The structure of turbulent flow in an open channel bend of strong curvature with deformed bed: Insight provided by detached eddy simulation

Date

2011-05-12

Author

Constantinescu, George
Köken, Mete
Zeng, Jie

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

198
views

0
downloads

[1] Results of a detached eddy simulation (DES) are used to better understand the effects of the mean flow three-dimensionality and secondary currents on turbulence and boundary shear stresses and the mechanisms through which the momentum and Reynolds stresses are redistributed in a strongly curved 193 degrees bend with fixed deformed bed corresponding to the later stages of the erosion and sedimentation process. The ratio between the radius of curvature of the curved reach and the channel width is close to 1.3. The large channel curvature and the point bar induce flow separation near the inner bank and the formation of several strong separated shear layers (SSLs), where production by mean shear dominates. DES shows that in addition to the main cell of cross-stream circulation developing in the deeper part of the bend, several streamwise-oriented vortices (SOV) form at the inner bank. DES satisfactorily captures the distribution of the streamwise velocity and streamwise vorticity in relevant cross sections compared to experiment. Comparison with a Reynolds-averaged Navier-Stokes (RANS) simulation shows that DES predicts more accurately the velocity redistribution and cross-stream motions in the channel. This is because RANS significantly underpredicts the circulation and turbulence amplification inside the cores of the SOV vortices. DES is then used to clarify the influence of the SOV vortices and SSLs on the boundary shear stress. DES reveals the presence of several regions of large amplification of the pressure RMS fluctuations near the inner and outer banks, which can locally increase the bed erosion and affect the bank stability in the case of a bend with erodible banks. The mean flow bed shear stress distribution predicted by DES is significantly different than that predicted by RANS, while DES predictions of the mean flow are more accurate. This means that use of eddy-resolving techniques like DES in mobile bed simulations of flow in curved alluvial channels should result in more accurate predictions of bathymetry.

Subject Keywords

Water Science and Technology

URI

https://hdl.handle.net/11511/47326

Journal

WATER RESOURCES RESEARCH

DOI

https://doi.org/10.1029/2010wr010114

Collections

Department of Civil Engineering, Article

Suggestions

OpenMETU
Core

An investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel: 2. Conditions corresponding to the final stages of the erosion and deposition process Köken, Mete (American Geophysical Union (AGU), 2008-08-05) Large eddy simulation (LES) is used to investigate the flow around a vertical spur dike in a straight channel with equilibrium scour bathymetry and the scour mechanisms in the later stages of the erosion deposition process. The equilibrium bathymetry is obtained from an experiment conducted at the same relatively low channel Reynolds number (Re = 18,000). Flow visualizations are used to complement the information obtained from the numerical simulation. The present investigation demonstrates that large-scale...
An investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel: 1. Conditions corresponding to the initiation of the erosion and deposition process Köken, Mete (American Geophysical Union (AGU), 2008-08-05) The present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start (flat bed) of the scouring process. Large eddy simulation (LES) is performed at a relatively low channel Reynolds number (Re = 18,000), in the range where most flume studies with clear water scour conditions are conducted. Similar to these studies, the incoming flow is fully turbulent and conta...
A double-porosity model for a fractured aquifer with non-Darcian flow in fractures Altinors, Altay; Onder, Halil (Informa UK Limited, 2008-08-01) Non-Darcian flow in a finite fractured confined aquifer is Studied. A stream bounds the aquifer at one side and all impervious Stratum at the other. The aquifer consists of fractures capable of transmitting water rapidly, and Porous blocks which mainly store water. Unsteady flow in the aquifer due to a Sudden rise in the stream level is analysed by the double-porosity conceptual model. Governing equations for the flow in fractures and blocks are developed using the continuity equation. The fluid velocity in...
STOCHASTIC-ANALYSIS OF FIELD MEASURED UNSATURATED HYDRAULIC CONDUCTIVITY Ünlü, Kahraman; NIELSEN, DR (American Geophysical Union (AGU), 1989-12-01) Unsaturated hydraulic conductivity K values as a function of soil‐water pressure head h were measured in the soil at 75 cm depth at 70 different sites separated from one another by a distance of l m along a horizontal transect. K field was viewed as a random function of spatial location x. Field data were analyzed (1) to examine the isotropy and stationarity of K, (2) to check the ergodicity of K in the mean and covariance functions, and (3) to characterize the distribution properties of K by estimating the...
Comparison of prognostic and diagnostic surface flux modeling approaches over the Nile River basin Yılmaz, Mustafa Tuğrul; Zaitchik, Ben; Hain, Chris R.; Crow, Wade T.; Ozdogan, Mutlu; Chun, Jong Ahn; Evans, Jason (American Geophysical Union (AGU), 2014-01-01) Regional evapotranspiration (ET) can be estimated using diagnostic remote sensing models, generally based on principles of energy balance closure, or with spatially distributed prognostic models that simultaneously balance both energy and water budgets over landscapes using predictive equations for land surface temperature and moisture states. Each modeling approach has complementary advantages and disadvantages, and in combination they can be used to obtain more accurate ET estimates over a variety of land...

Citation Formats

G. Constantinescu, M. Köken, and J. Zeng, “The structure of turbulent flow in an open channel bend of strong curvature with deformed bed: Insight provided by detached eddy simulation,” WATER RESOURCES RESEARCH, pp. 0–0, 2011, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/47326.