| The turbine shroud is located between the engine turbine casing and the turbine blade,which protects the engine casing from the erosion of the high temperature flow and reduces the leakage flow.The turbine shroud structure and the characteristics of nearby gas determine both the compound angle jet and the reverse jet air film cooling on the turbine shroud surface.The study of the film cooling angle is limited to the small angle of the gas hole or the reverse jet,and the jet cooling with large angle corresponding to the turbine shroud has not been reported.Study on film cooling characteristics of compound angle can provide data support for the design of turbine shroud cylindrical gas film cooling.In order to explore the influence of the cylindrical hole angles on film cooling characteristics,numerical simulation was carried out to investigate the film cooling effectiveness at jet angle of 15°,45°,75°and orientation angles of 0°,60°,120° and 180°respectively.The results show that in the three jet angles,the jet angle of 15°has the best film cooling efficiency and the spanning coverage area,and orientation angle of 60° structure has the highest spanwise averaged film cooling effectiveness.Under the three kinds of jet angles,The distribution of spanwise film cooling effectiveness is increased and film cooling effectiveness is improved in the structure of 180°orientation angle as the increase of blowing ratio.The distribution of spanwise film cooling effectiveness is decreased and film cooling effectiveness is reduced in the structure of 0°orientation angle as the increase of blowing ratio.When the jet angle is 75°,the orientation angle has little influence on the film cooling efficiency,the vortex structure is obvious,and the cold air is easily detached from the wall.The structure of the 180°orientation angle has the highest film cooling efficiency,and the difference is less than 10% between the three blowing ratios.In order to improve the turbine shroud film cooling efficiency,semi-elliptical shape slots is proposed on the basis of hole-groove structure.Numerical simulation was carried out to study the flow field,temperature field and film cooling effectiveness downstream of cylindrical holes with semi-elliptical shape slots to reveal the mechanism of film cooling combined cylindrical holes and semi-elliptical slots.Influences of the depths of the semi-elliptical shape slots on film cooling were analyzed at different blowing ratios.The results show that the semi-elliptical slots are more easily to form counter-rotating vortices and the spanwise averaged film cooling effectiveness of the semi-elliptical slot model is increased5%-119% compared with that of the saw tooth slot when the blowing ratio is 0.5 and 1.5.The distribution of spanwise film cooling effectiveness is more uniform and film cooling effectiveness is improved in the span regions between the cylindrical holes as the increase of the depths of semi-elliptical slot.At the blowing ratio of 0.5,the influence of the depths of thesemi-elliptical shape slots on spanwise averaged film cooling is less than 15%.At the blowing ratio of 1.5,the spanwise averaged film cooling effectiveness of the semi-elliptical slot depths of 0.5 times of film hole diameter case is higher than that of 0.25 and 0.75 times of film hole diameter by 55%~107% and 2%~16% respectively. |
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