, significantly saving time and human resource costs. Attached Figure Description

[0040] Figure 1 A schematic diagram of the rotor blade grid provided in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the tail rotor blade grid provided in an embodiment of the present invention;

[0042] Figure 3 A schematic diagram of the interference flow field of the tail rotor of a rotorcraft provided in an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram of the isolated tail rotor thrust frequency provided in an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram of the tail rotor thrust frequency under the aerodynamic interference flow field of the tail rotor of a rotor fuselage provided in an embodiment of the present invention;

[0045] Figure 6 This is a schematic diagram of the aerodynamic interference flow field of the tail rotor of a rotorcraft and the frequency of the lateral force of the vertical tail, provided in an embodiment of the present invention.

[0046] Figure 7 This is a schematic diagram of the vertical force frequency of the right horizontal stabilizer in the aerodynamic interference flow field of the tail rotor of a rotorcraft provided in an embodiment of the present invention.

[0047] Figure 8 A schematic diagram of the vertical force frequency of the left horizontal stabilizer in the aerodynamic interference flow field of the tail rotor of a rotorcraft provided in an embodiment of the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0049] In helicopter development, CFD methods are typically used to determine the aerodynamic characteristics of the rotor, tail rotor, and fuselage separately, rarely considering the combined effects of the rotor, fuselage, and tail rotor. This approach fails to accurately simulate and analyze the aerodynamic interference characteristics of the rotor, fuselage, and tail rotor under real-world helicopter operating conditions, and its analysis of some complex interference problems is insufficient. This invention develops a comprehensive aerodynamic characteristic analysis method that considers rotor, fuselage, and tail rotor interference through numerical simulation scheme formulation, computational model processing, computational mesh generation, rotor-fuselage-tail rotor motion definition, and numerical solution settings. This provides support for helicopter aerodynamic layout design and aerodynamic interference characteristic analysis.

[0050] The main steps of this invention are as follows:

[0051] 1. Numerical simulation scheme development

[0052] Based on the purpose of numerical simulation, object analysis is performed to confirm state consistency, and a numerical simulation plan is formulated, including calculation state, model processing requirements, and selection of calculation methods.

[0053] a) By conducting numerical simulations of aerodynamic interference of the rotor fuselage and tail rotor, parameters such as aerodynamic forces of the fuselage and components (short wings, horizontal stabilizer, vertical stabilizer, etc.), thrust and torque of the rotor / tail rotor blades in the interference flow field are obtained.

[0054] b) Select the calculation state based on the purpose of numerical simulation, including hovering, level flight, side flight, and oblique descent.

[0055] c) Due to the complex spatial motions (blade rotation motion and periodic pitch, flapping, and oscillation motions) and strong interference of the rotor and tail rotor, we choose to carry out numerical simulations using motion nested mesh, moving mesh, or sliding mesh and unsteady calculation methods.

[0056] 2. Computational Model Processing

[0057] Based on the object and purpose of the numerical simulation, the shape of the numerical simulation is adapted, including the processing of the fuselage model, rotor model and tail rotor model, etc., and the geometric dimensions of the calculation model are determined according to the calculation conditions.

[0058] Geometric model processing was performed in 3D modeling software. Following the principle of not affecting the basic flow characteristics of the model, the fuselage model underwent component division and local simplification, with simplification of the non-airfoil sections at the root of the rotor and tail rotor.

[0059] 3. Computational mesh generation

[0060] Based on the numerical simulation model, the mesh generation strategy is determined, including mesh type, computational domain size, number of meshes, mesh distribution, boundary layer scheme, etc., see [link to relevant documentation]. Figures 1-2 .

