Measurement of pitching-moment derivatives for aerofoils oscillating in two-dimensional supersonic flow

Abstract

Pitching-moment derivatives have been measured by a free oscillation technique on two-dimensional aerofoils of double wedge section with thickness/chord ratios of 0.08, 0.12 and 0.16; and on an aerofoil of single wedge section of thickness/chord ratio 0.16. The Mach number ranged between 1.37 and 2.43 and the axis position was varied over a wide range. The Reynolds numbers and the frequency parameters of the tests were less than 10power6 and 0.03 respectively. A few tests were made at incidence. For some axis positions and low values of Mach number, negative values of the aerodynamic damping were found considerably in excess of those predicted by theory. Theories which take into account thickness effects correctly predicted the trends of the derivatives with changes in axis position and in Mach number, and also the axis position at which the damping changes from positive to negative. However, substantial differences in the numerical values were often found, particularly at the low Mach numbers and these are attributed in part to the detached bow-wave on the thicker wings at low Mach numbers and in part to the effects of the boundary layer and of flow separations.