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Languages : en
Pages : 30
Book Description
The objective of this project was to initiate investigation of film cooling flow control in order to improve its performance through active excitation of the film-cooling jet. A theoretical analysis was conducted and mechanisms that can play a defining role in film cooling control were identified on the basis of fundamental fluid-dynamics, prior experiments and preliminary numerical simulations. A cold flow wind-tunnel experiment incorporating a scaled-up, single film-cooling jet on a flat wall with a 90 deg injection angle was designed and built. The theoretical analysis was used to identify a window of essential flow-modulation parameters (frequency, duty cycle, mean blowing ratio, blowing ratio amplitude) within which film-cooling flow performance is expected to improve. A flow-pulsing system was designed, built and dynamically characterized. Both the wind tunnel boundary layer and jet exit flows were characterized using constant temperature anemometry. A series of preliminary experiments were conducted using reactive, Mie-scattering, laser-sheet visualizations for three mean blowing ratios with nearly zero low blowing ratio in the cycle, two duty cycles and four pulsing frequencies. The visualization results indicate that for the transverse jet with 90 deg injection angle, low frequency pulsations of the jet flow tend to increase the lateral coverage of the jet relative to the benchmark steady case without causing substantial lift-off at a blowing ratio of 0.5 and duty cycle of 50%. The observations are encouraging as to the feasibility of controlling the film cooling jet through mass flow pulsation and are consistent with predictions from fundamental analysis in terms of anticipated favorable operating conditions.
