TIP clearance influence on aerodynamic damping maps
This paper aims to investigate the influence of tip clearance on aerodynamic damping maps of an oscillating low pressure turbine (LPT) unshrouded blade row. Full-scale time-marching RANS CFD simulations in ANSYS CFX® v.16.2 employing models with 0%, 1%, 2% and 3% of span tip clearance are adopted. Tip clearance flow leads to a significant influence on the aerodynamic damping for blade torsion mode shape and least stable IBPA = 45°. No trend in local work coefficient are observed on the suction side, although increasing tip gap leads to a stabilizing trend on the pressure side. Aerodynamic damping maps are constructed for each tip gap. Torsion axes on the forward portion of the airfoil are found to be more stable than its aft counterparts. Bending dominated mode shapes are more stable in the cascade tangential direction. Finally, tip clearance leads to small changes in flutter characteristics for a few pitching axis locations.
