Flows in the Vaneless Radial Diffuser Operating at Lower Flow Rates : 1st Report, Flow Visualization and Pressure Variations in the Radial Diffuser without Volute Casing

Experiments for water flows using flow visualization techniques and for air flows using some conventional instruments were conducted on the vaneless diffusers. The rotating stall cells were confirmed in the region of lower flow rates in the vaneless radial diffuser, and the flow characteristic parameters of existence of the rotating stall cells were attained for various space widths between the impeller open face and lower diffuser side wall. The relationships between the variations in pressure and the traveling speeds of the stall cells were also shown. The pressure distributions in the vaneless diffuser can be represented by an empirical relation for the outer range of normal operating flow rates