Response of a skewed turbulent boundary layer to favourable pressure gradient

Experimental results are reported for the response to a favourable pressure gradient of an initially turbulent boundary layer (Re _θ?≈?1600) developing on a flat plate with its leading edge skewed at 60° to the approach flow. The pressure gradient orthogonal to the leading edge is nominally the same as that which was shown by Escudier et?al. [(1998) Exp Fluids 25: 491–502] to cause extreme thinning of a two-dimensional (2D) (i.e. unskewed) turbulent boundary layer and the intermittency in the immediate vicinity of the surface to fall to zero, i.e. an apparent laminarisation of the boundary layer. In the case of the skewed boundary layer, the responses of the turbulence and mean-flow structures are qualitatively similar to those for the 2D situation. However, the streamwise pressure gradient is much weaker than for the 2D experiment and the extent of the changes it produces is much reduced. Even so, the changes are considerably greater than would be expected from the magnitude of the streamwise pressure gradient.