The response of a turbulent boundary layer to different shaped transverse grooves

The response of a turbulent boundary layer to three different shaped transverse grooves was investigated at two values of momentum thickness Reynolds numbers ( R θ=1000 and 3000). A 20-mm wide square, semicircular and triangular groove with depth to width ( d / w) ratio of unity was used. In general, the effects of the grooves are more significant at the higher R θ, with the most pronounced effects caused by the square groove. An increase in wall shear stress τw was observed just downstream of the groove for all three shapes. The increase in τw is followed by a small decrease in τw below the smooth-wall value before it relaxes back to the corresponding smooth-wall value at x / δ0≈3. At the higher R θ, the maximum increase in τw for the square groove is about 50% higher than for the semicircular groove and almost twice that for the triangular groove. The effect of the square groove on U / U0, u ′/ U0 and v ′/ U0 is much more significant than the effect of the semicircular and triangular grooves. There is an increase in the bursting frequency ( f B+) on the grooved-wall compared to the smooth-wall case. The distribution of fB+ downstream of the different shaped grooves is similar to the τw distribution.