Flow over a Trailing Flap and Its Asymmetric Wake
Detailed measurements of pressure and velocity characteristics are reported for the attached flow on a trailing flap and in its downstream asymmetric wake. The results indicate that the flow over the flap is subjected to an adverse pressure gradient. Near the trailing edge, an inflection point develops in the streamwise velocity profile and the flow approaches intermittent separation. The wake is asymmetric with a destabilizing curvature on the suction side and a stabilizing curvature on the pressure side. Streamwise variations in the near wake are primarily confined to the inner layer, and further downstream the mean velocity and turbulence quantities attain selfsimilar profiles. Nonequilibrium effects are present in the near wake and imply that mixing length models are not appropriate. Both the pressure gradient term and the cross-stream gradient of the turbulent stresses are found to be important. Streamwise gradients of the turbulent stresses are, however, small. Nomenclature b = width of the upper part (y/d>0) of the wake B = constant in the law of the wall equation c = chord length (Fig. 1) cp — pressure coefficient cpw = pressure coefficient along the flap surface cpoo = freestream pressure coefficient k = constant in the law of the wall equation lp = distance from the wake center to the point where the streamwise velocity defect in the pressure side is half the maximum defect /5 = distance from the wake center to the point where the streamwise velocity defect in the suction side is half the maximum defect L = mixing length n = normal distance from the flap surface p = pressure q = kinetic energy of turbulence s = distance along the surface measured from the trip wire ii, u' = mean and fluctuating velocity in the streamwise __ direction u'v' — mean shear stress u'2 =mean normal stress in the streamwise direction uc = mean streamwise velocity at wake center iieu = mean streamwise velocity in the suction-side freestream uel = mean streamwise velocity in the pressure-side freestream Href = mean reference velocity in the streamwise direction v,v' = mean and fluctuating cross-stream velocity v'2 = mean normal stress in the cross-stream direction w'2 =mean normal stress in the spanwise direction Xty = streamwise coordinate in the wake measured from the trailing edge, and cross-stream coordinate <5 = boundary-layer thickness, i.e., the distance from the wall where the velocity reaches 99.5% of the freestream velocity