Low specific speed centrifugal pump with the characteristics of small flow, high head, compact structure is often used in many areas such as chemical industry and aerospace which has the extremely high request to the efficient and vibration performance. Generally, the flow passages of the impellers are rather long and narrow. Under the combined influence of the deceleration and the Coriolis force, the outlet velocity distribution of impeller is uneven which contains a wake flow with lower velocity near the suction side of blades. The consequent circumferential nonuniformity of the impeller outflow lead to the instability of flow field and energy loss due to mixing through exchange of momentum which deteriorate the performance of pressure pulsation and efficiency. Also due to the existence of low-energy fluid on the suction surface, the velocity at the outlet of the impeller deviates to the suction surface, resulting in velocity slip which cause the decrease of pump head. Thus, the key to improve pump performance is to suppress the wake to make the outlet velocity more uniform.

In previous studies, increasing the blade outlet angle, reducing the flow rate and increasing the rotating speed will strengthen the wake structure and deteriorate the performance of pumps. Therefore, many researchers have summarized some methods to depress the wake flow. Backward curvature of the blades can eliminate or reduce the extent of the jet and wake flow configuration. The bias of split blades can effectively prevent the formation of the wake zone and improve the performance of the pump by reducing the influence of reverse vortex. Trailing edge profiling technology which is commonly used in the optimization design of centrifugal pumps can improve head, efficiency and pressure pulsation performance of pumps. Gulich indicated that the efficiency increase of pump was attributed to the narrowing of the wake following off the TE. Optimization the distribution of blades thickness also can repress the internal secondary flow and alleviate pressure pulsation of low specific speed centrifugal pumps.

It can be seen that reasonable blade design is very important to suppress wake effect and improve the performance of pumps. Driving by the pressure difference between blade surface, low-energy flows in the boundary layer tends to accumulated to the suction surface to form a wake. Given that the key to depress the wake is to eliminate the pressure difference between blade surface on the tailing edge. Through the design of blade thickness distribution, the blade angle of each side can be changed to control the pressure distribution on blade surface.

In this study, the hydraulic and dynamic performance a low specific-speed centrifugal pump was investigated by both numerical simulation and experimental. Three different impellers are designed with different thickness distributions along the same mean line of the blades. Given that the existence of wake flow results in large mixing loss and velocity deviation at the blade outlet. Entropy generation rate and velocity slip coefficient are introduced here to measure the wake loss and wake structure. Results show that thicken the middle of the blade appropriately can improve the efficiency and pressure pulsation characteristics of the centrifugal pump. Through CFD analyses, compare with the original impeller, both the entropy generation rate and the velocity slip at the impeller outlet of the optimized impeller are decreased which means the wake flow was effectively suppressed.


Design of Blade Thickness Distribution on Wake Suppression for Low Specific Centrifugal Pump

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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