The Unsteady Response of a Blade Row From Measurements of the Time-Mean Total Pressure

An experimental procedure is described which permits the unsteady response of a rotating blade row to spatial variations in its inlet flow to be determined from measurements of the time-mean total pressure. This procedure has been employed to determine the unsteady circulation of a non-lifting rotor as a function of reduced frequency for two values of space-chord ratio. Comparisons of these experimental data are made with a recent theoretical analysis of the indirect or design problem of unsteady lift in a moving two-dimensional cascade. Both the experimental and theoretical data are shown to exhibit the same trends with variations in space-chord ratio and reduced frequency. These results demonstrate that the unsteady blade interference effects are significant, and that the representation of the unsteady response of a turbomachine blade row as an isolated airfoil is not valid for reduced frequencies less than 1.2.