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The current study investigates the heat transfer and film-cooling effectiveness on a highly loaded turbine blade under steady and periodic unsteady wake induced flow conditions from both experimental and numerical simulation points of view. For the experimental measurements, the cascade facility in Turbomachinery Performance and Flow Research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engines. The current paper includes steady and unsteady inlet flow conditions. Moving wakes, originated from upstream stator blades, are simulated inside the cascade facility by moving rods in front of the blades. The flow coefficient is maintained at 0.8 and the incoming wakes have a reduced frequency of 3.18. For film-cooling effectiveness study a special blade was designed and inserted into the cascade facility that has a total of 617 holes distributed along 13 different rows on the blade surfaces. 6 rows cover the suction side, 6 other rows cover the pressure side and one last row feeds the leading edge. There are six coolant cavities inside the blade. Each cavity is connected to one row on either sides of the blade, except for the closest cavity to leading edge since it is connected to the leading edge row as well. The rows that are connected to the same cavity have identical injection hole numbers, arrangement (except for leading edge) and compound angles. Coolant is injected from either sides of the blade through the 6 cavities to form a uniform distribution along the lateral extent of the blade. In order to increase the effectiveness, the coolant injection holes are shaped holes. In the regions close to the end-walls of the cascade the holes have compound angles to overcome the effects of horseshoe and passage vortices. To study the film cooling effectiveness, the blade surfaces were covered with Pressure Sensitive Paint (PSP) excited with green light. Experiments were performed for Reynolds number of 150,000 and the average blowing ratio of coolant was maintained at one for all rows throughout the experiments. For heat transfer coefficient measurements, the liquid crystal method was used. For that reason the surfaces of the blade were covered by liquid crystal sheets and it was tested at the same Reynolds number. As computational platform, a RANS based solver was selected for this study. Sliding mesh technique was incorporated into the simulations to produce moving wakes. Experimental and numerical investigations were performed to determine the effect of flow separation, and pressure gradient on film-cooling effectiveness in the absence of wakes. Moreover, the effect of impinging wakes on the overall film coverage of blade surfaces and heat transfer coefficient was studied. Comparison of numerical and experimental results reveals deficiencies of numerical simulation.

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 Reynoldsaveraged 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.

The paper numerically and experimentally investigates the behavior of the boundary layer development and heat transfer along the suction and pressure surfaces of a highly loaded turbine blade with separation. To evaluate and compare the predictive capability of different numerical methods, Reynolds Averaged Navier-Stokes based solvers (RANS), Unsteady Reynolds Averaged Navier Stokes equation (URANS) as well as Large Eddy Simulation (LES) are used. The results of each individual numerical method are compared with the measurements. For this purpose, extensive boundary layer and heat transfer measurements were performed in the unsteady boundary layer cascade facility of the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. Aerodynamics experiments include measuring the onset of the boundary, its transition, separation and re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. Comparisons of the experimental and numerical results detail differences in predictive capabilities of the RANS based solvers and LES.

This paper describes the experimental investigations of film cooling effectiveness on a highly loaded low-pressure turbine blade under steady and periodic unsteady wake induced flow condition. The cascade facility in Turbomachinery Performance and Flow Research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engines. Moving wakes that are originated from upstream stator blades are simulated inside the cascade facility by moving rods in front of the blades. The flow coefficient is maintained at 0.8 and the incoming wakes have a reduced frequency of 3.18. There are a total of 617 holes on the blade, which are distributed along 13 different rows. 6 rows cover the suction side, 6 other rows cover the pressure side and one last row feeds the leading edge. Each row has a twin row on the other side of the blade with exact same number of holes and arrangement (except for leading edge). They both are connected to the same cavity. Coolant is injected from either sides of the blade through the 6 cavities to form a uniform distribution along the span of the blade. In order to study the film cooling effectiveness under periodic unsteady flow condition, the blade surfaces were covered with Pressure Sensitive Paint (PSP) and were excited with green light. Experiments were performed for Reynolds number of 150,000 and approximate blowing ratio of coolant was maintained at one, based on equal mass flux distribution, for all rows throughout the experiments. Experimental investigations were performed to determine the effect of flow separation, and pressure gradient on film-cooling effectiveness in the absence of wakes. Moreover, the effect of impinging wakes on the overall film coverage of blade surfaces was studied.