[0061] a) For numerical simulation of interference in the rotor-fuselage-tail rotor combination, structured mesh, unstructured mesh, or hybrid mesh are selected for the rotor, fuselage, and tail rotor;

[0062] b) The boundary of the computational domain should be far enough away from the rotor fuselage and tail rotor model to ensure stable and accurate calculations;

[0063] c) The meshing method can be either a nested motion mesh, a moving mesh, or a sliding mesh. The nested motion mesh method generates a body-fitted mesh for complex moving parts (rotor, tail rotor blades) separately. Through motion nesting, it accurately describes the multidimensional motion of the blades. During flow field calculation, the relative position between the blade mesh and the background mesh is constantly changing. It is necessary to ensure that there are enough layers in the overlapping area of ​​the background mesh and the nested mesh to complete the identification of hole boundary elements and the search of contributing elements to achieve interpolation iteration in the nested region. When generating rotor and tail rotor blade meshes using moving and sliding meshes, the background mesh in the moving region should be densified to ensure accurate simulation of blade flow details.

[0064] d) The leading edge of the rotor and tail rotor blades, the blade tip grid, and the leading edge grid of the fuselage horizontal and vertical tail have good shape preservation, and the spatial grid is refined in the rotor and tail rotor wash area.

[0065] e) Set the thickness, number of layers, and growth rate of the first layer of the blade boundary layer mesh. The thickness of the first layer of the blade boundary layer mesh should fully consider the influence of boundary layer viscosity, i.e., satisfy the viscosity factor y. + ≈1.

[0066]

[0067] 4. Definition of Rotorcraft Fuselage and Tail Rotor Motion

[0068] Based on the purpose of numerical simulation of the rotor fuselage and tail rotor, motion balancing is carried out for helicopters with different weight centers and different engine speeds. The results are used as motion inputs for the rotor and tail rotor blades.

[0069] During hovering, the main focus is on motion parameters such as fuselage attitude, rotor / tail rotor blade speed, collective pitch, and cone angle.

[0070] In forward flight, the main focus is on motion parameters such as forward speed, fuselage attitude, rotor / tail rotor blade speed, and cyclic motion (including pitch change, flapping, and oscillation).

[0071] Displacement equations for rotor / tail rotor blades:

[0072] S(ψ)=a0+a1·cos(ψ)+b1·sin(ψ)+a2·cos(2ψ)

[0073] +b2·sin(2ψ)+a3·cos(3ψ)+b3·sin(3ψ)+…

[0074]

[0075] Where S(ψ) represents the blade displacement (flapping, pitching, oscillation motion) corresponding to the azimuth angle ψ, the rotor speed is ω, and the number of blades is n.

[0076] By setting up multi-level coupled motion coordinate systems (including rotation, flapping, and pitch coordinate systems), and defining blade displacement equations in the corresponding coordinate systems, complex motion coupling of each blade is achieved. Motion control of the rotor and tail rotor is realized by providing blade mesh motion constraints.

[0077] 5. Numerical Solution Settings

[0078] To better capture the unique flow details in the aerodynamic disturbance flow field of the rotor fuselage and tail rotor, and to comprehensively consider the influence of compressible and incompressible flow in the rotor, the spatial motion of the rotor tail rotor is accurately described. The flow field control equations, spatial discretization methods, time propagation schemes, turbulence models, and boundary conditions are defined.

[0079] a) The Reynolds-averaged Navier-Stokes equations were chosen as the main control equations for the numerical simulation of the combined disturbance of the rotor, fuselage and tail rotor in the flow field.

[0080] b) Spatial discretization of the Reynolds-averaged Navier-Stokes equations was performed using the finite volume method, employing the Roe-MUSCL scheme.

[0081] c) Due to the unsteady characteristics of the flow field caused by the rotor fuselage and tail rotor, a dual-time method (including physical time and pseudo-time) is adopted for time stepping. The flow control equations are advanced in pseudo-time within each physical time step, transforming the unsteady problem into a process of solving a steady problem. The LU-SGS scheme is used in pseudo-time for advancement until complete convergence.

