Lattice Boltzmann simulation of flow and sound fields around an axial flow fan

Abstract

Abstract In this study, not only the flow field but the aerodynamic sound field around the axial flow fan were directly simulated using the lattice Boltzmann method (LBM). To validate the LBM results obtained in this study, they were compared with the experimental results in terms of the pressure rise performance characteristics. In order to investigate the change in the flow and sound fields due to different operating points, calculations were conducted at two operating points; one is the low flow rate point where the fan is stalled and the other is the high flow rate point where the flow field in the fan is sound. In the comparison of the performance characteristics, the calculation results showed good agreement with the experimental results, and the flow fields were well reproduced with high accuracy. The analysis in terms of the vortical flow structures and the relative velocity distributions showed that the tip vortex was generated by the pressure difference between both sides of the fan blade at the high flow rate point while at the low flow rate point the flow field near the fan tip was covered with the low velocity region and the leading edge separation occurred on the tip side of the fan blade. Therefore, it was confirmed from the flow field as well as the performance that the fan blade was stalled with the blade loading lost at the low flow rate point. Large pressure fluctuations on the fan blade surface were caused by the interaction with the tip vortex from the adjacent blade at the high flow rate point and the occurrence of leading edge separation at the low flow rate point. With regard to the comparison of the far field sound spectrum, the calculation results for both two flow rate points were in good agreement with the experimental results in a low frequency range, and the aerodynamic sounds generated from the fan were predicted well with the LBM simulation.