Research On Mechanism And Design Method Of Endwall Film Cooling Under Gas Turbine Aero-thermal Condition

In order to further improve the gas turbine efficiency,the turbine inlet temperature is increased while the coolant quantity is limited,which requires more efficient and fine cooling technique.Turbine endwall film cooling under complex interaction between secondary flows is one of the difficulties in cooling design.High level film cooling design criteria should be based on a comprehensive understanding of the film cooling mechanism and the aerothermodynamics in turbines.Based on the requirement of fine design of film cooling,this work investigates the mechanism of film cooling with cross flow and the aerothermodynamics of the turbine in complex conditions,developing the film cooling design method.The flow structure near the endwall is simplified and the cross flow is decoupled from the complex endwall environment to investigate the influences of the endwall cross flow on the film cooling performance.The endwall cross flow laterally migrates coolant in boundary layer from high pressure to low pressure regions,the deflection angle of coolant increases from the mainstream to the endwall.The cross flow forces coolant to laterally migrate and the deflection angle is in negative correlation to the momentum ratio of the cooling jet.The vortex structure of cooling jet is asymmetrical with cross flow and limits coolant to diffusing.However,The cross flow enhance the coolant diffusion,which increases the area averaged cooling effectiveness at high blowing ratio by 15%.Based on the cooling performance with cross flow,the characteristics and the mechanism of cooling jet superposition are investigated using the experimental method,that measures the adiabatic cooling effectiveness of each jet under the condition of double-row film cooling.The deflection characteristic of the cooling jets with cross flow and the relation position of the double-row cooling holes influence the relative position of the cooling traces,which dominates the interaction characteristics of double-row jets,such as blowing off coolant,vortices interaction and diffusion enhancement.A two-dimensional(2D)superposition method based on Sellers model is proposed in current work and the advantages of it are validated in experiment.Compared with the traditional 1D superposition method,this method can not only reduce the predicting error by more than 20%,but also accurately predict the 2D distribution of cooling effectiveness.Based on these advantages,a 2D design method of film cooling is proposed.According to the requirements of the 2D cooling design method,this work proposes a 2D parameterized method of adiabatic cooling effectiveness by the scalar transport model and the Taylor frozen hypothesis.This work investigates the local non-periodic influences caused by combustor-turbine mismatching.The non-uniform inlet condition dominates the temperature distribution of vanes and blades,and it leads to large area averaged temperature difference between neighboring vanes.The non-uniformity clocking positions dominate temperature difference between neighboring vanes and area averaged temperature of different rows,while the swirl orientation dominates the radial temperature distribution on vanes and blades.Based on the investigations and the results,this work improves the traditional design criteria and supports the fine design of film cooling under gas turbine complex aerothermal condition.