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 τ _w was observed just downstream of the groove for all three shapes. The increase in τ _w is followed by a small decrease in τ _w below the smooth-wall value before it relaxes back to the corresponding smooth-wall value at x / δ ₀≈3. At the higher R _θ , the maximum increase in τ _w 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 / U ₀, u ′/ U ₀ and v ′/ U ₀ 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 f _B ⁺ downstream of the different shaped grooves is similar to the τ _w distribution.