Effects of viscosity and density on film cooling effectiveness of turbine blade with pressure gradient and surface curvature

Film cooling represents a pivotal technology for the cooling of turbine blades. However, accurately predicting engine results at high temperatures and pressures based on laboratory results at room temperature and pressure is a challenging task. In the prediction process, matching the density ratio between the mainstream and coolant is the parameter of most interest to researchers. Despite this, the matching of the viscosity ratio is often overlooked, which may introduce bias and hinder the accurate prediction of film cooling effectiveness (η). In this study, four coolants were meticulously selected for experimentation in order to evaluate the effect of viscosity and density on η at various locations on the blade surface, which exhibit different curvatures and streamwise pressure gradients. Numerical simulation was employed to predict the mixing flow field of various viscosity coolants with the mainstream at different curvatures and streamwise pressure gradients. The results demonstrate that the increase of the density ratio increases η near the hole outlet and accelerates the decay of η along the flow direction. The effect of the viscosity ratio on η is not as obvious as that of the density ratio. When the viscosity ratio of the coolant increases from 0.5 to 1.5, η decreases by 0.05. The effect of viscosity on η is slightly affected by the change of the streamwise pressure gradient. However, the effect of viscosity on η is obviously different under different curvature conditions. The convex surface almost eliminates the effect of viscosity on η, while the concave surface enlarges the effect. On the blade, except for the gill area of the suction surface with a large convex curvature, the η of Ar with a larger viscosity is slightly lower than that of CO2.