Numerical and Experimental Investigation of Trailing Edge Modifications of Centrifugal Wastewater Pump Impellers

Centrifugal pump impellers for wastewater applications have to be designed to meet additional requirements compared to clearwater pumps. Therefore these impellers usually have only one to three relatively thick blades and large width to diameter ratios. The presented study deals with the effect of trailing edge modifications, especially under-filing, to this class of impellers. Two wastewater pump impellers with different specific speeds have been investigated numerically and a detailed loss analysis has been made for the impellers with default and modified trailing edge configurations. In case of the impeller with lower specific speed the head but not the efficiency could be increased by trailing edge under-filing. For the impeller with higher specific speed, under-filing resulted in an significant increase in head and efficiency. The analysis of the losses showed how the losses in different sections of the impeller are affected by the trailing edge modifications and how and under what circumstances the efficiency can be increased in this way. Experiments on the test rig confirmed the numerical results and stated an increase in head of 7.7 percent at no increase in efficiency for the impeller with the lower specific speed and an increase in head of 11.7 percent at an efficiency gain of 1.7 percent at the design flow-rate and even 4.4 percent increase in maximum efficiency for the impeller with higher specific speed.