The Application And Research Of The Unstructured Grid FVM In The Computational Fluid Acoustics

Flow-induced noise which is often found in people's livelihood,aviation,marine and industrial applications is one of the most common sources of noise in the people's everyday life and the nature.The work of understanding,predicting and ultimately controling flow-induced noise is becoming increasingly important,and causes academic community and the aviation,marine and industrial applications sector increasing attention.The key elements in numerical simulation of flow-induced noise consist of the method for predicted flow-induced noise,spatial and temporal discretization schemes and nonreflecting boundary.The main objective of the present thesis is the development of suitable numerical methods for flow-indeced noise applications including the study of sound propagation,far-field acoustic characteristics and flow-induced noise generation mechanism and propagation process.In order to verify the feasibility of using the method of computational:fluid dynamics to solve the flow-induced noise problems,a pre-processor for sound propagation in the static flow is developed.The governing acoustic equations are discretized over finite volume of unstructured meshes,and the transient,convection and diffusion term is discreted by the second-order Euler implicit scheme,TVD-SUPERBEE scheme and central difference,respectively.The acoustic pressure-particle velocity coupling is solved by SIMPLE algorithm.The software can be used to slove the sound propagation problem through any media in the static flow by user-defined the media.For FW-H equation which is one of the most widely method solving the flow-induced noise problem,the detailed derivation process is understood to study the scope for FW-H equation.An interior surface approximation method solving the penetrable sound source integral surface problem is proposed.If different inergral surfaces are usd in the same case,the method could reduce large workload for remeshing rather than the interior boundary method in the commercial software,while avoiding errors coused by using interpolation in the surface of the sound source integration at the flow field.For flow-induced noise problems at a low Mach number flow,a decomposition technique which the compressible N-S equation is divided into incompressible N-S equation and the perturbation equation is introduced.The final perturbation equation transformed to use the transitional vector has the same form with N-S equation.The governing perturbation equation is discretized over finite volume of unstructured meshes.The convection and source terms treatment methods are discussed in detail.And the SIMPLE algorithm is extended to solve acoustic perturbation equations.Acoustic nonreflecting boundaries are solved by high precision radiation nonreflecting boundaries and perfectly matched layer absorbing boundary,because computational domain is much smaller compared to the physical area and the boundary question results can not affect the computational domain simulation.Using the implicit scheme to solve the transient term and finite volume method to discrete nonreflecting radiation boundary equation,unify to solve discrete boundaries and internal unit equations.Based on the acoustic perturbation equations,acoustic perfectly matched layer equation and transform coefficients are found.The computational domain is decomposed into two regions including acoustic perturbation zone and perfectly mateched layer zone.The surface marched with the two region is achieved coupling solution.The computational fluid acoustics technologies are implemented in an in-house software which bases on unstructured grid using finite volume method.The software requirements analysis,design,and program implementation process are discussed in detail.To avoid secondary calculation,the coupling solution with the splitting method and FW-H equation is achieved to solve the flow-induced noise problem by flowing past a wall.And the near-field and far-field acoustic characteristics can be got simultaneity.The work demonstrated that the developed software can be used for the simulation and analysis of flow-induced noise at a low speed flow.