Measurements have been made of the surface pressuredistributions in the region of the junction betweenan untapered wing, of NACA 0015 section swept backat 20°, and a flat plate on which a turbulentboundary layer had developed, for several values ofwing incidence. It is shown that the section liftcoefficient of the wing diminishes, while thepressure drag coefficient increases, as the junctionis approached. Oil-flow visualisations on the platesurface show the passage of the horseshoe-likevortex which forms when the retarded boundary layerflow separates as it approaches the leading-edge ofthe junction. Kinks in the isobars on the platecorrelate with the trailing “legs” of this vortex.The surface flow visualisations also show that theturbulence in the junction region spreads onto thewing from the leading edge at an angle of about10°.
A rotatable X-wire anemometer was used to makemeasurements of the mean velocity field and of fivecomponents of the Reynolds stress tensor, in thewake of the junction, with the wing at incidences of0° and 9°. Log-law (Clauser) plots were used withthe profiles Ū(Y) of longitudinalvelocity to estimate the skin friction coefficienton the plate, though adjustments of the zero forY were necessary to obtain asensible fit. These corrections were often largerthan can be readily explained, but the skin-frictionvalues are consistent with the corresponding,measured velocity correlation,
. The Reynolds stresses inthe wake region clearly show that the horseshoe-likevortex legs persist beyond the trailing-edge of thewing, the turbulence intensity being larger on thesuction side for the wing at incidence.
Average values of the skin-friction coefficient on theplate in the junction region are little differentfrom those away from the junction. No correspondinginformation is available for the skin-friction onthe wing, but if this is likewise unaffected by thejunction, then the total drag of the junction regionwill be greater than the sum of those of theisolated parts, simply because of the increase inpressure drag.