Time-Resolved Analysis of the Base Region in Cooled Transonic Turbine Airfoils

High pressure turbine stages often work in the transonic regime. Hence the flow may be dominated by airfoil trailing edge shocks. In this paper, a detailed analysis of a test case representative of the trailing edge region of an airfoil is presented. The analysis has been performed reproducing the main characteristics of the flow field occurring at the blade trailing edge. The numerical campaign has been performed using the in-house HybFlow CFD code. Hybrid unstructured grids have been prepared for the selected configurations and special attention have been paid to the wake region discretization. The study started with the steady analysis with null and continuous blowing at several density ratios, on a round trailing edge representative of actual turbine blades. A main-flow Mach number of 1.5 have been initially considered to enhance the compressibility effects. The steady analyses allowed to evaluate the shock intensity variation increasing the coolant density ratio. Then, unsteady simulations have been conducted with both continuous and pulsating coolant at different frequencies. Frequency domain analyses have been performed and the results have been compared with each other. The obtained vortex structures have been also compared with the open literature results. Furthermore, shock intensity variations have been studied and their inclination monitored. For each frequency, the change in the shock intensity have been individuated and compared with the reference value obtained with continuous cooling. The results clarified the effect of continuous blowing on the flow field even far from the blade surface. Furthermore, uncommon vortex shedding structures have been individuated and discussed, depending on the coolant mass-flow rate.