Author(s): M. A. A. Faruque; Bushra Afzal; Ram Balachanda
Linked Author(s): Ram Balachandar
Keywords: No Keywords
Abstract: A series of experiments were conducted to study the effect of near-wall perturbation and the recovery of the flow on the characteristics of smooth open-channel flows. Measurements were carried out using a laser Doppler anemometer. The variables of interest include mean velocity, turbulence intensity, Reynolds shear stress, probability density function and Gram-Charlier series coefficients. The results indicate that the profiles downstream of near-wall perturbation are quite distorted. The mean velocity profile was similar to the reference profile at x/d = 60, however, the velocity defect profile does not show complete recovery in the overlap region. The near-wall perturbed flow indicates that the overlap region develops more slowly than the inner and outer regions. The streamwise turbulence intensity profile displayed two peaks downstream of the near-wall perturbation. The flow separation from the sphere reattaches to the bed and forms a mixing zone downstream. This is indicated by a region of very high turbulence and the two peaks (near-wall peak and mixing zone peak) are perhaps located very close to each other at x/d = 10. Due to the spreading of the mixing zone, at subsequent stations, the location of the peak moves away from the wall, while the magnitude of the peak decreases. The perturbed flow measurement indicate an increase in shear stress values in the near wall region.
Year: 2009