[0082] In terms of physical time settings, the time for the blade to rotate 1° is usually selected. Since the tail rotor speed is usually much greater than the rotor speed, in order to accelerate the convergence of the flow field, the time for the rotor blade to rotate 1° is selected as the physical time in the early calculation process. After the rotor flow field has basically converged, the time for the tail rotor blade to rotate 1° is selected as the physical time for numerical simulation until the combined disturbance flow field is completely converged.

[0083] Accelerate flow field convergence and improve computational efficiency by directly setting pseudo-time steps.

[0084] The CFL number can be set smaller in the early stages to stabilize the solution, and then increased after the flow field stabilizes to ensure solution efficiency.

[0085] d) To better capture the flow within the blade boundary layer, the k-ωSST two-equation turbulence model or the SA turbulence model can be selected. The k-ωSST two-equation turbulence model is a neutral turbulence model combining k-ω and k-ε. The k-ω turbulence model is used for the near-wall flow field to better predict the turbulent viscosity coefficient, increasing simulation accuracy. The k-ε model is less sensitive to incoming flow conditions and is more suitable for the boundary layer and free shear layer, improving solution efficiency.

[0086] e) Boundary conditions can be set according to the purpose of CFD numerical simulation, selecting far-field boundary conditions or surface boundary conditions.

[0087] Complete the simulation of the interference flow field of the rotor-fuselage-tail rotor combination based on the above steps, see... Figure 3 The aerodynamic interference characteristics of the rotor, fuselage, and tail rotor in the disturbed flow field were obtained. The isolated tail rotor thrust frequency is shown in [reference needed]. Figure 4 The tail rotor thrust frequency under the aerodynamic interference flow field of the rotor fuselage tail rotor is shown in the figure. Figure 5 The frequency of the aerodynamic interference flow field of the rotor fuselage and tail rotor, and the lateral force of the vertical tail are shown in the figure. Figure 6 The frequency of the vertical force on the right horizontal stabilizer in the aerodynamic interference flow field of the rotor fuselage and tail rotor is shown in the figure. Figure 7 The frequency of the vertical force on the left horizontal stabilizer is shown in the aerodynamic interference flow field of the rotor fuselage and tail rotor. Figure 8 .

[0088] This invention relates to a method for analyzing aerodynamic characteristics under the interference of a rotor fuselage and tail rotor. Based on CFD numerical simulation, it involves demand analysis and implementation schemes, computational model processing, computational mesh generation, definition of rotor fuselage and tail rotor motion, and numerical solution settings. By comprehensively considering the influence of the rotor fuselage and tail rotor, it accurately simulates and analyzes the aerodynamic interference characteristics of a helicopter rotor fuselage and tail rotor under real-world operating conditions, providing support for helicopter aerodynamic layout design and aerodynamic interference characteristic analysis. Compared to traditional theoretical and experimental methods, this method offers a more intuitive and thorough analysis of complex interference problems, significantly saving time and human resource costs.

