Numerical Investigations On Cooling And Unsteady Flow Characteristics Of Turbine Blade Trailing Edge And Trenched Hole

In order to achieve higher thermal and propulsive efficiencies for aviation gas turbine engine,turbine inlet temperature is continuously raised over the years to the temperature far exceeding material limit.As a result,developing high-efficiency cooling technology for turbine component is of great significance to improve service life of turbine component and the overall level of design for the gas turbine.Turbine trailing edge(TE)cooling still remains a genuinely awkward problems because of rigorous geometrical and aerodynamic restrictions.Reasonable TE cooling design needs to provide sufficient protection to the blades within quite limited space of TE.At the present stage,pressure side cutback combined with internal pin-fins and film holes has been widely used in the current TE cooling designs.Unsteady vortex shedding process are generated in the flow field by the cutback structure,which ultimately determines the film cooling performance of the cutback surface.Meanwhile,the geometrical parameters of cutback and the outflow of upstream film holes change the cooling characteristics of cutback by influencing the vortex shedding process in the cutback region.Furthermore,it is crucial to solve the cooling design problems of turbine component by optimizing and designing new film hole structures.Trenched hole has long been favored by researchers in recent years because of maintaining higher film cooling effectiveness under larger blowing ratios.Recently,researchers attempt to apply the compound angle to the trenched holes,the combined configurations could obtain better cooling performance in theory.With the rapid development of the computing power,the numerical methods based on transient calculation,such as Large Eddy Simulation(LES)and Hybrid RANS/LES models,have been successfully applied to the numerical calculation of turbine components cooling.These methods not only provide more correct cooling predictions,but also precisely capture unsteady characteristics of the flow field.This shows that it is quite appropriate to apply these high-precision transient methods into the investigations about turbine blade TE cutback and trenched hole structures.Therefore in our paper,high-precision transient numerical methods were mainly adopted to investigate the cooling and unsteady characteristics of turbine blade TE and trenched holes in detail.The detailed work is carried out as follows:(1)Transient Scale Adaptive Simulation(SAS)method was adopted to explore and compare in detail the cooling and unsteady flow characteristics in the TE cutback region under low,medium and high blowing ratios,respectively.And the results were also compared with those obtained from steady calculations.It is found that,transient SAS method is capable of capturing and showing detailed unsteady flow characteristics,and provides accurate predictions of film cooling effectiveness under different blowing ratio conditions.However,the steady calculation only provides correct prediction tendency under the low blowing ratio,the results under medium and high blowing ratios are inconsistent with facts.(2)The effects of several representative TE geometrical parameters on cutback cooling are discussed,including cylindrical and elliptic pin fins,ejection lip shape and land structure.The influences of these geometric parameters variation on unsteady flow characteristics such as vortex shedding process in the cutback region are also investigated.(3)Pressure side cutback structure combined with upstream different types of film holes(cylindrical and fan-shaped film holes)is designed to explore the differences of cooling and unsteady flow characteristics under different blowing ratios.In addition,the effects of upstream cooling air ejected from film holes on the vortex shedding process in the cutback region are also analyzed to explain the changes of cooling performance fundamentally.The results show that adding upstream film holes significantly improves the overall cooling performance on the pressure side,and the fan-shaped film holes are more effective.The ejected cooling air from upstream film holes disturbs the development of B-R vortices and streamwise vortices in the cutback region.(4)Complete cooling structure designs are carried out in a realistic stator blade TE,the cooling structures mainly include pressure side cutback,internal pin-fins,centre joint and film holes.The flow and heat characteristics of the cooling designs under realistic high temperature and pressure conditions are investigated.The cooling and heat status on the blade surface are analyzed under different amount coolant by using adiabatic and conjugate heat transfer methods.(5)The trenched holes with backward compound angles(β=180° and 135°)and forward angle(β=0°)are designed.The cooling performance and unsteady flow characteristics are investigated by using high-precision LES method.The emphasis is on comparing the overall and lateral cooling performance of different trenched holes in the downstream region of the trench,and reveals the dominant vortex structures in and downstream of the trench.