CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Force calcs by body section (

Roland May 31, 2006 13:18

Force calcs by body section

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

Roland May 31, 2006 13:59

Re: Force calcs by body section
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

Jason June 1, 2006 17:06

Re: Force calcs by body section
Look into the interpolation tool which can be used to generate difference parameters between results files. The difference paramaters are then available in Post.

Roland June 1, 2006 17:17

Force calcs, comparing results in Post

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

All times are GMT -4. The time now is 07:16.