Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows

Abstract

a b s t r a c tThe logarithmic layer of double-averaged (in time and space) streamwise velocity profiles obtained from field measurements made in the Swiss rivers, Venoge and Chamberonne is parameterized and discussed. Velocity measurements were made using a 3D Acoustic Doppler Velocity Profiler. Both riverbeds are hydraulically rough, composed of coarse gravel, with relative submergences (h/D 50 ) of 5.25 and 5.96, respectively. From the observations, the flow may be divided into three different layers: a roughness layer near the bed, an equivalent logarithmic layer and a surface or outer layer. It was found that a logarithmic law can describe the double-averaged profiles in the layer 0.30 < z/h < 0.75. The parameterization of the logarithmic law is discussed. Special emphasis is given to the geometric parameters roughness and zerodisplacement heights and to the equivalent von Karman constant.

Application of Displacement Height and Surface Roughness Length to Determination Boundary Layer Development Length over Stepped Spillway

“…In many instances of open-channel flow, it was found that a logarithmic law can describe the velocity profile in the bottom 15% of the flow depth [18], 20% [19], 50% [20] or 75% [13]. Thus there is not an explicit standard for the flow heights on the estimation of u*, d and z0 using a fitted logarithmic profile.…”

“…At the step edges, the vertical velocity distribution in the turbulent boundary layer can be approximated by a power law [8][9][10][11], and data obtained in bed-roughened flows show that there is a region above the roughness layer where the smooth boundary upstream of the steps still adequately describes the vertical velocity distribution [12][13][14]. This transition boundary layer will be used to investigate and characterize the roughness parameters and the development of turbulent boundary layer.…”

Momentum balance in flows over mobile granular beds: application of double-averaging methodology to DNS data

“…Finnigan, Shaw, & Patton, 2009;Raupach & Shaw, 1982). In recent years, it has also been successfully employed for studies of open-channel flows over fixed rough beds, examples of which are given in Nikora and Rowiński (2008), Franca, Ferreira, and Lemmin (2008), Mignot, Barthelemy, andHurther (2009), Ferreira, Ferreira, Ricardo, andFranca (2010), Yuan and Piomelli (2014). Among other findings, these studies highlight the potential importance of additional (dispersive) fluid stresses, which appear due to roughness effects that introduce local heterogeneities in the time-averaged flow.…”

Turbulence in Rivers

“…The analysis and modeling of heterogeneous and irregular-bounded open-channel flows by means of double-averaging (DA) methods is presented by several authors for different problems in fluvial hydraulics (Aberle and Koll 2004;Manes et al 2007;Franca et al 2008;Stoesser and Nikora 2008;Ferreira et al 2010, among others). Franca et al (2010) and Mignot et al (2009) Recently, a journal's special issue on the application of the double-averaging approach to rough-bed flows was published (cf.…”