Blade Number Influence on Centrifugal Impeller Flow Behavior
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In this study, experiments were conducted to observe the performance and flow structure of the fluid inside the passage of 5 and 7 bladed impellers. The main purpose is to understand the influence of the number of blades on the performance and flow behavior of a centrifugal impeller. To analyze the flow behavior, the particle image velocimetry (PIV) technique that is known as a non-intrusive velocity measurements method was used. Fluid flow streamlines, mean normalized primary and secondary velocity, turbulence intensity (TI) and fluid angle deviation were presented to understand the fluid flow behavior. The results showed that the head rise of the fluid inside the 5 bladed impeller is lower than the 7 bladed impeller. However, the efficiency showed a similar value between the 5 and 7 bladed impeller. The PIV results showed that even though the 7 bladed impeller produced higher head rise, the losses were also higher. PIV results also showed that the influence of the number of blades on the fluid behavior was less at a high flow rate and more obvious at low flow rate. Some significant differences of fluid behavior between the 5 and 7 bladed impellers were found. At the design flow rate, for the 5 bladed impeller, a well behaved flow structure was found. In comparison, there was separation flow on the blade pressure surface of the 7 bladed impeller that was probably caused by the high 'angle of attack'. In addition, a jet pattern that occurred near the exit of the blade pressure side appeared to be stronger for the 5 bladed impeller than the 7 bladed impeller. At low flow rates, the wake region that appeared on the blade suction side was larger for the 7 bladed impeller. Finally, PIV measurements conducted in this study showed similarity in the performance result and flow structure with the several past studies obtained using other method measurements and visualizations. The ease and accurate results of PIV measurements suggest that this method is a potential tool to observe fluid flow inside the impeller in more detail for future studies.