Linear stability of sand waves sheared by a turbulent flow

2021 ◽  
Author(s):  
Subhasish Dey ◽  
Rajesh K. Mahato ◽  
Sk Zeeshan Ali
Keyword(s):  
Turbulent Flow ◽  
Linear Stability ◽  
Sand Waves

Numerical simulation of sand waves in a turbulent open channel flow

2014 ◽  
Vol 753 ◽  
pp. 150-216 ◽  
Author(s):  
Ali Khosronejad ◽  
Fotis Sotiropoulos
Keyword(s):  
Turbulent Flow ◽  
Numerical Simulations ◽  
Coherent Structures ◽  
Open Channel ◽  
Good Accuracy ◽  
Spectral Gap ◽  
Three Dimensional ◽  
Sand Wave ◽  
Sand Waves ◽  
Mobile Bed

AbstractWe develop a coupled hydro-morphodynamic numerical model for carrying out large-eddy simulation of stratified, turbulent flow over a mobile sand bed. The method is based on the curvilinear immersed boundary approach of Khosronejad et al. (Adv. Water Resour., vol. 34, 2011, pp. 829–843). We apply this method to simulate sand wave initiation, growth and evolution in a mobile bed laboratory open channel, which was studied experimentally by Venditti & Church (J. Geophys. Res., vol. 110, 2005, F01009). We show that all the major characteristics of the computed sand waves, from the early cross-hatch and chevron patterns to fully grown three-dimensional bedforms, are in good agreement with the experimental data both qualitatively and quantitatively. Our simulations capture the measured temporal evolution of sand wave amplitude, wavelength and celerity with good accuracy and also yield three-dimensional topologies that are strikingly similar to what was observed in the laboratory. We show that near-bed sweeps are responsible for initiating the instability of the initially flat sand bed. Stratification effects, which arise due to increased concentration of suspended sediment in the flow, also become important at later stages of the bed evolution and need to be taken into account for accurate simulations. As bedforms grow in amplitude and wavelength, they give rise to energetic coherent structures in the form of horseshoe vortices, which transport low-momentum near-bed fluid and suspended sediment away from the bed, giving rise to characteristic ‘boil’ events at the water surface. Flow separation off the bedform crestlines is shown to trap sediment in the lee side of the crestlines, which, coupled with sediment erosion from the accelerating flow over the stoss side, provides the mechanism for continuous bedform migration and crestline rearrangement. The statistical and spectral properties of the computed sand waves are calculated and shown to be similar to what has been observed in nature and previous numerical simulations. Furthermore, and in agreement with recent experimental findings (Singh et al., Water Resour. Res., vol. 46, 2010, pp. 1–10), the spectra of the resolved velocity fluctuations above the bed exhibit a distinct spectral gap whose width increases with distance from the bed. The spectral gap delineates the spectrum of turbulence from the low-frequency range associated with very slowly evolving, albeit energetic, coherent structures induced by the migrating sand waves. Overall the numerical simulations reproduce the laboratory observations with good accuracy and elucidate the physical phenomena governing the interaction between the turbulent flow and the developing mobile bed.

Linear Stability of Turbulent Flow Profiles

1971 ◽  
Vol 14 (7) ◽  
pp. 1323 ◽  
Author(s):  
Merle C. Potter
Keyword(s):  
Turbulent Flow ◽  
Linear Stability ◽  
Flow Profiles

Theoretical Analysis and Numerical Simulation of Turbulent Flow Around Sand Waves and Sand Bars

2009 ◽  
Vol 21 (2) ◽  
pp. 292-298 ◽  
Author(s):  
Shi-he Liu ◽  
Xiao-yuan Xiong ◽  
Qiu-shi Luo
Keyword(s):  
Numerical Simulation ◽  
Theoretical Analysis ◽  
Turbulent Flow ◽  
Sand Waves ◽  
Sand Bars

scholarly journals Modelling the two-way coupling of tidal sand waves and benthic organisms: a linear stability approach

