Aerodynamic Noise Analysis And Noise Reduction Design Of Axial Flow Fan Based On CFD/CAA

Axial flow fan is a kind of fluid machinery that is widely used in the cooling system of electronic equipment. With the popularization of electronic products and people’s enhanced awareness of noise pollution issue, the acoustic performance of axial flow fan is increasingly noticed. Noise has become a highly important factor of fan choosing and a key consideration of axial flow fan research, development and design. Reducing the noise while ensuring the original cooling capacity of axial flow fan has significant importance to the society. This thesis takes an axial flow fan as the research prototype. Based on the Computational Fluid Dynamics and Computational Aero-Acoustics theories, numerical simulation, and experimental investigation, the flow and acoustic field of the prototype fan are analyzed. Several noise reduction methods are put forward on the foundation of the above analysis. This paper mainly done the following work:(1) Research on the numerical simulation method of flow and acoustic field of the axial flow fan. The applicability of different turbulence models for the steady flow field and the aerodynamic noise prediction accuracy of unsteady RANS model as well as the large eddy simulation model are comparatively studied. RNG k-ε model is adopted for the steady simulation while the acoustic analogy method which combines LES model with the FW-H equation is used for the unsteady simulation ultimately. The methods and steps of building the geometric model and computational domain, meshing the grid and setting the boundary conditions are discussed in the process of establishing the simulation model. The static characteristic tests and acoustic tests are carried on to verify the rationality, feasibility and validity of the numerical simulation and the acquired conclusions.(2) Research on the characteristics of flow and acoustic field of the axial flow fan. According to the steady and transient simulations, regularities of distribution of some parameters, such as velocity, pressure, tubulence energy and vorticity have been acquired. The internal flow characteristic is obtained. The mechanism and location of aerodynamic noise sources are investigated by related acoustics principle along with the distribution of flow field. Also the directivity of the aerodynamic noise is researched. Through the analysis of noise monitoring points located at the leading edge, top and trailing edge of blade in different positions under three different rational speeds, the characteristics and distribution law of aerodynamic noise are grasped.(3) Research on the noise reduction and optimal design of the prototype fan. The influence of fans with different tip clearance, splitter blades, and perforated blades on the flow and acoustic field are studied separately on the basis of analysis of the mechanism and location of aerodynamic noise sources. The corresponding retrofit schemes are proposed and the variation of the flow field compared with the original prototype is discussed. The mechanism of the retrofit design schemes is explained particularly. The substantial objects are manufactured and the noise reduction range and effect at different working conditions are investigated by both numerical forecasts and experiments. The applicability and characteristics of the discussed noise reduction design schemes are summed up.