CONJUGATE MODELLING OF A FULLY FILM COOLED VANE AT TRANSONIC CONDITIONS

Internal and film hole cooling is widely used as a means to allow for higher turbine inlet temperatures while keeping blade metal temperatures within a tolerable range of the material. Appropriate modelling of the internal and external heat transfer is needed to understand and identify localized high temperature zones on the blade surface that could lead to premature failure. In order to accurately predict this, conjugate heat transfer modelling is used to solve for the coupled temperature fields of the solid and fluid. The modes of heat transfer include convection outside the vane surface, conduction through the vane material, and convection of the cooling flow inside the vane channels. The purpose of this study is to evaluate conjugate heat transfer predictions using commercially available computational fluid dynamics (CFD) software to model the internal and film cooling of a turbine vane operating from transonic to supersonic conditions. The boundary conditions of the conjugate models are based on recently obtained experimental data and the surface temperature predictions are compared to the experiments. Both Mach number and Reynolds number effects on surface temperature were evaluated at different blowing ratios in this study. The results from this work show that overall cooling effectiveness near the cooling holes increased with increasing blowing ratio despite the film cooling flow reaching blow-off conditions. Furthermore, the overall cooling effectiveness near the cooling holes increased slightly near the pressure side cooling holes with a higher exit Reynolds number in the mainstream flow, but not significantly elsewhere on the vane surface. However, a supersonic exit Mach number condition, which results in a fishtail shock that impinges on the suction side of the vane, yielded a sharp increase followed by a decrease in cooling effectiveness around the shock impingement.