Analysis of the cooling performance of a cylindrical hole designed for the suction side of the LS89 vane under transitional conditions

The necessity to deal with even more demanding constraints on gas turbine emissions obliges the designers to cope with increasingly stringent operating conditions, thus leading to the adoption of high-fidelity predictive tools to evaluate the unsteady response of gas turbines components to various cooling technologies. Computational Fluid Dynamics has proved to be a reliable method for both the analysis of thermal loads and the design of cooling solutions for turbine stages. The unsteady interaction between main-flow and coolant is still an open topic that could lead to innovative strategies for the enhancement of the cooling effectiveness. In the present paper, CFD is used to analyse the unsteady performance of film cooling in a transonic high-pressure vane. The original test case is the LS89 vane, designed and experimentally investigated at the Von Karman Institute for Fluid Dynamics for several aero-thermal configurations. The MUR237 transonic configuration is selected as representative of highly loaded vanes without shocks. Given that this vane is originally uncooled, the cooling system is specifically designed for the present work, based on the non-dimensional geometrical and operating conditions of the high-pressure transonic MT1 cooled vane. A numerical campaign has been performed using the commercial software Star-CCM+. Turbulence is modelled through the k-ω SST model in conjunction with the γ-Reθ transition model, which is able to capture the transition of the boundary layer. The transition model constants are tuned to match the available experimental data for the LS89 original configuration, where natural transition occurs on the suction side. For the cooled vane, the areo-dynamic performance of the film cooling geometry is assessed for by means of the discharge coefficient at different pressure ratios. On the other hand, the thermal response is studied in terms of adiabatic effectiveness, heat transfer coefficient and Net Heat Flux Reduction distributions for all the investigated blowing ratios (in a range between 0.5 and 1.5). Eventually, the cold jet interaction with the hot flow is studied both in the vicinity of the cooling hole outlet section as well as in the far-field.