Flow-velocity fluctuations and the intensity of turbulence
Turbulent flow is characterized by eddies, which produce fluctuations in the velocity of the flow.
Learning Goals
- Be able to decompose flow velocities into a mean velocity and velocity fluctuations
- Know that these fluctuations are caused by turbulence and grow greater with more intense turbulence
- Visually connect the shapes of eddies to their impact on flow-velocity variability
Eddies and visualizing turbulent fluctuations in a flow
Zones of whirling flow in rivers (and in fluids in general) are known as “eddies”. These eddies characterize a turbulent flow. They impact the fluid velocity field. The numerical simulations shown in this video can give you an idea of what eddies look like in flows:
In the following video, a plate is moved to the right across the top of the flume, shearing the fluid and thereby producing turbulent eddies. Look at the cases with different Reynolds numbers, and think about what produces the higher intensity of turbulence. How do you think that these might relate to the amount of shear experienced by the fluid, and to the fluid velocity?
Thank especially about how this turbulence may impact flow velocities at a point! That is the topic of this lesson.
Turbulence and flow velocity (and its variability)
Turbulence causes flow velocities to become noisy. Why is this, and how does this relate to the eddies that characterize turbulent flow?
Course notes
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