Numerical Analysis Of Aircraft Rotor Aerodynamic Noise Based On Massively Parallel Computing

In recent years,the aerodynamic noise problem of rotorcraft has received increasing attention from the academic community.With the gradually clear application prospect of small rotor-type UAVs and the design demand of future-oriented green vehicles,the need for aerodynamic noise analysis is becoming more and more urgent.The problem of numerical simulation of rotorcraft aerodynamic noise is challenging because it involves irregular,multi-scale,rotational motion,unsteady turbulent flow in both time and space and the mutual interference between the random motion of turbulent flow and rotor blades in the flow field.In this paper,a set of high-performance numerical simulation methods suitable for the aerodynamic noise study of rotor-type UAV is developed through the study of computational fluid dynamics and computational aeroacoustics numerical simulation methods.The accuracy of the algorithm is verified by using a benchmark test case of a single-rotor UAV,and finally the method is applied to the numerical simulation of the aerodynamic noise of a quadrotor UAV to obtain detailed flow field and aerodynamic noise of the whole UAV.The accurate capture of turbulence in a rotating fluid plays a key role in the accurate aerodynamic noise calculation.In this paper,we firstly investigate a high-quality mesh generation method suitable for high-fidelity numerical simulation of rotating fluid mechanics,and developed a set of effective mesh generation methods for numerical simulation of rotating fluid mechanics.Compared with the traditional uniform mesh generation methods,this method greatly reduces the total number of mesh cells and computational cost while ensuring that the rotor shape and computational accuracy can be accurately portrayed,which in turn improves the overall aerodynamic noise computation efficiency.Due to the cyclic rotational motion of the rotor,there is a certain flow separation phenomenon at the rotor surface,so it is not easy to be accurately simulated near the rotor surface.In order to solve this problem,several turbulence models are studied and the k-? SST turbulence model is finally chosen to deal with the turbulence near the surface after a deep comparison and analysis.k-? turbulence model not only solves the flow at the surface accurately,but also overcomes the sensitivity of boundary conditions and converges faster.In addition,the rotor surface,being a complex surface,requires a fine enough mesh to accurately capture the rotor's airfoil when generate the mesh so that the flow field around it can be accurately simulated.Due to the restriction of the numerical stability condition of the unsteady hydrodynamic equations,the time step size for the temporal discretization needs to match the minimum mesh size in the space discretization,thus requiring a very small time step size,which leads to an increase in the total simulation time.To solve this problem,this paper explores the PIMPLE algorithm in fluid dynamics simulation,which effectively overcomes the limitation of the algorithm on the time step size and ensures the stability of the algorithm while reducing the simulation time.After the completion of the flow simulation,based on the flow field results,this paper explores the numerical calculation method of aerodynamic noise based on the FW-H equation,and verifies its accuracy with a benchmark test case of a single rotor.The numerical results have a good agreement with the experimental results,and the error between the calculated sound pressure level at the first BPF and the experimental results is less than 5 dB.After the algorithm was verified,it was further applied to the analysis of the aerodynamic noise of the whole UAV,and the direction of the optimization of the aerodynamic noise of the rotor-type UAV was obtained.The main innovations of the paper are:(1)a set of high-performance numerical simulation methods for high-fidelity simulation of rotor-type UAV aerodynamic noise is developed,and the accuracy and computational efficiency of the algorithm are studied;(2)a set of high quality mesh generation methods suitable for high resolution numerical simulation of rotational fluid dynamics is developed;(3)the numerical aerodynamic noise simulation of the whole quadrotor UAV was realized and detailed flow field and aerodynamic noise results were obtained.