On The Design Method And Heat Transfer Mechansim Of High Efficiency Cooling Structure In A Gas Turbine

The performance of gas turbine has direct effect on the safity and ecomony of the aircraft engine because turbine part is the key component of the aircraft core engine. The inlet temperature of gas turbine is increasing due to the pursuing of high thrust-weight ratio and high efficiency, which causes the urgent need of the aerodynamic and heat transfer development. In this study, the heat transfer mechansim and cooling structure design method of a high temperature turbine vane and blade in a high thrust-weight ratio aeroengine are focused on. A gas turbine cooling structure design platform and aero-thermal coupling optimization method is established by in-house code. The heat transfer and flow structrure characteristics on vane surface and endwall surface as well as typical cooling structrue element are numerical studied.A platform for high temperature gas turbine cooling structure design is established, which could design and evaluate a cooling structure quickly. Two gas turbine cooling structures are designed, i.e., one with film holes the other without film holes. The results show that this platform coud meet the requirement of cooling structure schematic design and it could also escape from the design blindness as well as increase the flexibility of the design. A method of aero-thermal coupling optimization which considers both the blade profile and cooling structure is developed. The objective function which takes the maximum temperature, average temperature, high temperature area, friction factor and aerodynamic efficiency is presented. The results show that the schemes with good heat transfer and aerodynamic performances could be achieved by using this method. The optimization efficiency is higher for vane and blade optimized separately than that in the whole stage optimization. It is also found that the gap between the reqirement of the cooling structure in next generation aircraft and current cooling structre is considerable large.The heat transfer characteristics of a typical gas turbine vane surface are studied. The results show that inlet Mach number has little effect on the vane transition. The increase of inlet turbulent intensity, turbulent scale and wall roughness causes the transtion occurrs in advance and change the pressure coefficient bump on suction side, indicating that the transition on suction side is transferred from separation induced transition to by pass transition. The bowed vane effect on the endwall flow structure and heat transfer characteristics in a typical gas turbine at different inlet flow angles is also studied. It is found that the bowed vane could affect the lateral secondary flow, and forces the vortex flows near the suction side at off design condiction,. It could reduce the vortex strength and decreases the endwall heat transfer. It is also found that the bowed vane moves the stagnation point to the pressure side and consequently reduces the endwall thermal load.In this study, the pin fin configurations effects on the heat transfer and friction factor characteristics in a Lamilloy cooling structure are also carried out. The results show that the pin fin arrangement changes the thermal perforamce mechanism. The optimal pin fin layout is concluded. In addition, the dimple is introduced in typical Lamilloy and double wall cooling structures. It is found that the adoption of dimple in both Lamilloy and double wall cooling increases the target surface heat transfer and reduces the outer wall temeratrue with small friction factor penalty. However, the dimple with big depth or diameter will reduces the target surface heat transfer dramaticly.The mechanism of dimple-pin fin effect in a wedge duct in high temperature gas turbine is also studied. The numerical results show that the use of dimple causes the flow impinge on the half dimple downstream in this wedge duct. The flow reattaches on the target surface as it flows out of the dimple. Then, it interactes with the vortex in the vinctity of pin fin leading edge and consequently increases the local heat transfer. Besides, the dimple which is arranged inline with the pin fin could both increases the heat transfer and recuces the friction factor by increasing the flow area. Then wedge duct convergence angle and dimple depth effect on the heat transfer characteristics are also studied. It is found that the optimal dimple depth in a large convergence angle is smaller than that in a small convergences algle. In this study, the dimple coufigurations with optimal thermal perforamnce are also concluded.