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-   -   Usefulness of Similarity theory in External Aero (http://www.cfd-online.com/Forums/main/12792-usefulness-similarity-theory-external-aero.html)

 Amod Kumar January 10, 2007 03:14

Usefulness of Similarity theory in External Aero

Hi,

I am simulating external aerodynamic simulation of an automobile body. I am using symmetrical half. As per standard recommended practice, the computational domain should be 8L X 4L X 2L in longitudinal, transverse and vertical direction.

However, I have a machine limitation with mesh size restricted to < 1 million elements. It seems impossible to squeeze the number within this limit.

I resorted to use Similarity analysis to reduce the domain size. I have scaled down the computational domain by a factor of 16 and increase the inlet velocity 16 times to ensure dynamic similarity (constant Re for model and prototype).

Can anyone suggest the imlication of such simulation strategy on final result (vis-a-vis drag forces)?

Thanks,

Amod Kumar

 dhy January 10, 2007 03:42

Re: Usefulness of Similarity theory in External Ae

Hi Amod, The problem has become interesting due to the limitations you are playing with. I have never worked on such problems, however, I am telling whatever little I know. I think you might have taken care of to check the change in Hydraulic Diameter u r using in the Re No constant. Otherwise you may end up with errouneous results. Cheers.

 rt January 10, 2007 05:58

Re: Usefulness of Similarity theory in External Ae

dear amod

i think u miss a main issue in your dimensional analysis,

note that at first u have physical spatial and temporal scales (imposed by your system behavior and phenomena under study) that are used for generation of dimensionless system.

In ur strategy, u decrease physical spatial scale by factor 16, this leads to decreasing ur mesh size (new simulation) by factor 16 for generation of previous results!!!

so u don't acquire anything, else if your solver is not dimensionless u may increase effect of ploating poits errors.

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