An experimental study of the effects on the low-speed aerodynamic characteristics of a strake-like fillet is described, modelled on one used on an Airbus A320 variant fitted at the leading edge of a swept wing-plate junction. The wing, swept back at 20°, was of NACA 0015 section and chord 500 mm, both normal to its leading edge. A turbulent boundary layer had developed on the plate well ahead of the junction. The tests were conducted at a unit Reynolds number of 1.56 x 106 m-1.

Surface pressure distributions were measured on the plate in the neighbourhood of the leading edge junction and also on the aerofoil and fillet at wing incidences of 0°, 3°, 6°, 9° and 12°. These were supplemented by surface oil-flow studies.

The mean velocity and turbulence intensity fields around the leading edge were examined for incidences of 0° and 9°, using both a single tube yaw meter developed for the purpose and an X-wire anemometer. The X-wire anemometer was also used downstream of the trailing edge of the swept wing; five of the Reynolds stresses and the mean velocity field were measured.

The sectional lift coefficients on the aerofoil were found to diminish as the junction was approached, slightly more so with the fillet than without it. The sectional drag coefficients due to pressure increased as the junction was approached, the fillet moderating this increase to only a small extent.

However, the addition of the drooped fillet modified the flow considerably. The horseshoe-like vortex was less well defined than without it. At zero incidence, the peak in the turbulence intensity levels was virtually eliminated on what became effectively the compression side of the wing due to the local camber introduced by the asymmetric fillet. The turbulence levels were also reduced by the addition of the fillet at an incidence of 9°. However, the turbulent activity was spread through a larger proportion of the viscous region. The secondary flows and the turbulence activity in the wake are associated with unrecoverable kinetic energy and will be manifest as drag on the surfaces forming the junction.

It is concluded that a carefully designed fillet, optimised for the cruise incidence of an aircraft, can reduce the peak turbulence levels in the junction. It remains unclear whether the total drag associated with the junction flow can be reduced significantly.

However because of its effects on the turbulence, there may be other benefits, for example on the efficiency of downstream elements, such as fuselage-mounted engine intakes or the following stages of an axial flow machine. Junction fillets might also be used to control the scouring of river beds around bridge piers.

The paper presents a method for the prediction of mean flow data (i.e. skin friction, velocity profile and shape parameter) for adiabatic two-dimensional compressible turbulent boundary layers at zero pressure gradient. The transformed law of the wall, law of the wake, the van Driest model for the complete inner region and a correlation between the Reynolds number based on the boundary layer integral length scale (ReΔ*.) and the Reynolds number based on the boundary layer momentum thickness (Reθw) were used to predict the mean flow quantities. The results for skin friction coefficient show good agreement with a number of existing theories including the van Driest II and the Huang et al. Comparison with a large number of experimental data suggests that at least for transonic and supersonic flows, the velocity profile as described by van Driest and Coles is Reynolds number dependent and should not be presumed universal. Extra information or perhaps a better physical approach to the formulation of the mean structure of compressible turbulent boundary layers even in zero pressure gradient and adiabatic condition, is required in order to achieve complete (physical and mathematical) convergence when it is applied in any prediction methods.

A method of determination of the wing lift-to-drag ratio of a propelled hang-glider in steady, level flight is described. The method requires a relatively small number of flight parameters to be measured. These measurements have been reduced successfully to the tilt angle of the propelling “trike”, i.e. a closed, wheeled, cabin hanging under the wing, and to the force on the flying controls only. The recording of these parameters and actual flight speed and altitude is sufficient to determine, after simple processing, the experimental speed and drag polars of the wing. The method is useful, in particular, for flexible wing research and development and allows quick aerodynamic tests.

Steady state aerofoil ground effect is studied both numerically and analytically. Discrete vortex and linear vortex panel methods are applied to a parabolic arc and symmetric Joukowski aerofoil, respectively. A single vortex model for the flow over the parabolic arc aerofoil is developed. The single vortex model and other analytical solutions, valid either near or far from the ground, are compared with the numerical results. The numerical results are used to delineate the influences of angle of attack, camber and thickness. For small values of camber and angle of attack, normalised lift is enhanced near the ground and reduced far from it. For a fixed distance above the ground, normalised lift decreases with increasing angle of attack and camber. Thickness reduces lift at all heights above the ground.

Two-dimensional potential flow expressed by means of the complex potential function uses Euler coordinates, i.e. a fixed point approach. However, there are many cases where the identical particle time is required, for example the settling time of suspended particles, heat convection (because in incompressible potential flow the heat and flow equations are uncoupled), and dispersion of fluid particles due to distortion.

In real variables the differential equation for the Lagrange time is generally too complicated because it involves two coordinates as functions of time. In the following a differential equation of single complex variable is derived.