Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Conditions

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficulty in conducting experiments at elevated pressure and temperature working conditions, computational fluid dynamics (CFD) simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviations from experimental results for the flows of steam-only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number conditions. The predicted results show an off-center cooling enhancement with a local maximum of 100% at $s/d=2$ and an average cooling enhancement of about 50%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.