Turbomachinery

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Recently noise reduction of small axial flow fan for cooling electronic devices is required. When obstacle such as grid for turbulence is located in front of fan, noise of axial flow fan becomes higher. In this study, numerical simulations were conducted by using LES (Large Eddy Simulation) with DSM (Dynamic Smagorinsky Model) about axial flow small fan in order to clarify noise increase mechanism with grid for turbulence. Flow pattern around fan blades and pressure fluctuation on fan blade surfaces were compared under conditions of with or without grid for turbulence. Fan noise with grid for turbulence is higher 4 dB(A)than noise without grid for turbulence at flow rate Q=0.033 m³/s. Pressure fluctuation at pressure side surface of blades with grid for turbulence becomes high compared with pressure fluctuation without grid for turbulence. Change of attack angle to blade leading edge increases by turbulence generated by grid for turbulence, which increased pressure fluctuation on pressure side blade surface.

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