Experimental And Numerical Investigation Of The Turbine Cascade With Film Cooling Jets

The performance of aero engine (thrust-to-weight ratio, specific fuel consumption) can be improved by increasing the turbine inlet temperature and the compressor pressure ratio. The turbine inlet temperature is now higher than the melting point of turbine material, cooling techniques such as film cooling must be applied to ensure the safety of turbine blade. At the same time, the characteristics of the flow and the aerodynamic performance of turbine cascade are affected greatly by the coolant ejected into turbine cascade from film holes. But there are only a few fundamental researches on this phenomenon in China. In this thesis, experiments and numerical simulations were carried out to investigate the effects of coolant injection on turbine cascade flow fields and the influences on aerodynamic performances.In a plane cascade, five holes pressure probe and boundary layer pressure probe were applied to obtained the detailed characteristics of the flow field when the cool-ant ejected from the film holes at leading edge, suction side and pressure side of tur-bine blade respectively. The velocity profile in boundary layer of blade and trailing flow are measured to study the effect of the coolant ejected positions, angles and mass flow rate. Then the rules of total pressure loss coefficient and energy loss coef-ficient varying with the coolant ejected positions, angles and flow rate were con-cluded.Experimental results show that the velocity profile in boundary layer of blade was changed because of the coolant component velocity in main flow direction. While the flow rate of coolant was larger, the flow loss was decreased when the coolant was ejected in smaller angle (smaller than 30°) from pressure and suction side. The flow loss was increased if coolant was ejected in large angle (larger than 60°) in all flow rate cases. When the coolant was ejected from the film holes in leading edge, the flow loss was always increased in all experimental cases. However, the rule of flow loss varying with the coolant ejected from trailing edge was very complicated.Numerical simulations were carried out additionally to investigate the detailed characteristics of internal flow in the turbine cascade. Shear-Stress-Transport model was used as the turbulence model and the outlet of film hole was set as the coolant inlet boundary in simulations. Mass flow rate, total temperature and ejection direction of coolant were defined in the coolant inlet boundary. Total pressure and static pres-sure of coolant were achieved in the coupled calculations with main flow.Horseshoe vortex induced by the component velocity in the vertical direction of main stream was found in numerical simulations and some part of main stream were transported into boundary layer according to this Horseshoe vortex. Annular turbine cascade was simulated furthermore based on the comparison among experimental and numerical results about the plane turbine cascade.Finally the flow loss according to the coolant ejected from trailing edge was calcu-lated using the Schobeiri model. Significant difference was appeared when comparing this result with experimental result.All the results demonstrate that numerical results gotten by three-dimensional cou-pled calculations agree with experimental results well. The affects of coolant ejection on the flow fields and aerodynamic performances of turbine cascade can be studied very well by the method applied in this study, which analyzes the experimental results achieved in plane turbine cascade together with the three-dimensional coupled nu-merical simulations.