Numerical Study On Characteristics Of Aerodynamic Noise Distribution Of An Axial Flow

Prediction of fan aerodynamic noise is the most popular and is also one of the much more difficult issues currently in fluid machinery research domains. The mine axial auxiliary fan is studied in this essay. In this study, simulation of the unsteady turbulent flow field in the fan was proceeded employing the finite volume method. Numerical prediction of the aerodynamic noise in the fan was performed by utilizing the method of CFD. By using the finite element method, the modal of the fan shell also was calculated. Major achievements of this thesis are as follows:Firstly, geometrical model of the fan whole flow field was built, which is from the inlet of the collector to the outlet of the diffuser, and the governing equations of the three-dimensional unsteady turbulent flow field was deduced too. In order to make the numerical calculation can be fully and truly reflect the interaction between the impeller and the adjacent stationary components, the appropriate dynamic and static interfaces type was set.Scondly, the entire flow field was considered to be the simulation domain, and the computational grid was partition generated, then the proper turbulence model was selected, lastly given a reasonable boundary conditions. According to the above conditions, steady flow calculation was fulfilled. Unsteady flow structure and changes of pressure with time were obtained based on the unsteady turbulent flow field, and which was acquired by employing the result of the steady simulation as the initial condition.Thirdly, the distribution of the aeroacoustics power of the fan was predicted under the improved Broadband Sound Sources model which was proposed by Proudma according to the steady flow calculations. Based on the unsteady simulation Fast Fourier Transform (FFT) method, the distribution of pressure fluctuation in time domain and frequency domain on the monitoring points belong to the two surfaces between the impeller and the guide vane was gained. The characteristic of the aerodynamic noise in the fan was simulated by using the large eddy simulation technique and FW-H noise model. The radial pressure on the shell from flow field calculation results was loaded into FEA software as the known conditions of the dynamic response analysis. Modal analysis of the Shell was done here.Finally, conclusions were obtained through this research. The impeller flow passages produce the mainly flow losses, and being the major generating parts of fan aerodynamic noise source. Overally, Sound Pressure Level (SPL) at the tip clearance is greater than anyother part of the fan, SPL at the impeller outlet is greater than it at the impeller inlet, and SPL at the second stage impeller is also greater than it at the first stage impeller. Showed by the shell modal analysis, the fluctuating forces on the shell vibration mode was less affected.