Unsteady Aerodynamic Characteristics of Oscillating Cascades With Tip Clearance : 1st Report, Experiment

Abstract

An experimental study was conducted for revealing unsteady aerodynamic characteristics of oscillating linear cascades with tip clearance. To obtain aerodynamic forces acting on blades, the surface pressure was measured in both the chordwise and spanwise directions. To evaluate the unsteady aerodynamic forces due to oscillations of arbitrary inter-blade phase angle, the method of influence coefficients was adopted. Tip clearances were changed from 0.056% to 2.8% of the blade span. The aerodynamic blade loading was also changed. Results show that the tip clearance has a strong influence on the distribution of unsteady aerodynamic forces along the blade span. When tip clearance exists, aerodynamic damping forces decrease considerably over a large portion of the blade span. On the contrary, when the steady aerodynamic loading acts on blades, the influence of tip clearance is suppressed. The tip vortex increases the absolute value of the unsteady aerodynamic force in the region near the blade tip.