# The reynolds number

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Good evening!

Could anybody inform me in which circumstances the reynolds number takes low or negative values?

Thank you!

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Re = ratio of inertial forces to viscous forces.... So you're going to get a very low number anytime you're moving very slowly through a very viscous fluid. I don't see how you'd ever get a negative value.

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Thank you for your reply...I have seen negative values in a paper that I read, but I thought it would be something wrong.

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Just a thought, incomplete at present - what if you are dealing with a Power Law fluid?

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The classically defined Reynolds number shouldn't ever be negative. $\textrm{Re} = \frac{vl \rho}{\mu}$ none of these terms can be negative, l is a characteristic length, v is a characteristic velocity, rho is the density, mu is the viscosity.

Now, that said, there are lots of times problem-specific Reynolds numbers are defined. e.g. ones for flow through a packed bed, or as Ophiolite above mentions, ones for non-Newtonian fluids. Now, that said, the specifics about the defined Re will be needed for how to correctly interpret it.

I will admit, I've never seen a negative one, unless someone naively just puts in a negative velocity. But, if they do that, they really are losing the meaning behind what the ratio is supposed to mean in the first place.

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The only way that I see a Reynolds number can become negative, is when the velocity or relevant length are negative. But that just means that whoever was measuring it, started measuring from the wrong side

Never seen a negative Re number before.

Leni, for more feedback it is probably a good idea to link to the paper, or give the reference. (We know it might not be freely available).

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Good evening!

Could anybody inform me in which circumstances the reynolds number takes low or negative values?

Thank you!

Tiny particles movement. But, is it in the range of the continuity fluid dynamics?

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