Study On Superposition Characteristics Of Film Cooling For Double-row Hole Injections

Film cooling is one of the most common and important cooling methods used in high-pressure turbine blades.Because of the special angle,the backward injection has the advantage of lateral coverage area compared with the traditional forward injection.In practice,the film cooling holes are mostly formed and discharged then it is necessary to study the film cooling effect used in the row.The effects of four combinations on film cooling efficiency and heat transfer coefficient were studied by numerical simulation.The combinations include forward and forward injection,backward and backward injection,forward and backward injection,backward and forward injection.The range of blowing ratio varies from 0.3 to 1.4.Results show that the circumfluence vortices at outlet of the backward hole strengthen the lateral spread of the injection,obviously.The larger the blowing ratio becomes,the more obvious the enhancement effect is.Spacing of rows is 12 times diameter of the film hole and the blowing ratio is 1.4.The lateral averaged film effectiveness combining forward and backward injections is increased by 17% to 233% depending on the different location.The lateral averaged film cooling effectiveness combining backward and backward injections is increased by 0 to 410%.The lateral averaged film cooling effectiveness combining backward and forward injections is increased by 16% to 70%.Results show that the heat transfer coefficient of each combination increases gradually with the increase of blowing ratio.The heat transfer coefficient of backward injection near the film hole is higher than that of the forward injection at all blowing ratios.When the forward injection is attached to the wall,the heat transfer coefficient is smaller,and increases when the injection begins to separate.When the blowing ratio is 1.4,the lateral average heat transfer enhancement coefficient of upstream forward injection is above 1.1,and the maximum is 1.35.In the downstream injection superposition region,the lateral average heat transfer enhancement coefficients combining backward and backward injections or forward injection and backward injections is above 1.2.Under the action of kidney-shaped vortices,the lateral average heat transfer enhancement coefficient in the direction of main flow is gradually higher than other combinations.The result is about 7% higher than the combination of backward and forward injection which is the lowest in most of the area.