Visualization of Unsteady Flow in a Multistage Helico-Axial Pump
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Helico-axial pumps are designed to pump mixtures of gas and liquid. Secondary flows and rotor-stator interactions are known to add complexity to the flow field in unshrouded axial-flow turbomachinery. Here we use a high-speed camera to visualize the internal flow field in a multistage helico-axial pump. A wide range of relative flow rates are investigated to see how secondary flows emerge and evolve depending on the operating point. Nitrogen bubbles are used as tracers to obtain a qualitative understanding of the flow. The recordings exhibit a highly unsteady flow field that varies with the relative flow rate. The tip leakage flow and interactions between the components lead to recirculation and reversed flow, also when operating near the best efficiency point. Local gas accumulation and stagnant fluid was observed near the impeller outlet at very low relative flow rate, where the slope of the head-flow curve had shifted.