Investigation of steam film cooling enhancement of cylindrical and fan-shaped holes on a hydrogen gas turbine vane with mist injections

In this study, the mist/steam film-cooling performance on a guide vane of the hydrogen gas turbine with cylindrical and fan-shaped holes operating under actual service conditions was numerically studied. A single film hole model near the vane leading edge, arranged separately on the pressure and suction surfaces (PS and SS), was examined. The implementation of the two-parameter Realizable k-ε turbulence model with a phase-coupled Lagrangian stochastic tracking method provided satisfactory agreement between numerical predictions and experimental results for mist/air cooling, and was selected as the baseline. The effects of the mist proportion (5%, 10%, and 15%), and water droplet diameter (5, 10, 15, and 20 μm), as well as its distribution (uniform and R-R nonuniform) on mist/steam adiabatic film cooling effectiveness, and droplet dynamics in a single vane cascade were analyzed in detail. The lateral and area-averaged steam film cooling effectiveness, with and without mist, on PS and SS, with three blowing ratios varying from 0.5 to 1.5, was compared. The results indicate that mist significantly enhances the steam FCE, especially for the cylindrical hole at a small blowing ratio of 0.5, with up to 29% at PS. At higher blowing ratios, the film coverage effect in the region close to the hole of the cylindrical case at PS is impaired due to the film-cooling lift-off. With increasing mist proportion, the mist/steam film cooling effectiveness for cylinder and fan-shaped holes slightly increases, and its highest value reaches approximately 0.24 and 0.4 for the fan-shaped hole at a blowing ratio of 1.0 on PS and SS, respectively. The water droplet size and distribution have little effect on the average mist/steam film cooling effectiveness. However, they significantly affect droplet trajectories along the vane surface due to the kidney vortex.