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Old   April 18, 2011, 17:13
Default a very basic question regarding Re
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Hassan
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i want to ask that whether it is possible or not:

An author has compared his numerical results of water with the experimental results of air...

[the experimental results are not non dimensional results as on y-axis the units are mm and on the x-axis the units of velcoity cm/s are there]

Now suppose the author has used the non dimensional form of incompressible Navier stokes equations so we have 1/Re on the RHS of NS.

So if he keeps the dimensions of the experimental set up in his numerical study, can he get the same velcoity profile with water to that of the experimental profiles of air??

The author has not clearly mentioned that whom he is comparing his results to...so thats why im confused.. may be he is validating air to air just to see whether code works and afterwards focusing on the water that is his area of focus..
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Old   April 19, 2011, 09:15
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Hey,

You have probably as I understand to calculate the Reynolds number for the experiment because you know the Reynolds number in you numerical simulation.

If you have the same Reynolds number, you will have the same velocity profile for the air and water.


What's the reference of the paper?

Thomas
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Old   April 19, 2011, 10:51
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yeah exactly im confused as the guy is just comparing the two results at two different Re.

Thing im not able to understand is that if Re is same does this means tht every velocity profile of any fluid at same Re will be the same?? should nt be there any difference in the profiles??

take care
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Old   April 20, 2011, 11:23
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There's no difference between the profiles
That's the Beauty of the Dimensionless that gives you Dynamical similarity.

You can go in the Book of G.K. Batchelor, An introduction to Fluid Dynamics,(1967),Cambridge university press. Chap 4 section 7.

Thomas
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Old   April 20, 2011, 11:30
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thanks for the reference ...

so even if the results given in the experimental work are dimensional we can do compare the numerical results.

the paper im talking bout is

"numerical study of the impact of non Newtonian blood behaviour on flow over a two dimensional backward facing step" Biorehology volume 42 year 2005

i know the dynamic similarity but as the results in experiemntal study are dimensional so i still think that we cant compare the numerical results just on the basis of Re similarity.. the results tht we will get form numerical calculation will be non dimensional results ..

if u kindly take a look at this paper and check its validation part... he is comparing the numerical blood flow to the air (dimensioanl results)//

thanks you and kind regards
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