Analysis of secondary flow behavior in low solidity cascade diffuser of a centrifugal blower (2nd report, effect of blade tip groove near leading edge)

A low solidity cascade diffuser (LSD) shows features of a wide operating range and a high pressure ratio, however, a high level of noise. The first objective of the present study is to show that the noise can be reduced effectively without deterioration of the LSD performance by means of a small tip-groove located at the shroud side alone, and the second one is to clarify the mechanism being able to achieve high blade loading without stall even under the large attack angle of 15 degrees. By analyzing the flow in the diffuser numerically, the effect of a small tip-groove on the stagnation area near the LSD blade leading edge, the vortex generated in the tip-groove and the secondary flow behavior were investigated. It was found that the formation of circumferentially moving secondary flow generated by the vortex in the shroud tip-groove is a key factor of the high LSD performance. Finally, an optimum tip-groove configuration was proposed.