Film cooling characteristics of cylindrical hole were measured using a transient liquid crystal measurement technique which can process nonuniform initial temperature.The influence of momentum flux ratio was tested.The results show that jets of large momentum ratio lift off from the wall after ejecting out and the cooling effectiveness in the upstream is very low.However

the area covered by jet and the effectiveness increase streamwise because the jets reattach the wall after lifting off

and moreover the cooling effectiveness in the region between adjacent holes is higher than that in the downstream hole centerline region.The cooling effectiveness distribution of small momentum ratio is just opposite to that of large momentum ratio.The normalized heat transfer coefficient distributions are similar for all momentum ratios in the downstream region.Heat transfer in the region between jets is stronger than the heat transfer in the hole centerline region because of the couple vortices.In the upstream region

a large and strong vortex is induced by the lifting off jet.And

a local region with high normalized heat transfer coefficient is formed due to this vortex.