Evaporation Modeling of Water Droplets in a Transonic Compressor Cascade under Fogging Conditions

Abstract

High-fogging is widely used to rapidly increase the power outputs of stationary gas turbines. Therefore, water droplets are injected into the inflow air, and a considerable number enter the compressor. Within this paper, the primary process of droplet evaporation is investigated closely. A short discussion about the influential parameters ascribes a major significance to the slip velocity between ambient gas flow and droplets. Hence, experimental results from a transonic compressor cascade are shown to evaluate the conditions in real high-fogging applications. The measured parameter range is used for direct numerical simulations to extract evaporation rates depending on inflow conditions and relative humidity of the air flow. Finally, an applicable correlation for the Sherwood number in the form of S h ( R e 1 / 2 S c 1 / 3 ) is suggested.

Two-Phase Flow Phenomena in Gas Turbine Compressors with a Focus on Experimental Investigation of Trailing Edge Disintegration

“…This can be explained by their relaxation behavior. Analytic estimations considering drag of the droplets show that the limit for perfect relaxation within the characteristic length of a compressor blade lies at D ≈ 25 µm [5]. Thus, larger droplets are not able to follow the curved streamlines around the compressor blade and thus might hit the surface.…”