Flow around Fan Blade and Pressure Fluctuation on Blade Surface of Small Axial Fan with Obstacle near Inlet

Abstract

Numerical simulations were conducted by using LES(Large Eddy Simulation) with DSM(Dynamic Smagorinsky Model) about the axial flow small fan for cooling electronic devices. In this study, the tested fan has two kinds of obstacles located in the suction side. One obstacle is infinite plate(Infinite model)，the other obstacle is half of infinite plate which covers lower half region of fan(Half model). Distance from the fan to the obstacles is 20 mm. The flow pattern around the fan blades and RMS of pressure fluctuation on the fan blade surfaces were compared under the conditions of with and without obstacle. The flow direction into fan was axial under the condition of without obstacle. On the other hand the flow direction into fan was radial under the condition of with obstacle. This radial inflow caused the expansion of negative pressure region due to the separation from the top of casing, which enlarged tip vortex region and increased pressure fluctuation on suction side blade surface. Moreover the radial inflow caused the reduction of axial flow velocity at the blade tip, which increased pressure fluctuation on pressure side blade surface due to the interference between tip vortex and blade surface. The radial inflow and the axial inflow were mixed in the half model. As the result, fan static pressure, fan noise and pressure fluctuation have interim characteristic of no obstacle model and infinite plate model.