Influence of mist droplet injection and blowing ratio on mist/steam showerhead film cooling on a first-stage vane of hydrogen gas turbine

• The mist-assisted steam film cooling on a hydrogen gas turbine vane is studied. • The influences of mist concentration, droplet size, and blowing ratio were analyzed. • Mist concentration has a slight effect on FCE at the showerhead region. • The mist-assisted FCE enhancement reached up to 26.2 % and 30.1 % at the PS and SS. Numerical simulations of mist-assisted showerhead (SH) steam film cooling on the vane’s leading-edge region of a hydrogen gas turbine have been performed under elevated operating conditions. Six rows of cylindrical film cooling holes were arranged staggered in a collinear counterflow layout. The steady Reynolds-averaged Navier-Stokes (RANS) approach in combination with the k-ω Shear Stress Transport (SST) turbulence model and a phase-coupling Lagrangian stochastic trajectory model was used to predict the mist/steam two-phase turbulent flow and film cooling performance, as well as the droplet dynamics in a cascade. The effect of mist concentration ( m s ) and droplet size ( d p ) with uniform and nonuniform distributions, for a range of blowing ratios (BR) from 0.5 to 2.0, on the mist-assisted steam film cooling effectiveness (FCE) on the showerhead region, pressure side (PS), and suction side (SS) of the vane was examined. Results for air coolant were also presented for comparison. It was found that steam provided higher FCE than air coolant, and the addition of mist could further enhance film coverage. With increasing m s , the FCE significantly increased on the vane PS and SS, especially at high BR, where the maximum FCE enhancement ratio reached approximately 26.2 % and 30.1 % at m s = 15 %, respectively. However, in the SH region, the mist proportion yielded a slight effect, and the best mist/steam FCE was obtained at BR = 0.5, independent of m s due to coolant lift-off. The effect of droplet size on FCE enhancement was closely related to the BR. The highest FCE enhancement ratio at the SH region was approximately 24 % at d p = 10 μm and BR = 2.0 due to mist evaporation. Furthermore, cases with uniform and nonuniform distributions of droplet size exhibited nearly identical film cooling on the vane surface, while significant differences in droplet trajectories were observed, particularly in the SS region.