Influence physics of mainstream pressure gradient on film hole discharge coefficient

Film hole discharge coefficients at different mainstream pressure gradients (zero pressure gradient, positive pressure gradient and negative pressure gradient) were tested, and influence physics of mainstream pressure gradient on film hole discharge coefficient was analyzed. Result shows that the maximum amplitude of effect on film hole discharge coefficient of mainstream positive and negative pressure gradients are 22% and 26% respectively. At different mainstream pressure gradients, bending effect and crushing effect of mainstream on jet are different, together with the changed interaction of jet with mainstream, and therefore the film hole discharge coefficient will be different. Crushing effect makes jet narrower and enhances the jet flow loss. Bending effect can change jet flow track; the positive pressure gradient makes jet flow close to the wall but far away from the free ejection direction, resulting in more flow loss; to the contrary, the negative pressure gradient may decrease the flow loss. The mixing effect enhances the momentum dissipation of jet, while at positive pressure gradient, the mixing effect is restrained and then momentum dissipation of jet decreases, however, the rule is opposite at negative pressure gradient.