Combined numerical and experimental investigations of heat transfer of a highly loaded low-pressure turbine blade under periodic inlet flow condition

Abstract

This paper experimentally and numerically investigates heat transfer characteristics of a low-pressure turbine blade under steady/unsteady flow conditions. Generally, the low-pressure turbine blades are not exposed to excessive temperatures that require detailed heat transfer predictions. In aircraft engines, they operate at low Re-numbers causing the inception of large separation bubbles on their suction surface. As documented in previous papers, the results of detailed aerodynamic simulations have shown significant discrepancies with experiments. It was the objective of the current investigation to determine the discrepancies between the experimental and numerical heat transfer results. It is shown that small errors in aero-calculation results in large deviations of heat transfer results. The characteristics of the blades mentioned above, make low-pressure turbine blades suitable candidates for evaluating the predictive capability of any numerical method. Documenting the scope of these discrepancies defines the framework of the current paper. The periodic flow inside the gas turbine engine was simulated using the cascade facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. In this study, the wakes that originate from stator blades were simulated by moving rods. The instrumented blade was covered with a liquid crystal sheet and it was used to measure heat transfer coefficient. Reynolds-averaged Navier–Stokes equations were used for numerical investigation purposes. Measurements and simulations were conducted at three different Reynolds numbers (110,000, 150,000, and 250,000). Furthermore, for unsteady flow condition, reduced frequencies of the incoming wakes were varied. The current paper includes a comprehensive heat transfer assessment of the predictive capability of Reynolds-averaged Navier–Stokes based tools. The effect of the separation bubbles on heat transfer is thoroughly discussed in this paper. Comparisons of the experimental and numerical results detail the differences and identify the sources of error that leads to in accurate calculations in terms of predicting heat transfer calculation results.