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-   -   Inquiry, post results on airflow over auto body (http://www.cfd-online.com/Forums/cfx/22682-inquiry-post-results-airflow-over-auto-body.html)

Roland June 8, 2006 17:54

Inquiry, post results on airflow over auto body
 
Hello-

I have a solidworks model of an auto body imported into Ansys for mesh/cfd analysis. The chassis is split on the centerline to facilitate a symmetry approach for reduced overhead.

One of my goals is to determine forces on sections of the body (i.e. the hood)- in particular, lift.

Initially, my results we biased due to reference pressure remaining at 1 Atm. So, I set reference pressure to 0 Atm, and that helped. However, I ran a few Vector plots of Force, and found that on various incarnations of the mesh (i.e. higher vs. lower cell count, larger vs. smaller wind tunnel, all on the same body), the vector results may show a 1 Atm bias (as if the chassis was operated at 2 Atm internally within a 1 Atm flow). In others, this effect does not appear. All use the same "Pre" configuration settings.

Im wondering if this problem might be a function of the mesh, where in some cases, the chassis is considered 'open' so that there is a balance of atmospheric pressure on both sides of the surface(s), and in other- the chassis is considered closed and operating at 1 Atm regardless of external static pressure (perhaps due to the symmetry plane?).

Any ideas as to why a simple symmetry body might indicate this behavior? I cannot find any commonalities that would explain it.

Best, Roland

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