Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

Abstract

The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the nonuniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant j and to estimate sets of log-law integration constant B r and wake parameter G, where their findings are also compared with values from previous studies. From j, B r and G findings, it has been found that the log-wake law can sufficiently represent the nonuniform flow in its non-modified form, and all j, B r and G follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter b equations. Their exponential constants are described by quadratic functions in the investigated b range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not.

Turbulent rectangular compound open channel flow study using multi-zonal approach

“…It has been found in this study that the interface zones 2 and 3 in Fig. 8 are accounted for about 10-25% of the distance for main-channel and floodplain respectively (agreed with findings by experimental studies on various channel flows in [6,10]. In comparison, the shallower zone 3 is lengthier than zone 2 as the secondary flow has less depth of water to evolve vertically.…”

“…In Eqs. (8)- (10), is secondary flow parameter; S o is bed slope; g is gravitational acceleration; and A 1 , A 2 , k, and are all coefficients used for depth-averaged velocity formulation.…”

Pier Scour Prediction in Non-Uniform Gravel Beds

“…Qi et al [5] performed a field scour analysis and came to the conclusion that the access allowance through the embankment and scour at bridge foundations are the main causes of bridge failure. Therefore, the estimation of the amount of scour is necessary for designing an economical and safe bridge structure [1,[8][9][10].…”

“…In terms of flow conditions, the local scour for both clear-water and live-bed conditions has been extensively studied and several approaches, along with mathematical relationships, have been found [2][3][4]8,12]. Numerous studies have been completed to calculate the scour depth around the bridge piers [3,5,7,[9][10][11][12][13][14][15][16][17]. Most of these studies were conducted for uniform sediment beds and several relationships were developed after analyzing the experimental datasets at the laboratory scale only.…”

Effect of Pressure Fluctuations and Flow Confinement on Shear Stress in Jet-Driven Scour Processes

“…In addition, scour phenomena in natural rivers or streams could be characterized by different mechanisms, depending on in situ conditions (bed irregularity, presence of vegetation, flow characteristics, etc.). In this regard, it is worth mentioning that [31] have recently investigated 3D turbulence characteristics of different accelerating and decelerating flows, showing that the decelerating flow has a greater influence on the turbulence structure of flow in comparison to that of the accelerating one. Likewise, [32] analyzed both velocity distribution and three-dimensional turbulence characteristics for uniform smooth bed, laboratory-prepared rough bed and water-worked bed open channel flows.…”