Pressure measurements on a model delta wing undergoing oscillatory deformation

Abstract

Certain effects of leading-edge vortices on the surface pressures over a delta wing undergoing oscillatory deformation were investigated in a low-speed wind tunnel. The model, consisting of a sharp-edged delta plate, could be deformed in a particular mode of chordwise bending over its forward portion only; the deformation could be applied either as a static condition or as a continuous variation in the form of a sinusoidal oscillation. Surface pressures across the span were measured at two chordwise stations on the stationary part of the wing, the model being set throughout at a mean incidence of 5 degrees to ensure the presence of moderately strong vortices. The range of parameter variation was sufficient for the measurements to show the separate effects of frequency parameter and amplitude of deformation. Spanwise distributions of Fourier harmonic components derived from the measured oscillatory pressure changes were examined in relation to the behaviour of the vortices; non-linearities are present in the relationship between pressure change and deformation, and analysis of the results indicates the magnitude of the harmonics above the fundamental that are present in the pressure variations at spanwise positions close beneath a vortex. The fundamental components of the pressure variations are compared with the results of calculations based on lifting-surface theory. Within the limitations of the experiments (pressure measured only downstream of deformation) an empirical relationship involving a convective time-delay has been established between the unsteady pressures for an oscillatory deformation and the steady pressures for static deformations; the experimental conclusions are examined in relation to slender-wing theory, and more general implications of the results of the experiment are discussed.