LES Flow Control Simulations for Highly Loaded Low Pressure Turbine Airfoil (L1A) Using Pulsed Vortex Generator Jets

Seven different cases were examined experimentally and computationally to study LPT flow control using pulsed VGJs for the L1A airfoil. These cases represent a combination of variation in Reynolds number, Re (25,000, 50,000 and 100,000), based on the suction surface length and the nominal exit velocity from the cascade, blowing ratio, B (from 0.25 to 1), dimensionless frequency, F (from 0.035 to 0.56) and duty cycle, DC (10% and 50%). The data was obtained for the pressure distribution along the airfoil and downstream in the wake as well as for velocity profiles at six different stations downstream of the suction peak. The CFD was done with LES utilizing version 6.3.26 of the finite-volume code ANSYS Fluent. The CFD did provide further insight to better understand the physics of flow control. The comparison between CFD and experimental results for Cp, velocity profiles and Ψ_int is reasonable for all cases examined. Two of the cases examined did indicate that the higher DC could compensate for the lower F value. However, the effect of increasing the frequency appears to be stronger than increasing the DC value. The results from CFD using the Q-Criterion clearly illustrate how a separation bubble will persist at the lower frequency case (Case (2)) and the disturbances created from the jet flow do not have enough energy or time to travel further downstream to cause reattachment. On the other hand, the higher frequency case (Case (6)) did exhibit a penetration of the disturbance created by the jet into the separated region and caused reattachment, especially at the trailing edge. It appears that the jet was capable of breaking the large bubble into smaller ones with reattachment in between.