Does this vorticity plot make sense?

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Discussion Overview

The discussion centers around the interpretation of a vorticity plot for lid-driven cavity flow in a two-dimensional context. Participants are examining the expected behavior of the vorticity field, particularly in relation to the flow direction and the characteristics of the shear layer.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expects the vorticity field to be predominantly negative due to the clockwise flow and the right-hand rule, but observes unexpected behavior in the plot.
  • Another participant, lacking prior knowledge of the flow, finds the plot reasonable and questions what seems weird about it.
  • A participant notes that if the outer parts of the flow do not rotate quicker than the inner parts, negative vorticity is not necessary throughout the entire plane, highlighting surprise at the large negative vorticity observed at the upper edge.
  • Another participant agrees with the presence of large negative vorticity at the upper part, attributing it to a free shear layer, but raises questions about the units of measurement and the free stream velocity.
  • This participant also discusses the generation of positive vorticity along the wall due to the boundary layer and speculates on how changes in the flow's rotation speed could affect the characteristics of this vorticity layer.

Areas of Agreement / Disagreement

Participants express differing views on the expected behavior of the vorticity field, particularly regarding the presence and implications of negative and positive vorticity. The discussion remains unresolved with multiple competing interpretations.

Contextual Notes

Participants mention missing information such as the units of measurement and the free stream velocity, which may affect the interpretation of the vorticity plot.

Who May Find This Useful

Individuals interested in fluid dynamics, particularly those studying vorticity in two-dimensional flow scenarios, may find this discussion relevant.

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I'm trying to plot the vorticity field for lid-driven cavity flow. Because I'm looking at 2D flow, the vorticity is plotted as a scalar field The flow field is clockwise, and I would expect the majority of the resulting vorticity field to be negative (right hand rule). However, it seems as thought it has some weird behavior. What do you think?

http://i.imagebanana.com/img/h3ke22hx/Selection_049.png
 
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Having never studied or even read anything about this flow, I would say it looks reasonable. What do you think is weird about it?
 
If the outer parts do not rotate quicker than the inner parts, you don't need a negative vorticity in the whole plane. The upper edge is a bit surprising with its large negative vorticity.
 
The large negative vorticity at the upper part is exactly what I would have expected since it is a free shear layer. Of course I don't know what the magnitude should be, and we don't know what the units are.

What are the units? Also, what is the free stream velocity?

As the flow turns down near the far right edge, positive vorticity is generated along the wall due to the boundary layer that forms on that surface. Positive vorticity would form along the walls regardless of how quickly the outer and inner parts are rotating (as long as they are rotating and generating a flow along the walls). If the flow were rotating faster I would expect the layer of positive vorticity to become thinner and for its magnitude to increase.
 

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