Experimental Investigation of the Flow Behaviour Inside a Centrifugal Impeller Channel at Design and Off-Design Flow Rates
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An experimental study of the flow behavior inside the channels of an 8-blade backswept low specific speed impeller at design and off-design conditions is presented. The measurements took place at both the inlet and the outlet of the impeller channel at the mid height of the channel passage. The particle image velocimetry (PIV) technique was used to measure the velocity components in the inlet and outlet frames of the impeller channel. The flow behavior inside the channel, the mean normalized primary and secondary velocity components at six radial locations inside the channels, and turbulence intensity in terms of the variation in the relative velocity components were investigated at the design condition, 75%, 50%, 40%, 30% and 25% of the design flow rate. The results demonstrated a well behaved flow with no evidence of flow separation at the design condition. The fluid flow inside the impeller channel started experiencing a flow separation, when the flow rate is reduced, which propagated throughout the channel passage and caused the channel to stall with a large recirculation zone at severe off-design flow rates.