Abstract

Experimental and numerical investigations were conducted to study the effects of high blowing ratios and freestream turbulence on sweeping jet film cooling. Experiments were conducted on a nozzle guide vane suction surface in a low-speed linear cascade. Experiments were performed at blowing ratios of 0.5-3.5 and freestream turbulence of 0.6% and 14.3%. Infrared thermography was used to estimate the adiabatic cooling effectiveness. Thermal field and boundary layer measurement were conducted at a cross-plane (x/D = 12) downstream of the hole exit. Results showed that sweeping jet hole has a better cooling performance at high blowing ratios compared to a baseline 777-shaped. The Thermal field data revealed that the coolant separates from the surface at high blowing ratios for the 777-shaped hole but remains attached for the sweeping jet hole. Boundary layer measurement later confirmed that the oscillatory motion significantly lowers the momentum of a sweeping jet. Thus the coolant remains closer to the wall even at high blowing ratios. Large Eddy Simulations (LES) were performed for both sweeping jet and the 777-shaped hole to evaluate the jet interaction at the near hole regions. Results showed that 777-shaped hole has a strong jetting action at high blowing ratio that originates inside the hole breakout edges thus causing the jet to blow off from the surface. In contrast, the sweeping jet hole does not show this behavior due to its internal geometry and unsteady sweeping nature of the jet.

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