Does inviscid mean shear stress is negligible?

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Discussion Overview

The discussion revolves around the concept of inviscid flow and its implications for shear stress in fluid dynamics, particularly in the context of calculating drag on a sphere immersed in water. Participants explore the relationship between Reynolds number and the assumption of negligible shear stress.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that a Reynolds number of 10^5 is sufficient to treat the fluid as inviscid, questioning if this implies shear stress can be neglected.
  • Another participant emphasizes the need to define "inviscid" and argues that a high Reynolds number does not automatically allow for ignoring shear stress, pointing out the importance of the object under consideration.
  • A participant describes the specific scenario of a sphere in water and references the drag calculation formula, noting the lack of information on shear stress and suggesting that it might be negligible due to the high Reynolds number.
  • One reply cautions that while inviscid flow can be assumed, it may not be accurate without knowing the viscosity or the specific fluid properties.
  • A later post reiterates that "inviscid" means non-viscous flow, implying that shear stresses are minimal and can be neglected, aligning with the initial query about the assumptions made at high Reynolds numbers.

Areas of Agreement / Disagreement

Participants express differing views on whether a high Reynolds number allows for the assumption of negligible shear stress. There is no consensus on the accuracy of treating the flow as inviscid in this context.

Contextual Notes

Participants highlight the importance of defining terms and the specific conditions of the fluid and object involved, indicating that assumptions may depend on additional factors such as viscosity and flow characteristics.

corona7w
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I have this flow with Reynold's number in the 10^5, which I think it's big enough to treat the fluid as inviscid, does this also mean I can assume the shear stress is negligible?
 
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First, what does inviscid mean, by definition?

Second, just because the flow is 10^5 does not mean you can ignore shear stress. What is the object under consideration?
 
It's a sphere with radius R immersed in water of velocity V. I'm asked to calculate the drag on it. I know the formula for drag is integral of Pcos theta dA + integral of shear stress sin theta dA . And I am not given any information regarding the shear stress, so I thought since the Re is pretty big, we might just treat the shear stress as negligible so only the first term of the equation needs to be calculated.
 
You could assume inviscid flow but its probably not an accurate assumption. Whats the viscosity or what fluid are you using?
 
Last edited:
corona7w said:
I have this flow with Reynold's number in the 10^5, which I think it's big enough to treat the fluid as inviscid, does this also mean I can assume the shear stress is negligible?

If u are talking about term "Inviscid"...then u are correct.. its means flow is non viscous ,,,that in return means SHEAR STRESSES are minimum and can be neglected
 

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