Reverse-oriented film cooling, which consists of film cooling holes oriented to inject coolant in the opposite direction of the freestream, is experimentally and numerically investigated. Tests are conducted at various blowing ratios (M = 0.25, 0.5, and 1.0) under both low and high freestream turbulence (Tu = 0.4% and 13%), with a density ratio near unity. The interesting flow field that results from the reverse jet-in-crossflow interaction is characterized using flow visualization, particle image velocimetry, and thermal field measurements. Heat transfer performance is evaluated with adiabatic film effectiveness and heat transfer coefficient measurements obtained using infrared thermography. Adiabatic effectiveness results show that reverse film cooling produces very uniform and total coverage downstream of the holes, with some reduction due to increased freestream turbulence. The reverse film cooling holes are evaluated against cylindrical holes in the conventional configuration, and were found to perform better in terms of average effectiveness and comparably in terms of net heat flux reduction, despite augmented heat transfer coefficient. Compared to shaped hole data from the current study as well as previous literature, the reverse film cooling holes generally exhibited worse heat transfer performance. The aerodynamic losses associated with the film cooling are characterized using total pressure measurements downstream of the holes. Losses from the reverse configuration were found to be higher when compared to cylindrical holes in the conventional and compound angle configurations. To investigate the unsteady three-dimensional flow physics, large eddy simulations were conducted to replicate the experiment at all three blowing ratios, under low and high freestream turbulence. The models were first validated against the experimental measurements, before being used to provide insight into the complicated flowfield associated with the interaction between the reverse film cooling jet and main crossflow. The specific in-hole velocity profile that arises within the short L/D hole was found to be closely tied to the nature of the resulting interaction, with different in-hole fluid regions playing specific roles. Additionally, the model was able to capture many of the coherent turbulent structures observed in the experimental flow visualization. A quasi-periodic shedding of the coolant fluid within the strong recirculation zone at the apex of the jet trajectory was identified. The cause of this phenomenon was found to be the migration of windward jet shear layer vortices to the leeward side, which disrupts the jet and subsequently the recirculation zone, allowing for the detachment of fluid in this region. Turbulent heat flux components from the large-eddy simulation were compared, with a discussion on the implications for use of isotropic turbulent diffusivity in RANS models. Insight gained from the experiments and numerical simulations was used to make notional suggestions of possible design improvements, to augment the beneficial aspects of the reverse configuration and mitigate some of the detrimental features of the design.
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