Simultaneous Heat Flux and Velocity Measurements in a Transonic Turbine Cascade

The gas turbine engine combustor generates turbulence that increases heat transfer on downstream turbine blades, but the mechanisms of that heat transfer are not fully understood. In this work, simultaneous time-resolved surface heat flux and velocity measurements have been made at three locations on the pressure surface of a high-turning transonic airfoil. Grids were used upstream of the linear turbine cascade to produce free-stream turbulence with two different inlet length scales, but the same turbulence intensity. High-frequency response instrumentation was used to obtain both steady and unsteady measurements. Results show that the time-averaged heat transfer is larger for the flow with the smaller integral length scale. Frequency-domain analysis demonstrates coherence between the fluctuations of heat flux and velocity over a broad range of frequencies. This is a direct indication that free-stream turbulent eddies penetrate completely through the boundary layer to the surface.