NOISE QUALITY CONTROL OF SMALL HIGH SPEED WATER PUMP BY REDUCING SEPARATED FLOW

摘要

The small type high rotating speed water pump which have inverter for rotating speed control have been served as a monitor product and are more quiet than those with constant rotating speed which install flow control valve. Blade passing frequency tone and some flow noise of valves were completely decreased. However, some annoying flow noise is closed up as the ordinal noise of pumps have become quiet. This annoying noise source and the generation mechanism have been experimentally studied. This pump has a centrifugal flow impeller and a return type diffuser with in-line flow. Studies of sound intensity distribution around the pump indicated that this annoying noise was radiated from the diffuser portion. And studies of the flow visualization by an oil-film method in the pumps indicated that some separated flow were generated at the return type diffuser. It was made clear by these studies that the diffuser flow generated separated flow and radiated the annoying noise. The improved pump with smoothed diffuser decrease the annoying noise although noise spectra and noise level do not remarkably change. The analysis of sound quality with respect to this pumps noise have been examined and it has been recognized that "Loudness level" and "Sharpness" are remarkably decreased. It is concluded that the reduction of separated flow on the return type diffuser induced the decrease of "Loudness level" and "Sharpness" with respect to noise from the small high speed pumps. Finally, small high speed pump as the practical product do not install the return type diffuser for reducing pressure loss and annoying flow noise.