Claims

1. A method of aerodynamic characteristic analysis considering interference of a tail rotor with a fuselage of a rotorcraft, characterized by, The method comprises: S1, modeling the rotor, fuselage and tail rotor respectively in a three-dimensional modeling software to obtain a rotor model, a fuselage model and a tail rotor model; S2, performing mesh division on the rotor model, the fuselage model and the tail rotor model according to a set mesh division strategy to obtain a rotor mesh model, a fuselage mesh model and a tail rotor mesh model; the set mesh division strategy comprises: mesh type, calculation domain size, mesh quantity, mesh distribution and boundary layer setting; in S2, the set mesh division strategy is specifically: the mesh type is: structural mesh, unstructured mesh or hybrid mesh; the mesh method is: moving embedded mesh, dynamic mesh or sliding mesh; the calculation domain size: for the rotor and the tail rotor, the calculation domain boundary should be between 1.5 to 2 times the chord length away from the rotor and tail rotor surface; for the fuselage, the calculation domain boundary should be between 15 to 20 times the fuselage length away from the fuselage surface; the mesh distribution: the surface mesh of the rotor and tail rotor blade leading edge, blade tip and the fuselage vertical tail leading edge is encrypted, and the space mesh in the rotor and tail rotor wash area is encrypted; Boundary layer setting: set the first layer thickness of the blade boundary layer grid to be 10 times the blade chord length -5 , set the first layer thickness of the fuselage boundary layer grid to be 10 times the fuselage length -5 ; S3, setting a multi-level related motion coordinate system, the multi-level related motion coordinate system comprises: a rotation coordinate system, a flapping coordinate system and a pitch coordinate system, the rotation, flapping and pitch motions of the blade are defined in the rotation coordinate system, the flapping coordinate system and the pitch coordinate system respectively to obtain a blade displacement equation; S4, simulating the rotor, fuselage and tail rotor interference flow field according to the blade displacement equation and the rotor mesh model, the fuselage mesh model and the tail rotor mesh model, and obtaining the aerodynamic characteristics considering the rotor, fuselage and tail rotor interference according to the rotor, fuselage and tail rotor interference flow field.

2. The aerodynamic characteristic analysis method considering the rotor, fuselage and tail rotor interference according to claim 1, characterized in that: in S1, the fuselage model is divided into parts and simplified locally without affecting the basic flow characteristics of the model, and the non-airfoil section of the rotor and tail rotor root is simplified.

3. The method of claim 1, wherein S3, setting a multi-level related motion coordinate system, the multi-level related motion coordinate system comprises: a rotation coordinate system, a flapping coordinate system and a pitch coordinate system, and specifically: a rotation coordinate system is established with the rotation center of the rotor or tail rotor as the origin, the X direction of the rotation coordinate system is the flow direction, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule; in the rotation coordinate system, the rotation motion of the rotor or tail rotor is defined; a flapping coordinate system is established with the flapping hinge position of the rotor or tail rotor as the origin in the rotation coordinate system, the X direction of the flapping coordinate system points to the blade tip, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule; in the flapping coordinate system, the flapping motion of the rotor or tail rotor is defined; a pitch coordinate system is established with the pitch position of the rotor or tail rotor as the origin in the flapping coordinate system, the X direction of the pitch coordinate system points to the blade tip, the Z direction is vertically upward, and the Y direction is determined by the right-hand rule; in the pitch coordinate system, the pitch motion of the rotor or tail rotor is defined; the blade displacement equation is obtained according to the rotation motion, flapping motion and pitch motion of the rotor or tail rotor in the multi-level related motion coordinate system.

4. The method of claim 3, wherein, In S4, the blade displacement equation is given to the rotor grid model and the tail rotor grid model, and the rotor fuselage tail rotor interference flow field is solved.

5. The method of claim 4, wherein, In S4, the Reynolds averaged N-S equation is selected as the main control equation for solving the rotor fuselage tail rotor interference flow field, and the Roe-MUSCL format is adopted for spatial discretization of the Reynolds averaged N-S equation; Select SST two-equation turbulence model or S-A turbulence model is selected as the turbulence model of the rotor fuselage tail rotor interference flow field.

6. The method of claim 5, wherein, In S4, The dual-time method is adopted for time stepping of the rotor fuselage tail rotor interference flow field, and the dual-time method includes physical time and pseudo time. The LU-SGS format is adopted for advancement in the pseudo time until the flow field fully converges. In the setting of the physical time, the time for the rotor blade to rotate 1° is selected as the physical time in the calculation process. After the rotor flow field basically converges, the time for the tail rotor blade to rotate 1° is selected as the physical time for numerical simulation until the flow field fully converges.

7. The method of claim 5, wherein the method further comprises: In S4, The far field boundary of the rotor fuselage tail rotor interference flow field is set as free flow, and the rotor fuselage tail rotor surface is set as wall surface.

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