THEORETICAL-STUDY ON THE UNSTEADY AERODYNAMIC CHARACTERISTICS OF AN OSCILLATING CASCADE WITH TIP CLEARANCE (IN THE CASE OF LOADED CASCADE)

In this paper, the analytical method developed previously for oscillating cascades was refined to deal with cascades with steady aerodynamic loading. The unsteady aerodynamic force acting on the linear oscillating cascades with tip clearance was calculated numerically by means of a vortex lattice method. Tip vortices were assumed to consist of linear vortex segments, and their paths were determined on the basis of experimental results measured using a 5-hole Pitot tube. The calculated damping forces showed good agreement with the corresponding experimental data. The effect of tip clearances on the flutter boundary was also investigated, and it was revealed that the cascade flutter was suppressed owing to the presence of tip clearances. When the blade oscillation was destabilized, it was found that the unsteady aerodynamic force became the exciting force at the blade-tip side sooner than at the hub side.