Abstract
In recent years, energy saving of fluid machinery, such as a centrifugal compressor, is desired, and the improvements of efficiency for each part are demanded. In a vaneless diffuser of a centrifugal fan and compressor, however, a rotating stall may occur and result in an unstable operation. Accordingly, various degradations may appear, e. g. a pressure performance drop, noise/vibration occurrences and damage of machines. The rotating stall is one of rotational flow instability, i.e. is induced by a rotating fluid. Therefore, in this research, the flow around the rotation circular cylinder between two stationary circular disks was investigated by experiments, which is a model of a centrifugal vaneless diffuser without discharge from and suction in an impeller. The experimental FFT results show several peaks with small frequencies, which indicates the flow instabilities can occur with neither discharge nor suction.
