Analysis of secondary flow behavior in low solidity cascade diffuser of a centrifugal blower (1st Report, effect of radial location of blade leading edge)

This paper deals with the effect of the blade leading edge location of low solidity cascade diffuser (LSD) on noise and diffuser performance in a centrifugal blower. The noise of the vaneless diffuser, varied little in a wide flow rate range, on the other hand, that of the LSD increased remarkably as the flow rate decreased. Two kinds of discrete frequency noise appeared due to interaction between the rotating jet-wake flow and the LSD blade and another interaction between the rotating impeller blades and the reverse flow toward the impeller exit, however, it was found that the LSD noise was mainly dominated by the broadband noise. By shifting the LSD blade leading edge location downstream from R_LSD = 1.10 to 1.20, the noise was reduced by about 3 dB at maximum without deterioration of the diffuser performance. The mechanism being able to maintain the high pressure recovery was pursued in view point of formation of the recirculating secondary flow.