An investigation was conducted to explore the influence of density ratio and velocity ratio of mainstream/injectant upon the cooling effect of flat plane film using heat-mass transfer analogy.The injectant is air in the case of density ratio of 1.0

or heterogeneous gas in the case of density ratio of 1.5 and 2.0.The inclined angle between injectant and mainstream is 35° and the hole spacing is 3 times film hole diameter.The results indicate that

the spreading of injectant is controlled through the protected wall surface for a low velocity ratio

and controlled by convection for a high velocity ratio.With the increase of mass flux ratio

the transverse and longitudinal spreading could be expanded

thus increasing effectively the protective range;the reattachment point will move towards the downstream with the increase of momentum ratio under high velocity ratio.