1. The skin friction coefficient (Figure 10) is highest underneath the vortices and lowest outboard of the vortices (although measurements are probably unreliable in this region). The variations of skin friction coefficientbeneath the central, laterally diverging boundary layer are well predicted by the classic relation for a two-dimensional boundary layer in -0.25=e=o pressure gradient (Cf=0.0256Re, ). An analysis of these results, and measurements in other similar flows, indicates that divergence does not substantially alter the detailed structure of the boundary layer between vortex pairs with common flow downwards". Note that in both cases the Reynolds number based on momentum thickness is quite low in the central boundary layer, varying from about 2000 to about 500; however it &fully turbulent.
2. Experimental study of a turbulent horseshoe vortex using a three-component laser velocimeter
3. Longitudinal vortices imbedded in turbulent boundary layers