2019 ◽  
Vol 19 (5) ◽  
pp. 1073-1103 ◽  
Author(s):  
Johan H. Damveld ◽  
Pieter C. Roos ◽  
Bas W. Borsje ◽  
Suzanne J. M. H. Hulscher
Keyword(s):  
Linear Stability ◽  
Benthic Organisms ◽  
Sand Waves ◽  
Tidal Sand

On the genesis and evolution of barchan dunes: morphodynamics

2017 ◽  
Vol 815 ◽  
pp. 117-148 ◽  
Author(s):  
A. Khosronejad ◽  
F. Sotiropoulos
Keyword(s):  
Turbulent Flow ◽  
Transverse Waves ◽  
Sand Waves ◽  
Eddy Simulation ◽  
Term Evolution ◽  
Large Eddy ◽  
Barchan Dunes ◽  
Emergent Structure ◽  
Conventional Models

Barchan dunes are crescent-shaped formations of sand that can dominate both desert and subaqueous landscapes when the supply of sand is scarce. Because of the complexity and scale of the underlying phenomena, the mechanisms governing the entire process from the genesis to the long-term evolution of barchan fields still remain to be better understood. Herein, we attempt to present a description of this process in a subaqueous environment by employing a large-eddy simulation approach that couples turbulent flow and sand-bed morphodynamics. We show that the seeds of the emergent structure in barchan fields are random turbulent flow motions near the initially flat bed. We also provide high-resolution insights into phenomena such as barchan migration and merging, and show how transverse sand waves are formed and migrate over the barchan horns. Furthermore, the transverse sand waves over the barchan horns are shown to be the seeds of the newly born barchans at the end points of the two horns of a barchan through the process known as calving. To show this, we examine the celerity, wavelength and amplitude of the transverse sand waves over the barchan as they approach the end of its horn. The celerity and wavelength of these transverse sand waves are shown to be the defining factors in determining the frequency of the calving process. The amplitude of the newly born barchans (through calving) is also shown to be associated with the amplitude of the transverse waves near the end of the horn. The simulation data also show that the wavelength of the newly born barchans (the distance between individual dunes) is closely related to that of the transverse sand waves over their maternal barchan. Finally, we use the simulation results to discuss past conclusions derived from theory, conventional models and field observations.

A linear stability analysis of tidally generated sand waves

2000 ◽  
Vol 417 ◽  
pp. 303-322 ◽  
Author(s):  
THEO GERKEMA
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Sand Wave ◽  
Length Scale ◽  
Wave Regime ◽  
Sand Waves ◽  
Initial Stage ◽  
Bed Slope ◽  
Two Parameters

A linear stability analysis is carried out to examine the initial stage of sand-wave growth under tidal flows and the occurrence of a preferred length scale. The fact that these bedforms typically have length scales small compared to the tidal excursion is exploited by adopting an asymptotic approach to solve the hydrodynamic part of the problem, i.e. to find the hydrodynamic response to an initially small bed perturbation. This method is shown to have important advantages over previously used methods, since it allows an exploration of the complete sand-wave regime (whereas other methods fail for short sand waves), and in general it is also more accurate. It is found that the selection of a preferred length scale depends mainly on only two parameters (the bed-slope coefficient, and the ratio of friction velocity to eddy viscosity), whereas there appears to be almost no dependence on the water depth.

An Introduction to Turbulent Flow

2000 ◽  
Author(s):  
Jean Mathieu ◽  
Julian Scott
Keyword(s):  
Turbulent Flow

Modal Analysis of Turbulent Flow near an Inclined Bank–Longitudinal Structure Junction

2021 ◽  
Vol 147 (3) ◽  
pp. 04020100
Author(s):  
Nasser Heydari ◽  
Panayiotis Diplas ◽  
J. Nathan Kutz ◽  
Soheil Sadeghi Eshkevari
Keyword(s):  
Turbulent Flow ◽  
Modal Analysis ◽  
Longitudinal Structure

Numerical simulation of subsonic turbulent flow of oscillating NACA 0015 airfoi

2018 ◽  
Vol 2 ◽  
pp. 133-145
Author(s):  
D.O. Redchyts ◽  
◽  
S.V. Moiseenko ◽  
Keyword(s):  
Numerical Simulation ◽  
Turbulent Flow ◽  
Naca 0015
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