A study of jet exhaust-wing interaction

Abstract

Non-steady loading of surfaces embedded in a two-dimensional shear-layer is studied as a first step in understanding and predicting the forces generated in aircraft exhaust-jet and wing interactions. It is hypothesized that, for small separation distances between the jet and wing, coherent structures within the jet will cause non-steady lift forces. The coherent jet structures are approximated by those in a two dimensional shear-layer. A modified wind-tunnel has been used to produce a such a layer. A wing was inserted into this layer and the root mean square and power spectral density lift of the wing measured. In addition, a Vortex-Method based numerical model of the shear-layer and wing was used to provide predictions of the non-steady lift forces generated by the coherent structures. The experimental response of the wing at zero angle of attack was found to be self-similar and well behaved, with root mean square (rms) lift variations equivalent to a wing angle-of-attack, of 2.3°. The numerical calculations are found to be in qualitative agreement with the experimental data. While the model predicts the location and distribution of lift variation frequencies, it over-estimates the magnitude of the interaction by up to a factor of 4.