Quasi-Static Moment Measurements for Airfoils in an Annular Cascade

Abstract

Typical aerodynamic moment measurements are presented for airfoils in an annular cascade executing very slow pitching oscillations. Parameters which are varied are mean incidence, interblade phase angle, and amplitude of oscillation. The measurements take the form of a continuous loop of moment vs angular displacement. The characteristics of the experimental data are discussed and the need is pointed out for an analytical technique for converting the quasi-static data to dynamic moment loops for application to flutter prediction. Nomenclature flu, b n -Fourier coefficients b= airfoil semichord C M = moment coefficient, C M = Mj(2pW^2b 2 ) k -reduced frequency, k = a>bj W± M = aerodynamic moment / = time W± -relative approach velocity oci = mean incidence measured from W± to chordline a = interblade phase angle p = air density co = oscillation frequency 6 -angular displacement of airfoil 0o = amplitude of angular displacement s/c = space/chord ratio ft = stagger angle