Related Experiment Video
Updated: Jun 2, 2026
11:51
Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
Precessive sand ripples in intense steady shear flows.
Juan M Restrepo1, Derek E Moulton, Hermann Uys
1Department of Mathematics, University of Arizona, Tucson, Arizona 85721, USA.
Summary
Experimental fluid dynamics reveal how shearing flows create large sand bars. Precessive bars show exponential growth in sediment transport with shear velocity, leading to new formulas for sediment transport rates.
Area of Science:
- Fluid dynamics
- Sediment transport
- Geomorphology
Background:
- Large-amplitude bars form in shearing fluid flows.
- Understanding bar formation dynamics is crucial for sediment transport modeling.
Purpose of the Study:
- To experimentally observe and analyze large-amplitude bar formation under shearing fluid action.
- To develop analytical expressions for bar precession speed and sediment transport rates.
- To investigate the limitations of classical mass flux parametrizations.
Main Methods:
- Experiments conducted in an annular tank with sheared water.
- Observation of various erodible bed manifestations: advective, precessive, interactive, and dispersive bars.
- Analysis of precessive bars, including skin depth and precession speed.
- Numerical flow calculations over experimental bar formations.
Main Results:
- Precessive bars exhibit exponential growth of skin depth with shear velocity.
- An analytical expression for precession speed and a formula for sediment transport rate were derived.
- Numerical simulations revealed shortcomings in classical mass flux parametrizations.
- Bar aspect ratio remained relatively constant over time.
Conclusions:
- The study provides new insights into the dynamics of large-amplitude bar formation in shearing flows.
- Derived formulas offer improved approximations for sediment transport rates.
- Findings highlight the need for refined models in complex flow conditions.
Related Concept Videos
01:24Rapidly Varying Flow
Rapidly varying flow (RVF) in open channels is characterized by abrupt changes in flow depth over a short distance, with the rate of depth change relative to distance often approaching unity. These flows are inherently complex due to their transient and multi-dimensional nature, making exact analysis difficult. However, approximate solutions using simplified models provide valuable insights into their behavior.Key Features of Rapidly Varying FlowRVF is commonly observed in scenarios involving...
01:29Gradually Varying Flow
Gradually varying flow (GVF) in open channels describes situations where water depth changes slowly along the channel due to factors like non-uniform bed slope, channel shape variations, or obstructions. This flow type occurs when the depth adjusts gradually to balance gravitational forces, shear forces, and energy requirements, resulting in a low rate of depth change.Characteristics of Gradually Varying FlowGVF is commonly observed in natural streams, rivers, and canals, where flow depth...
01:28Irrotational Flow
Irrotational flow is characterized by fluid motion where particles do not rotate around their axes, resulting in zero vorticity. For a flow to be irrotational, the curl of the velocity field must be zero. This imposes specific conditions on velocity gradients. For instance, to maintain zero rotation about the z-axis, the gradient condition:
01:27Steady Flow of a Fluid Stream
Consider a control volume, such as a pipe with solid boundaries, through which fluid flows and changes direction due to the impulse exerted by the resulting force from the pipe walls. In steady flow, the mass of fluid entering the control volume at a given time, t, with velocity v1, is equal to the mass leaving after infinitesimal time dt, with velocity v2.
During this process, the momentum of the fluid within the control volume remains constant over the time interval dt. By applying the...
During this process, the momentum of the fluid within the control volume remains constant over the time interval dt. By applying the...
01:17Steady, Laminar Flow Between Parallel Plates
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
01:22Couette Flow
Couette flow represents the flow of fluid between two parallel plates, with one plate fixed and the other moving with a constant velocity. This configuration allows for a simplified analysis using the Navier-Stokes equations, which govern fluid motion under conditions of viscosity and incompressibility. For Couette flow, the assumptions include a steady, laminar, incompressible flow with a zero-pressure gradient in the flow direction. This flow type is beneficial for understanding shear-driven...