Modification of a Radial Pump Characteristics With Fluid Suction in the Vaneless Space

Abstract Flow instability is a common unsteady phenomenon in the field of turbomachinery that often causes large pressure fluctuations, performance penalties, and strong noise as these machines operate under part-load operating conditions. Avoiding the flow instability as a hydro pump operates under such conditions, i.e., high head and small flow rate is usually difficult. Flow control methods such as fluid injection or suction can be applied to suppress, weaken, or delay the occurrence of flow instabilities in turbomachines. This paper presents results of a hydro pump flow control application with fluid suction (or removal) in order to modify the pump head (pressure ratio) vs. flow rate characteristics and to eliminate the regions of positive slopes so that pump operation becomes stable. Flow control with fluid suction from the vaneless space (between the runner and vaned diffuser) is applied on a model pump at HSLU (Lucerne University of Applied Sciences) Switzerland Hydro Laboratory at different diffuser opening angles. Flow suction is carried out using 10 holes (openings) distributed circumferentially in the vaneless space. The experimental work i.e., suction of fluid on the model pump at the test rig is supported with numerical (CFD) simulations of the tested low specific speed (nq = 25) radial pump. Numerical results are compared with the experimental data. The pump head – flow rate characteristics are first measured and calculated (CFD) without fluid suction for different diffuser opening angles. Then, flow control with fluid suction from the vaneless space is implemented and the pump head – flow rate characteristics are modified for different diffuser opening angles. The agreement between the experimental data and CFD predictions of the pump head – flow rate characteristics are good for the case without flow control and with fluid injection, but not satisfactory for the flow control case of fluid suction. The effect of flow suction or fluid removal in the vaneless space on the pump efficiency is also determined. Flow control with fluid suction results are also compared with the results of flow control with fluid injection experiments carried out during a previous research.