Investigation and modeling of two phase flow through a compressor stage: Analysis of film breakup

For stationary gas turbines, the injection of water sprays into the compressor inlet is used to increase the power output, which can be used for rapid correction of power fluctuations appearing in power supply systems with today's increased use of wind and solar energy. However, to fully utilize this technique a comprehensive understanding of the underlying phenomena is needed. An inhouse CFD program was used at Institute of Aerospace Thermodynamics (ITLR) Stuttgart modeling a variety of two-phase phenomena which was validated on the transonic wind tunnel at Helmut Schmidt University (HSU) Hamburg. The present paper focuses on the water film on the blades formed by water deposition of impinged droplets. Experimental results using a reflective shadowgraphy method reveal the wall film pattern on the blade without disturbing the flow. A numerical model is presented predicting the position of film breakup based on the superposition of a small perturbation of the film height. The onset of film breakup is predicted to be at the position in which the perturbation is not dampened by the acting forces. The film breakup position is analyzed experimentally and numerically for three different water loads. The experimental analysis shows that the onset of film breakup is almost independent of the water load. The numerical model shows the same trends and indicates a film breakup at the same position.