Improvement of Ultra-High Lift Low-Pressure Turbine Blade Aerodynamic Performance Based on Evolutional Optimization Technique

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This study dealt with experimental and numerical studies on the flow field around a low-pressure linear turbine cascade whose solidity was changeable. The purpose of them was to clarify the effect of incoming wakes upon the aerodynamic loss of the cascade that wasaccompanied with separation on the airfoil suction surface, in particular for low Reynolds number conditions and/or low solidity conditions. Cylindrical bars on the timing belts worked as wake generator to emulate wakes that impacted the cascade. Pneumatic probe measurement was made to obtain total pressure loss distributions downstream of the cascade. Hot-wire probe measurement was also conducted over the airfoil suction surface. Besides, LES-based numerical simulation was executed to deepen the understanding of the interaction of the incoming wakes with the boundary layer containing separation bubble.This study also developed a new RANS-based method for predicting bypass transition of the boundary layer using intermittency t … More ransport equation. The base program was based on the boundary-layer analysis code given by Schmidt and Patankar (1988), implemented with Myong-Kasagi k -e turbulence model. The intermittency transport equation proposed in this study was the modification of Cho and Chung model (1992) with respect to the diffusion term and empirical model constants. The intermittent behavior of the transitional flow was invoked in the computation when the momentum-thickness based Reynolds number exceeded a criterion given by the empirical correlation of Abu-Ghannam and Shaw (1980). The method proposed in this study was applied to the prediction of boundary layer transition under the influence of free stream turbulence and pressure gradient. Through the comparison of the calculated results with the corresponding experimental data, for example ERCOFTAC T3A, the proposed method was proved to have a potential as a predictive tool of FST (free stream turbulence intensity)-induced boundary layer transition.This study lastly carried out LES investigation, along with measurements, on the interaction between inlet free stream turbulence and boundary layers with separation bubble over ultra-high lift low-pressure turbine airfoils. The cross section of the test airfoils is typical for highly-loaded LP turbines for civil aeroengines. The solidity of the cascade can be reduced by increasing the airfoil pitch by at least 25%, while maintaining the throat in the blade-to-blade passage. Reynolds number examined is 57,000, based on chord length and averaged exit velocity. Free-stream turbulence is about 0.85% (no grid condition) and 2.1% (with grid condition). Hot-wire probe measurements of the boundary layer are carried out to obtain time-averaged and time-resolved characteristics of the boundary layers under the influence of the freestream turbulence. A newly developed probe positioning tool, which is installed downstream of the cascade with minimal blockage, enables precise probe positioning along lines normal to the airfoil surface. Numerical analysis based on high-resolution LES (Large-Eddy Simulation) is executed to enhance the understanding of the flow field around the Ultra-High Lift and High Lift LP turbine airfoils. Emphasis is placed on the relationship of inherent instability of the shear layer of the separation bubble and the free-stream turbulence. Standard Smagorinsky model is employed for subgrid scale modeling. The flow solver used is an in-house code that was originally developed by one of the authors as FVM (Finite Volume Method)-based fully implicit and time-accurate Reynolds-Averaged Navier-Stokes code. Homogeneous isotropic turbulence created with SNGR (Stochastic Noise Generation and Radiation) method using von Karman-Pao turbulent energy spectrum is applied in the present study for the emulation of inlet turbulence. Less