Effect of inverse blade angle slots on a transonic rotor performance and stability

Abstract

The aim of the paper is to explore the effects of inverse blade angle slots CT (IBSCT) on the NASA Rotor 67 stability and performance at 100% design speed. Considering the compromise between the stall margin improvement (SMI) and efficiency loss for the rotor, three kinds of IBSCT were design and researched in this investigation. The unsteady calculated results show that the slots with 100% axial coverage rate (IBSCT1), the slots with 100% axial coverage rate and 60 degrees radial skewed angle (IBSCT2) and the slots with 40% axial coverage rate and 60 degrees radial skewed angle (IBSCT3) can generate about 20.65% SMI with 0.766% peak efficiency loss (PEL), 24.28% SMI with 0.755% PEL and 17.61% SMI with −0.011% PEL respectively. Moreover, the flow field analyses show that the adverse flows made by the low energy tip clearance leakage flow (TLF) near the rotor tip leading edge passage play the key role in making the rotor with smooth wall stall, and the adverse flows are resulted from the interaction between the rotor tip passage shock wave and the TLF. When IBSCT1 was applied, the adverse flows were well restrained. However, the interaction between the passage mainstreams and the flows formed inside the slots makes extra flow losses, which make the rotor efficiency decrease at some operating points. Hence, the rotor stability was improved with the peak efficiency drop. Due to the deflection of some angle along the radial direction for the slots, IBSCT2 generates more useful injected flows inside the slots than IBSCT1. Due to the decrease of axial coverage rate for the slots, the injected flows formed inside the slots for IBSCT3 are less useful than those for IBSCT2 and IBSCT1, but IBSCT3 generates smaller flow losses in the rotor tip passage than IBSCT2 and IBSCT1.