Unsteady Wake Measurements of Airfoils and Cascades

In the prediction methods of unsteady response of airfoils and cascades, viscous effects are neglected and the steady-state, trailing-edge Kutta condition has been assumed, although not verified as an acceptable assumption. An investigation has been undertaken to study the unsteady characteristics of airfoils and cascades at lowfrequency parameters wherein the unsteady pressures, boundary layers, and wakes were measured in the presence of a sinusoidally varying gust flow. This paper presents mainly the time-mean and time-dependent Wake profiles and comparisons of the wake losses obtained from the unsteady and time mean wake profiles. The chordwise unsteady pressure differentials are also presented with results showing that the differential approaches zero at the trailing edge. The experimental unsteady pressure distribution on an airfoil is also compared with the predicted distributions. The amplitudes of the unsteady pressures show good agreement except in the trailingedge region; however, the agreement of the phase angle is poor. In the light of further studies, certain errors were observed in sectional unsteady lift and phase values presented in an earlier report. These values were recitified, and the corrected results are presented in this paper