Abstract
Detailed optical measurements for the flow inside rotating passages of a five-bladed centrifugal impeller were performed by particle image velocimetry (PIV). The flow in mid-plane perpendicular to the pump axis was measured at 1400 r/min rotation speed. Seven flow rates, namely, 1.2, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 Qd, were surveyed. The averaged PIV velocity maps and streamline were analyzed. Results show that when flow rate decreases to 0.8 Qd, the flow separation forms initially at the blade suction side in passage 1. With decreasing of flow rate, the flow separation appears in much more passage, the separation region enlarges, and the flow at the pressure side begins to form flow separation. All passages are gradually occupied by the vortices generated by flow separation, until the passages are finally blocked. The scale of vortex along the stream-wise direction at the suction side is larger than that at the pressure side, whereas the scale of vortex along the span-wise direction is smaller than that at the pressure side. With the decrease in flow rate, the scales of vortices at the suction and pressure sides increase, and the vortices at both sides move toward the inlet and outlet, respectively. Moreover, the effect of vortices on the tangential and radial components of the absolute velocity was analyzed.
Highlights
The flow inside a centrifugal impeller is complicated due to the curvature and rotation of the blade,1–6 and the theoretical and experimental study on internal flow is advancing.7–13 Particle image velocimetry (PIV) has been widely used as a measuring approach to investigate the internal flow of centrifugal pumps for its nondisturbance on flow velocity
The external characteristic of the experimental pump was characterized before the PIV experiment
When the flow rate is 0.8 Qd, a low velocity region close to the blade suction side appears in flow passage 5, which extends from 1/4 location of the suction side inlet to outlet accompanied by a clockwise separation vortex
Summary
The flow inside a centrifugal impeller is complicated due to the curvature and rotation of the blade, and the theoretical and experimental study on internal flow is advancing. Particle image velocimetry (PIV) has been widely used as a measuring approach to investigate the internal flow of centrifugal pumps for its nondisturbance on flow velocity. Keller et al. adopted PIV to analyze the unsteady flow field near the volute tongue region at high flow rate. They obtained the shedding of wake vortex at the trailing edge of the impeller blade, its influence on the volute tongue, and its evolution process. Sinha and Katz measured the flow field of centrifugal pump near the design flow rate. They acquired the average velocity, vorticity field, and corresponding turbulent stress distribution at different impeller blades. By analyzing the streamline of the velocity field, the variation of the scale and position of vortex in the flow passage with flow rate is evaluated under the same rotation speed, and the effects of vorticity on the pump head and impeller passage through-flow are investigated
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