Reynolds stress modeling of supercritical narrow channel flows using OpenFOAM: Secondary currents and turbulent flow characteristics

Abstract

In this study, the full Launder, Reece and Rodi pressure-strain model and nonlinear boundary damping functions were incorporated in OpenFOAM® to simulate the turbulence-driven secondary currents in supercritical narrow channel flows such as in sediment bypass tunnels (SBTs). Five simulations were performed under uniform flow conditions covering Froude numbers from 1.69 - 2.56 and aspect ratios (channel width to flow depth) ar from 0.9 - 1.91 to investigate the formation of secondary currents and their impacts on longitudinal velocity, turbulence characteristics, and bed shear stress distribution. The numerical results of the maximum longitudinal velocity and the average shear velocity show marginal deviations, of less than 2.6%, from two-dimensional experimental results acquired under decelerating flow conditions. However, some differences are observed for the secondary currents and for the vertical turbulence intensity and Reynolds shear stress in the outer flow region, especially for cases with higher flow nonuniformity (that can influence the surface perturbation) whose influence is missing in the numerical model. No intermediate vortex is observed for ar = 1.91. However, it develops for lower ar, and detaches from the free surface vortex when ar {less than or equal to} 1.05. Such vortex bulges the longitudinal velocity contour lines inward and the zone of higher longitudinal velocity narrows and deepens with a decrease in ar. The decrement reduces the magnitude of the normalized maximum secondary velocity. It also affects the bottom vortex which alters the bed shear stress distribution.

Direct numerical simulation of flow in open rectangular ducts

“…A similar trend was reported in the experiments of Demiral, Boes & Albayrak (2020) and the Reynolds-averaged Navier–Stokes (RANS) simulations of Kadia et al. (2022), who showed that secondary motions in open ducts have a topology similarity to those in closed ducts, although both studies featured flow in ducts with free surface in the supercritical regime, which is rather different from our flow case with a flat top surface. Additionally, RANS simulations should be taken with caution, as the prediction of secondary flows is not always accurate.…”

“…The secondary shear stress is nearly negligible on the bottom and sidewalls, although it has a comparable intensity with the other components at the bottom and top corners, suggesting that its mixing action is limited to the corner regions, whereas it is not relevant close to the side and bottom walls. Similar distributions of the Reynolds stresses τ 11 , τ 22 and τ 12 have also been observed in the studies of Demiral et al (2020) and Kadia et al (2022). This general organization is found regardless of the duct aspect ratio, although characterizing differences are visible, which are due to the imprint of the secondary flows.…”

“…(2020) and Kadia et al. (2022). This general organization is found regardless of the duct aspect ratio, although characterizing differences are visible, which are due to the imprint of the secondary flows.…”

Experimental and numerical investigations of the water surface profile and wave extrema of supercritical flows in a narrow channel bend

“…To achieve these goals, three tests were performed both experimentally and numerically for discharges Q = 0.045 m 3 /s, 0.07 m 3 /s, and 0.095 m 3 /s; approach flow depths h 0 = 0.109 m, 0.151 m, and 0.175 m; aspect ratios a r = 1.83, 1.32, and 1.14; and Froude numbers Fr ≈ 2. These tested a r and Fr values are comparable to that observed in existing SBTs 17 .…”

Improved efficiency with concave cavities on S3 surface of a rim-driven thruster

“…The k-x shear stress transport (SST) is one of the main turbulence models that we are aware of. 6,9 The cost and difficulty of this method are lower than DES (detached eddy simulation) and LES (large eddy simulation) according to Refs. 10 and 11.…”