Linear Oscillating Cascade Unsteady Aerodynamic Experiments

Abstract

Experiments in a linear oscillating cascade reveal that the wind tunnel walls enclosing the cascade have, in some cases, a detrimental effect on the oscillating cascade aerodynamics. In a subsonic flow field, biconvex airfoils are driven simultaneously in harmonic, torsion-mode oscillations for a range of interblade phase angle values. It is found that the cascade dynamic periodicity — the airfoil-to-airfoil variation in the unsteady surface pressure coefficient, C p — is good for some values of interblade phase angle but poor for others. Calculations based upon linearized unsteady aerodynamic theory indicate that pressure waves reflected from the wind tunnel walls are responsible for the cases where there is poor periodicity in C p . However, the periodicity in the unsteady pressure difference coefficient ∆C p is generally good, apparently due to cancellation of acoustic modes imposed by the wind tunnel walls. The unsteady pressure difference coefficients are correlated with linearized analysis predictions.