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Are two simulations equivalent if they have the same Grassof and Reynolds?

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Old   November 10, 2017, 12:01
Default Are two simulations equivalent if they have the same Grassof and Reynolds?
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Hector Redal
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Hi,

I would like to know if two simulations that have the same Reynolds and Grassof number are thermally equivalent?

I am trying to simulate the problem described in the following article:
http://heattransfer.asmedigitalcolle...icleid=1438948

I am supposing air with Pr = 0.71.
When I double the viscosity, doubling the inlet velocity (keeping reynolds number), and doubling the temperature difference in the formula for calculating the Grashof number, the results I am obtaining are different.
I have always understood that non-dimensional number allow comparison between different simulations/experiments that show same behaviour.

May I am missing something?

As thermal coefficient expansion (beta) for the Grashof number I am using 1/T, being T the low temperature in the problem.

Should I use any other value for the temperature (i.e., the high temperature)? The middle temperature in the range?

Any comment is welcome.

Best regards,
Hector.
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Old   November 10, 2017, 12:10
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Filippo Maria Denaro
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You can easily answer by looking at the governing equations in non-dimensional form. If you have the same non dimensional parameters the two non-dimensional solutions must be the same.
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Old   November 10, 2017, 20:26
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Hector Redal
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Quote:
Originally Posted by FMDenaro View Post
You can easily answer by looking at the governing equations in non-dimensional form. If you have the same non dimensional parameters the two non-dimensional solutions must be the same.
This was also my understanding, but what I am observing is not this.
The non-dimensional solution differ by almost 5%.
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Old   November 11, 2017, 04:27
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Filippo Maria Denaro
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There is a difference in the two simulation, maybe different iteration accuracy
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Old   November 13, 2017, 12:32
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Hector Redal
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Quote:
Originally Posted by FMDenaro View Post
There is a difference in the two simulation, maybe different iteration accuracy
If I run a simulation without solving the energy equation, the difference between two solution having the same non-dimensional numbers (but using different values for velocity, or density, or viscosity, etc.) is almost zero.

I only observe this discrepancy when trying to solve a problem with energy equation coupled. The difference between both solutions is more ore less 5%. No more.
For me, it's more than can be justified by the accuracy iteration. Maybe I am wrong.
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