Investigation of the 4-Quadrant behaviour of a mixed flow diffuser pump with CFD-methods and test rig evaluation

The complete pump characteristics including its 4-quadrant behaviour are of essential interest for off-design operations such as a pump trip. At this exceptional load case the pump enters the dissipation mode and moves further into the turbine mode while the direction of rotation and the flow direction will change. The time-consuming and expensive experimental investigation of the 4-quadrant behaviour requires a specific test rig, allowing the flow direction as well as the rotational direction of the investigated pump to be reverted. By measuring the pump performance (head and efficiency) at variable positive and negative discharge and rotation the complete pump characteristics are evaluated. Nowadays CFD- analysis allows for the reliable prediction of the hydraulic performance of a pump near the design point. However, abnormal operating conditions lead to complex and unsteady flow phenomena inside the pump. Besides steady-state calculations in the normal operating conditions quite comprehensive transient CFD-investigations are required to simulate the whole pump characteristics accurately. The present study focuses on the comparison of the results obtained on the test rig and by numerical methods and shows a remarkably good agreement between them. It can be shown that it is possible to reliably simulate the 4-quadrant behaviour of a mixed flow diffuser pump based on CFD-methods. Furthermore an exemplary waterhammer calculation shows the successful application of the numerically calculated 4- quadrant behaviour.