Suction recirculation is caused by flow incidence angles that are significantly dissimilar to the inlet vane geometry. The stalled area on the inlet vane produces a hydraulic instability, resulting in the formation of fluid swirl.
Large inlet areas magnify the formation of fluid swirl as the fluid has enough “room” to recirculate. When severe, the fluid circulates out of the impeller eye and interferes with normal suction flow.
The detriments of suction recirculation are two-fold. First, the fluid swirl can cause the suction pressure to fall below the fluid vapor pressure, creating vapor bubbles. With changing pressure fields, the bubbles implode and release energy. If this collapse occurs on the vane itself, material damage can result. This is known as separation and/or cavitation which reduces the operating life of the impeller.
