Effect of a transverse square groove on a turbulent boundary layer

The effect of a transverse square groove on a turbulent boundary layer has been investigated at two values of momentum thickness Reynolds numbers (Rθ=1000and3000) using hot-wire anemometry. The ratio of the groove width to the boundary layer thickness (w/δ1) is approximately 0.07. The wall shear stress (τw) is estimated from the velocity profiles using the Clauser chart method and by assuming a power law velocity distribution. The smooth wall results indicate the Clauser chart is better suited at higher Rθ, whereas the power law is more suited at lower Rθ. The effect of the groove on τw at the lower Rθ is not significant. At the higher Rθ, there is a sudden increase in τw just downstream of the groove, followed by an undershoot and an oscillatory relaxation back to the smooth wall value. The mean velocity profiles (U+) are not affected by the presence of the groove at both Rθ. There is, however, a small reduction in the turbulence intensity in the near-wall region (y+≲10) at both Rθ. There is a strong correlation between the τw and wake parameter (π) distributions, with an increase in π for a decrease in τw. The growth of the internal layer immediately downstream of the groove is very rapid at both Rθ, followed by a much slower growth beyond x/w≳7.