| The aeroengine is the heart of the aircraft,and the performance of the engine largely depends on the temperature of the turbine inlet.In the case of limited temperature resistance of materials,the proposal of the new type of blade cooling structure of thin-double-walled blades is of great significance to the improvement of engine performance.In order to promote the application of thin-wall blade structures in engines,this paper studies the film cooling characteristics of basic film hole type(cylindrical hole,fan-shaped hole and forward inclined hole)with different length-diameter ratios based on numerical simulation,and optimizes the structure of the expansion holes;On the other hand,a conical combined hole is designed based on the construction concept of the heart shaped anti-vortex hole,and the film cooling and flow characteristics are analyzed to determine the optimal anti-vortex hole.The film cooling characteristics of the optimized anti-vortex hole and expansion hole at different positions of the blade are studied to determine the optimal film hole,and the Sellers model is verified to improve the prediction accuracy of film cooling effectiveness.The main research contents and conclusions of this paper are as follows:(1)Study on the influence of structure parameters of basic film hole on film cooling flow characteristics with different length-to-diameter ratios.The influence of structural parameters of compound angle film cooling holes,fan-shaped holes and forward inclined holes on the film cooling effectiveness is investigated under different blowing ratios and the length-to-diameter ratio of 2 and 5.The results show that when the length-to-diameter ratio is small,the jet flow in the film hole is not fully developed,resulting in greater momentum and turbulence at the film outlet,weaker film cooling performance.Fan-shaped holes have a good film cooling effectiveness under different length-to-diameter ratios.Both the lateral expansion angle and the forward inclination angle can reduce the jet flow and increase the film cooling effectiveness downstream of the holes.Both the lateral expansion angle and the forward inclination angle can reduce the jet momentum and increase the film cooling effectiveness downstream of the hole.When the length-to-diameter ratio is 2,the lateral expansion angle has better prominent effect on the film cooling effectiveness.On the basis of the above research,holes with different lateral expansion angles and forward inclination angles are designed,and the film cooling and flow characteristics are analyzed to determine the optimal hole structure.The results show that when AR is 2.48,the optimal hole with the lateral expansion angle of 18° and the forward inclination angle of 5° has the best film cooling performance.(2)Response surface analysis and structural optimization of the expansion hole with the short length-to-diameter ratio of 2.Based on the analysis of the film cooling effectiveness and flow characteristics of the basic film hole type,the response surface analysis of the expansion hole with the lateral expansion angle,the forward inclination angle and the length of the expansion section as parameters is carried out.The models of spanwise average film cooling effectiveness,the ratio of the area of the outlet and the inlet AR and the flow coefficient Cd with structural parameters are established,and the accuracy of the optimization results is verified.The results show that the cooling characteristics of the expansion hole are the best when AR=2.48.On this basis,nine kinds of expansion hole structures are designed based on the principle of fixed AR,and the downstream film cooling flow characteristics are analyzed.The results show that when the lateral expansion angle is 18° and the forward inclination angle is 5°,the expansion hole performs best cooling characteristic.(3)Research on the structure optimization of anti-vortex film cooling holes with short length-to-diameter ratio.Based on the construction concept of heart shaped hole,the lateral expansion angle and the forward inclination angle are introduced to design the conical combined hole.The film cooling and flow characteristic of the conical combined hole,heart shaped hole and the optimal expansion hole are investigated.The results show that the development of jet vortex downstream of the hole is closely related to the development of the flow characteristics in the hole.The lateral distance and height of the jet vortex is related to the vortex spacing in the hole and the distance between the vortex and the right wall in the hole,respectively.The lateral expansion of the conical combined hole makes the jet deviate along the span direction and to the front wall of the hole,which weakens the anti-kidney vortex in the downstream central area of film hole,and strengthens the single inward vortex on both sides.In general,the vortex structure downstream of the heart shaped hole is more advantageous than the conical combined hole in improving the jet adherence.When the blowing ratio is 0.5 and 1.0,the heart shaped hole has the highest spanwise average film cooling effectiveness.When the blowing ratio is 1.5,the hole of FH18/5 has better film cooling performance and the blowing ratio has little effect on it.(4)Research on the cooling characteristics of film holes at different positions of the blade.Based on the optimized film hole,the blade film cooling model is constructed,and the film cooling and flow characteristics of the heart shaped hole,FH18/5 expansion hole and compound angle hole at different positions of the blade are investigated.The results show that,compared with the composite angle cylindrical hole,the heart shaped hole and the FH18/5expansion hole perform better film adherence and wider film coverage.There is little difference in film cooling characteristics between the heart shaped hole and the FH18/5expansion hole downstream of the film hole on the pressure surface of the blade and the area of x/D<25 suction surface and.In the area of x/D<25 downstream of the film hole,the spanwise film cooling effectiveness of the FH18/5 hole is higher,and the difference between the two holes increase gradually with the increase of blowing ratio.(5)Research on the film cooling characteristics of blades with multiple rows of holes and optimization of the film cooling superposition prediction model of Sellers.The model of the multiple-rows holes on the suction surface and the pressure surface of the blade is constructed based on the research of the single exhaust hole of the blade,and the accuracy of film cooling effectiveness superposition prediction of Sellers model is analyzed.The results show the Sellers model has poor accuracy in predicting film cooling effectiveness at different positions of the blade for holes with short-length-diameter ratio.The influence of the jet of the front row of holes in the multiple-rows holes on the film distribution downstream of the rear rows of holes is analyzed,and the Sellers model for the suction surface and pressure surface of the blade is optimized,respectively.The average errors of the corrected film cooling effectiveness prediction model for pressure surface and suction surface are respectively 6.18% and 2.83%. |
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