Hydrodynamics of Pump-Turbine at Off-Design Operating Condition in Generating Mode

Introduction

Unwished phenomena as strong vibrations, noises and strong cavitation levels accompany a pump-turbine in operating at off-design conditions. In order to study the sources of these phenomena, experimental and numerical flow investigations of a radial pump-turbine are performed under off-design operating conditions, involving speed no load, runaway and “S-shape” turbine brake curve.

Doctoral student : Vlad Hasmatuchi

Experimental “S-curves” in turbine operating mode

Preliminary experimental tests on a radial pump-turbine reduced model were performed at off-design operating conditions. The resulting “S-curves” at two different guide vane opening angles for referred machine are presented in the below figure. The machine behavior and the stability were observed during the operation in all tested operating points. Pressure fluctuations in different points from the machine’s walls were registered as well as the vibrations.

 S-Curves

After a preliminary analysis of the experimental results, by the help of the pressure fluctuations on different points from the machine, three operating points are selected for further investigations, as follows: a point in a quite calm operating region, a point near the runaway speed and a point near the zero discharge.

Numerical simulations are set up concordantly with selected operating points. The computational domain contains the entire machine starting with the spiral case, followed by the stay and guide vanes regions, the runner and the diffuser. In order to validate the simulations, comparisons with the experimental available data will be performed. Once the simulations being validated, a detailed analysis will be started to describe the phenomena trying to find the instabilities sources.