Incipient Cavitation in a Bulb Turbine: Model Test and CFD Calculation

Abstract

For a certain operating point of a horizontal shaft bulb turbine (i.e. volume flow, net head, blade angle, guide vane angle) the efficiency for different pressure levels (i.e. different Thoma-coefficient σ) is calculated using a commercial Computational Fluid Dynamics (CFD-)-code including two-phase flow and a cavitation model. The results are compared with experimental results achieved at a closed loop test rig for model turbines.The comparison of the experimentally and numerically obtained efficiency and the visual impression of the cavitation show a good agreement. Especially the drop in efficiency is calculated with satisfying accuracy. This drop in efficiency in combination with the visual impression is of high practical importance since it contributes to determine the admissible cavitation in a bulb-turbine. It is seen that the incipient cavitation in Kaplan type turbines has no major importance in determing this admissible amount of cavitation.

Prediction of incipient cavitation in micro tubular propeller turbine

“…A mixed-flow turbine is also not free from cavitation, and has been studied about cavitation caused by the tip leakage flow using numerical analysis [9]. Similarly, research on the cavitation of a bulb turbine has been conducted through experiments and numerical analysis [10]. In addition, investigations of cavitation in Pelton turbine [11] and cross-flow turbine [12] were performed.…”