Velocity distribution in decelerating flow over rough surfaces

Abstract

An experimental program was undertaken to study turbulent boundary layers formed in decelerating open channel flows. The flows over a smooth surface and three rough surfaces were examined. Tests were conducted at a subcritical Froude number (~0.2) and varying depth Reynolds numbers (64 000 < Red < 88 000). The corresponding momentum thickness Reynolds numbers were small (1000 < Reθ < 2100). The velocity measurements were undertaken using a one-component laser-Doppler anemometer. Variables such as the shear velocity, the longitudinal mean velocity, Coles' wake parameter, and Clauser's shape parameter were examined. Three different methods for determining the friction velocity were investigated for use in sloping channels. The inner region of the boundary layer was found not to be influenced by the channel slope. The log-law slope and intercept were found to be the same as that noted for canonical boundary layers. The skin friction coefficient for the sloping smooth surface tests was found to be slightly higher than that noticed for flow over a horizontal surface. As indicated by the wake parameter, the free surface, the channel slope, and the roughness of the channel affected the outer region of the boundary layer.Key words: decelerating flow, open channel, log-law, friction velocity, power law.

One-dimensional bathymetry based on velocity measurements

“…Such noise level is realistic since Muste et al [7] have shown that the mean velocity can be measured within 3.5% in normal conditions and up to 10% in adverse (less visibility) conditions. Balachandar et al [27] have also demonstrated that the free-surface velocity can be measured within 2%. Similar analysis shows that the level of perturbation on the value of the velocity ratio () induces an error of comparable order of magnitude as the perturbed value in the reconstruction process.…”

Velocity Distributions in Grassed Channel

“…Similarly, El-Samman [3], studied velocity distribution using artificial vegetation and recommended that furthermore analysis is required to investigate the phenomenon of directing the flow towards the right side in a channel. Velocity distributions with fully developed, steady and uniform flows in open channels with roughed surfaces, have been reported extensively by several researchers [4][5][6][7][8].…”

Streamwise velocity distribution in irregular shaped channels having composite bed roughness

“…It is assumed that each element of the boundary influences the velocity of an arbitrary point in the channel section. Then, the total effect can be integrated along the boundary using the concept of line integral as u = boundary f (r).dP (2) where u is the streamwise velocity at a point in the channel section, f (r) is a velocity function similar to the conventional velocity profiles f (y), and dP is vector notation for a boundary element in the normal direction. In fact, function f in f (r ) and f (y) is unique.…”

“…It was placed at 4.8 m away from the beginning of the channel inlet. In this study, the roughness height (k s ) is taken as the median diameter, d 50 , for the two sand roughened surfaces [2]. In each case, data were collected for four aspect ratios of B/H = 4, 2, 1.33 and 1.…”

“…Velocity distributions with fully developed, steady and uniform flows in open channels and flow over rough surfaces, have been studied extensively by many researchers (e.g. [2][3][4][5][6]). There are well-known velocity distributions for openchannel flows, such as the power law and the Prandtl-Von Karman universal velocity distribution law.…”