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Old   May 31, 2006, 13:18
Default Force calcs by body section
  #1
Roland
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Hi

Im working with a car model. I want to calculate lift and drag forces by body component (i.e. wheel, hood, roof, etc) to determine effect on aerodynamic balance of body changes. Is there a mechanism withing Post that will allow me to define a subsection of my grid for this purpose?

It seems to me that, if I had to re-mesh, I could use virtual topology to combine areas of interest (i.e. combine the components that make up the tail section into a single virtual surface). But, the values I get when I tried this route are whacky (i.e hood lift is shown as 13,000 lbf) on a full scale model, even though the global values for body lift/drag are very close to wind tunnel data.

Any thoughts are greatly appreciated. Roland
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Old   May 31, 2006, 13:59
Default Re: Force calcs by body section
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Roland
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Sorry to followup on my own post, but Im assuming my virtual topology numbers are actually correct- I did not include ambient pressure over that area, which would account for the crazy numbers. Duh!

Still, can someone let me know if there is a way to partition out areas of a results file for analysis of forces on subsections? Doing this as virtual topology is not always appropriate, since that is dependent on the CAD geometry/source which may not have surfaces segmented as I want to study them.

Best, Roland
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Old   June 1, 2006, 17:06
Default Re: Force calcs by body section
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Jason
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Look into the interpolation tool which can be used to generate difference parameters between results files. The difference paramaters are then available in Post.

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Old   June 1, 2006, 17:17
Default Force calcs, comparing results in Post
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Roland
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Jason

I had tried Interpolation between 2 results files- where the only difference between the simulations was the inlet velocity. Unfortunately, Interpolation does not seem to create a 'Difference Force' paramater, but it does create many others- i.e. 'Difference Pressure'. Because of this, any vector plot or function calculator involving Force always includes ambient pressure (1 atm). Since a 'Difference Force' parameter is not apparently calculated, Interpolation does not help in determining relative forces. I dont know why Interpolation does not seem to calculate delta for Force, but I cannot find a way around that. Any ideas? Or, maybe there is another approach?

Again, my goal is simply to determine the force (lift as a positive or negative component) by area on an automobile at various speeds, which was something easy to do in another CFD package I used with a previous employer.

Best, Roland
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