On The Flow And Heat Transfer Mechanism And Design Verification For High Efficiency Cooling Structures In The Turbine Trailing Regions

The cooling technology of hot-end components for the turbine is one of the bottleneck technology,which restricts the development of aero-engine industry in China.Due to the limitation of aerodynamic,structure and strength,the temperature is high,and the cracks,fracture and ablation are easily formed in the trailing edge area of gas turbine.In order to meet the cooling requirements of the fifth generation Aero-engine Turbine,the heat transfer capacity of trailing edge cooling structure should be further strengthened.Based on the above reasons,This paper studies the heat transfer in pin fin duct,latticework duct and cutback film cooling according to the idea of prototype research-strengthening mechanism research-coupled heat transfer simulation verification.In this paper,a gap is introduced to enhance the heat transfer in a pin fin duct.The interaction between the leakage flow and the wake/horseshoe vortex for the flow structure and heat transfer are revealed.The influence of the gap size on the flow field and heat transfer is studied botn in the static and rotating condition.The longitudinal secondary flow,which is drived from the pressure side to the suction side,is found at the pin fin wake region.These results show that the smaller clearance can increase the heat transfer of the pin fin duct and is helpful to protect the trailing edge of the turbine blade.Then,the dimple/protrusion is used to enhance the heat transfer and reveale the relationsip between the horeshoe vortex and longitudinal vortex.The results show that dimple/protrusion located behind pin fin is helpful for the heat transfer enahcnement.The pin fin channel is widely used in the aeroengine of European and American system.However,the Soviet Union / Russia prefers to use the latticework to enhance the heat transfer at the trailing edge.However,the research on the latticework channel is still in the initial stage.Therefore,the flow and heat transfer characteristics in the latticework channel are analyzed firstly,and the flow modes of the turn-spiral upward-impingement and bypass-spiral tube flow are proposed.In general,the turn flow results in low heat transfer enhancement and the impingement flow results in high heat transfer enhancement in the latticework.At the same time,the pressure loss in the latticework is larger due to the turn-impingement flow.Based on the above research,a method of reducing the channel resistance loss by using the detached latticework is proposed.The results show that the addition of gap greatly reduces the channel resistance,while the heat transfer coefficient decreases slightly.In addition,the method of heat transfer enhancement with truncated rib is proposed.The results show that the heat transfer coefficient increases significantly when the truncation position is in the turning region.Finally,the heat transfer characteristics of the staggered rib channel with jet cooling structure are analyzed.The results show that the location of the impact hole has a significant effect on the heat transfer for the jet cooling structure and latticeowork duct.Both the pin fin and the latticework belong to the internal cooling structure of the trailing edge,and the film cooling in the trailing edge area is also one of the important ways to protect the trailing edge area.Then,the effects of different cold air incidence angles,different lip shapes and different land shapes on the flow and heat transfer in the trailing edge half slit region are investigated.The results show that the separation vortex near the lip is the main flow structure in the cutback region,which has a significant influence on the film cooling efficiency distribution.When the incidence angle of the cold air is small,a large recirculation zone will be generated,and the recirculation area will gradually decrease when the incidence angle of the cold air increases gradually.Different lip shapes induce different separation vortices.When the lip shape is semicircular,the minimum separation vortex is beneficial to the downstream adiabatic film cooling efficiency.In general,the film cooling effect is poor when the cooling air flow velocity is small.The above research results are applied to an Aero-Engine Turbine to simulate the performance of different cooling structures under real working conditions.The results show that the surface temperature of turbine guide vane decreases by 17 k with concave dimple/ protrusion and 63 K with latticework.The results show that the surface temperature of rotor turbine blade decreases by 9K after adopting dimple/protrusion and 27 K by adopting latticework.The results show that the enhanced heat transfer method studied in this paper has great practical significance for reducing the turbine blade apparent temperature.