Computational research on the formation mechanism of double humps in pump–turbines

Abstract

The hump formation mechanism has not been fully understood so far, mainly because of two difficulties in analysis. The first one is how to find the most important external characteristic factor inducing humps, and the other is how to avoid too many assumptions when analysing the change in the runner’s capacity for work (the direct use of Euler’s formula makes too many assumptions). This paper proposes a new method based on the second derivative of the external characteristics to identify the most critical factor inducing humps quantitatively. The runner blades’ capacity for work is calculated and shown as a cloud diagram using as few assumptions as possible to help understand the actual relationship between flow fields and humps. Additionally, the importance of stall in affecting the runner’s capacity for work is analysed and explained. Thus, the double hump formation mechanism in pump–turbines has finally been understood.