Numerical Study On Hydrodynamic And Acoustic Performance Of Bionic Cylinder

As one of the hot issues in recent years,drag reduction and noise reduction is particularly important in the development of underwater vehicles.The movement of the protruding structure on underwater vehicle generates the flow around bluff body.This flow can cause not only generate resistance during navigation,but also flow noise.The flow around bluff body limites the speeed of underwater vehicle and reduces its concealment.Therefore,it is important to research how to effectively reduce the resistance and control the noise.Firstly,based on the three-dimensional flow around an airfoil cylinder,the correctness of the numerical simulation method of the initial model is verified by Lighthill Acoustic Analogy and Large eddy simulation.The stability and accuracy of flow field calculation were verified by dividing three flow field grids and comparing the Drag Coefficient and S_tnumber.Then,the flow field results were used as sound sources to divide three grids of sound fields,and the total sound pressure levels at different monitoring points were compared to verify the accuracy of sound field calculation.Furthermore,it is proved that the method of large eddy simulation combined with Lighthill acoustic analogy is correct.Furthermore,by observing the characteristics of birds’feathers,fins and other structures,based on the bionic idea,the straight airfoil cylinder was modified to design,and A total of 16 kinds of three-dimensional cylinder models with bionic appendages in three categories A,B and C were designed.The hydrodynamic characteristics of the bionic cylinder are analyzed.The results show that the type C bionic cylinder has better drag reduction effect,with the maximum drag reduction rate of 9.35%.The drag reduction mechanism of the bionic cylinder is explained from the aspects of vortex characteristics of wake field and pressure pulsation.Finally,the bionic cylinder with better hydrodynamic performance is selected.Based on the results of transient flow field,the sound field characteristics of bionic cylinder are solved by using actran.The sound pressure spectrum characteristics of different cylinder models are compared,and the noise reduction effect of bionic cylinder is analyzed.Among them,C3 bionic cylinder has better noise reduction effect,and the maximum noise reduction is about 3.8d B.The noise reduction mechanism of the bionic cylinder is analyzed from the aspects of acoustic directivity,lift coefficient and acoustic pressure nephogram,which provides a reference for the parameters and shape optimization of the bionic structure.