Numerical Study on Effects of Density Ratio on Film Cooling Flow Structure and Film Cooling Effectiveness

Abstract

To understand film cooling flow fields on a gas turbine blade, this paper reports a series of large-eddy simulations of an inclined round jet issuing into a crossflow. Simulations were performed at constant momentum ratio conditions, IR = 0.25, 0.5, 1.0 and Reynolds number, Re = 15,300, based on the crossflow velocity and the film cooling hole diameter. Density ratio, DR, is changed from 1.0 to 2.0, and effects of the density ratio on vortical structures around the film cooling hole exit and film cooling effectiveness are investigated. The results showed that the vortical structure of the ejected jet drastically changes with varying density ratio. When the density ratio is comparatively small, hairpin vortices are formed downstream of the hole exit. On the contrary, when the density ratio is comparatively high, the formation of the hairpin vortices is suppressed and jet shear layer vortices are formed on side edges of the cooling jet. The jet shear layer vortices conveys the coolant air to the wall surface. As a result, higher film cooling effectiveness is obtained at comparatively high density ratio conditions compared to comparatively low density ratio conditions. Additional simulations were performed to discuss a possibility of an improvement in the film cooling effectiveness by controlling the formation of the jet shear layer vortices.