Numerical investigations of flow separation control for a low pressure turbine blade using steady and pulsed Vortex Generator Jets

This paper investigated numerically the application of Vortex Generator Jets (VGJs) to control flow separation on the suction side of a low pressure turbine blade. Firstly, numerical simulations of flow separation for a LPT blade, which based on Menter's SST k-ω turbulence model coupled with Langtry-Menter transition model, were performed for different Reynolds numbers Re∼100,000, 75,000, 50,000 and 25,000, for three freestream turbulence intensity (FSTI) of 0.08%, 2.35% and 6.0%. The pressure distributions around the turbine blade and streamline plots showing the flow separation were presented in this paper. Good agreement of the numerical and experimental results also showed the validity of the numerical scheme for simulating the flow separation occurring on a low pressure turbine blade. And then, steady Vortex Generator Jets (steady VGJs) having pitch angle of 30°, skew angle of 90°, blowing ratio of 2.0 were used to control the flow separation in the suction side of the low pressure turbine blade. Although steady VGJs have been illustrated to be extremely robust at suppressing low Reynolds number separation, the practical application of VGJs in the low pressure turbine engine is in the pulsed mode. The injection mass flow requirements of pulsed Vortex Generator Jets (pulsed VGJs) can be reduced drastically when similar flow control effect is obtained using steady VGJs. For pulsed VGJs, the pulse frequency has been found to be an important control parameter for the flow separation control. In this paper, cases with the duty cycle of 0.5 were studied for the pulse frequency ranging from 2.5Hz to 10Hz at Re=25,000 and freestream turbulence level of 0.08%. The numerical results showed that pulsed VGJs can effectively reduce and even eliminate the flow separation on the blade suction surface while there is an optimal pulse frequency. The flow control mechanism of VGJs on LPT blade was also revealed.