A study of turbulence in open channel flow

Three series of experiments were conducted to study the effect of Reynolds number, near-wall perturbation and background turbulence on the characteristics of smooth open channel flows. Measurements were carried out using a laser Doppler anemometer. The variables of interest include the mean velocity, the turbulence intensity, probability density distribution and Gram-Charlier series coefficients. For the range of Reynolds number studied, the turbulence intensity profiles show that the effect of Reynolds number can be significant in open channel flows. However, the probability density distributions at various distances from the bed do not indicate any Reynolds number effects. The coefficients of the Gram-Charlier series expansion are nearly constant in overlap region and the region of nearly constant value of coefficients increase with increasing Reynolds number. The near­ wall perturbed velocity profiles indicate that the overlap region develops more slowly than the inner and outer regions. The mean velocity profile is recovered at the farthest downstream station, whereas the turbulence intensity and higher-order coefficients do not indicate complete recovery. The presence of higher background turbulence significantly alters the characteristics of flow. Velocity defect in the outer region is decreased resulting in more negative values of the wake parameter, while the GramCharlier series coefficients are more uniformly distributed through out the depth. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.