The aerodynamic interaction at the junction between a forward-swept wing and a plate

Abstract

A study has been carried out of the aerodynamic interference flow arising at the junction of a cambered, swept-forward wing and a flat plate on which a fully-developed turbulent boundary layer approached the junction. CFD predictions of the pressure field in the junction region were carried out. Flow visualisation tests and surface pressure measurements over a wind-tunnel model were conducted at incidences from -3° to +9°. With the wing at zero incidence, a single-tube yawmeter was used to explore the flow around the leading edge of the junction arid an X-wire anemometer to examine the mean velocity and turbulence fields in the streamwise corners and at the trailing edge. The Reynolds number of the tests, based on the streamwise chord and a free-stream velocity of 30ms-1, was 1·03 x 106. At low incidence, a very weak separation occurred in the plate boundary layer, a very short distance upstream of the junction. However the oncoming stream converges into the junction, appearing to confine any vortical motion at the leading edge to within a very thin layer below the closest point of measurement to the plate. Rudimentary vortical flow developed slightly downstream of the leading edge, but dissipated further downstream. Although weak vortices were measured in the trailing-edge cross-flow plane, these were attributed to separations just upstream. The turbulence activity in the streamwise corners was found to be surprisingly low, especially on the compression side of the junction. Estimates of the skin-friction showed that it was lower over the majority of the trailing-edge crossplane than in the plate boundary layer upstream of the junction. At higher incidences, flow visualisations revealed severe stall in the junction, with large three-dimensional recirculating regions forming.