Related Experiment Video
Updated: Jul 17, 2026
11:51
Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
Large- and very-large-scale motions in channel and boundary-layer flows
1Department of Theoretical and Applied Mechanics, University of Illinois, Urbana, IL 61801, USA.
Summary
Large-scale motions (LSMs) and very-large-scale motions (very-LSMs) are crucial in pipe flow. Similar structures were found in channel and boundary layer flows, indicating common generation mechanisms despite geometric differences.
Area of Science:
- Fluid Dynamics
- Turbulence Research
- Aerodynamics
Background:
- Large-scale motions (LSMs) and very-large-scale motions (very-LSMs) dominate kinetic energy and Reynolds shear stress in pipe flow.
- Previous studies established the significance of these motions in pipe flows.
Purpose of the Study:
- To investigate the presence and characteristics of LSMs and very-LSMs in channel and boundary layer flows.
- To compare the properties of these large-scale structures across different canonical wall-bounded flows.
Main Methods:
- Utilized measurement and analysis techniques similar to those used in prior pipe flow studies.
- Extended investigations to channel and zero-pressure-gradient boundary layer flows.
Main Results:
- Very-LSMs in boundary layers are shorter than in pipe flow but exhibit similar behavior, suggesting common underlying mechanisms.
- Spectra of Reynolds shear stress-induced forces are comparable across pipe, channel, and boundary layer flows.
- Both very-LSMs and main turbulent motions contribute to flow deceleration above the Reynolds shear stress peak.
Conclusions:
- Large-scale turbulent structures are present in canonical wall flows beyond pipe flow.
- The outer geometry has a modifying influence, but fundamental mechanisms for LSMs and very-LSMs appear consistent.
- These motions play a significant role in the overall momentum transfer and flow deceleration.
Related Concept Videos
01:18Boundary Layer Characteristics
When a fluid encounters a solid surface, a boundary layer forms due to the interaction between the fluid's motion and the stationary surface. This phenomenon is characterized by a thin region adjacent to the surface where viscous forces dominate, influencing the fluid's velocity profile. The development of the boundary layer begins at the leading edge of the surface and evolves as the fluid moves downstream.As the fluid flows over the surface, friction between the fluid and the wall slows down...
01:07Laminar and Turbulent Flow
Fluid dynamics is the study of fluids in motion. Velocity vectors are often used to illustrate fluid motion in applications like meteorology. For example, wind—the fluid motion of air in the atmosphere—can be represented by vectors indicating the speed and direction of the wind at any given point on a map. Another method for representing fluid motion is a streamline. A streamline represents the path of a small volume of fluid as it flows. When the flow pattern changes with time, the streamlines...
01:23Introduction to Types of Flows
Fluid flows are categorized by dimensionality and behavior, with one-dimensional flow being the simplest form, where properties like velocity and pressure change only along a single axis. Water moving through straight pipes exemplifies this flow type, as variations in other directions are minimal. One-dimensional analysis helps simplify understanding such flows, focusing solely on changes along the pipe's length.
Two-dimensional flow involves changes in both length and height, as seen in air...
Two-dimensional flow involves changes in both length and height, as seen in air...
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...
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...
01:24Turbulent Flow
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent spots,...