Investigation of Applicability of Transporting Water Mist for Cooling Turbine Blades

Abstract

This paper presents a numerical study to investigate the feasibility of transporting water mist to the rotating blades of a high pressure turbine. The idea of using mist film cooling to enhance conventional air cooling has been proven to be a feasible technique under laboratory conditions. However, there are challenges in implementing this scheme for real gas turbine systems. The first challenge is how to transport the mist to the rotating blades and the second challenge is delivering the mist to the injection holes and getting the particles to survive within the harsh gas turbine environment. Both a zero-dimensional mist evaporation analytical model and a 3D computational fluid dynamics (CFD) scheme are employed for analysis. In the CFD simulation, the Lagrangian-Eulerian method is used along with the discrete phase model (DPM) to track the evaporation process of each individual water droplet. For transporting the mist to the blades, the high-pressure water mist is injected into the stream of cooling air extracted from the compressor through two different passages. The first passage passes through the rotor cover-plate cavity before entering the blade base. The second passage passes through a diaphragm box on the base of the second vane, then tangentially through a cooling passage in the rotating shaft, and eventually to the blade base. The results show that it is feasible to transport the mist from the turbine casing to the blade through both passages, provided that droplets with sufficient particle diameter and mist loading are used. The shorter passage, through the nozzle diaphragm, alleviates a lot of challenges facing the passage through the blade cavity, and seems to be more practical. A side benefit of transporting mist through the internal passages is the additional cooling of the pre-swirler and rotor cover plates. The results are encouraging for implementing the mist cooling technique under real gas turbine conditions.

Effects of operating conditions on flow and heat transfer characteristics of mist cooling in a square ribbed channel

“…It is found that different coolants have insignificant influence on morphology and distribution of secondary flows. Meanwhile, the velocity contour plots I did not see the plots of these secondary flows suggest that the velocity in mist/steam cooling and mist/air cooling ribbed channel is slightly lower than that in corresponding steam cooling and air cooling channel, due to the entrainment effect of water droplets when the water droplets are suspended in the flow and transported by steam and air flow via drag [18]. However, the decrease of velocity in mist/steam and mist/air cooling channel is minimal due to a small mist mass ratio (only 2% mist) in this study.…”

“…Theoretically, it is encouraging for applying mist cooling to both gas turbine vane and blade under elevated operating conditions; and the performance of mist cooling has been moderately investigated. Wang et al [17,18] explored explore the feasibility of applying mist cooling to gas turbine vanes and blades by numerical simulation method. The results demonstrated that theoretically, it was encouraging for applying mist cooling to both gas turbine vane and blade under elevated operating conditions.…”