CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Autodesk Simulation CFD (
-   -   Incorrect result from autodesk lab project falcon...plz guide... (

addy01 February 24, 2013 14:03

Incorrect result from autodesk lab project falcon...plz guide...
1 Attachment(s)
What is Fd stand for in FALCON result? And if it is drag force then why am i getting lower drag force via calculation by using same coefficient of drag as shown in falcon.I m getting Cd approx 1.22 on a block of 1 m^2 cross section at the speed of 10m/s. then how it is possible that drag force calculated by the falcon is 83.189 N?? (Attached Photo)
While I am using formula for drag force .5*Cd*(rheo)*A*V^2 then i am getting 74.725 N (assuming the density of air 1.225 kg/m^3)...plz help if u can its really important for my project...or suggest me any alternative way...
Thanks & Regards..

marktm250xc February 28, 2013 13:57

Since this is newer technology, the Adesk folks may have to chime in.

The drag force, Fd, is typically first computed by summating all of the pressures acting on each element face of the body.

The Cd is then computed using Fd, along with the density, velocity, which are known inputs. The only other variable is the area, the calculation of wihch could be mesh dependent, but for a block, I would not expect much error there.

1.22 is just about right for a flat plate normal to the flow.

ryan.arnaudin March 1, 2013 13:09

This was also posted to the Autodesk forums around the same time, and one of the PMs has answered there.

addy01 March 2, 2013 04:15

actaually it ws posted by me but i m unable to take should i use it for my project or not?? cn i calculate some approximate factor for correct result then multiply tat factor in every result i get fro most accurate answer..actually i m working on a project of aerodynamics of heavy vehicles...plz reply/...thnx 4 d help :)

marktm250xc March 2, 2013 17:42

Have you implemented the suggestions of further refinement of the mesh and also increasing the size of your domain? If so, what was the outcome compared to the original run.

Last I knew, Falcon was a still a free "preview" so I am not sure how far along it would be in the QA process. But whether it is a preview, freeware like OpenFOAM or higher-end commercial software, due diligence is on the end user for correct application of the tool.

addy01 March 3, 2013 08:16

getting different coefficient of drag & drag force for diff. wind tunnel size..
4 Attachment(s)
I am getting different value of Drag Force Fd & Coefficient of Drag for a verticle plate of 1 m^2 cross sectional area and 100 mm thickness while changing the wind tunnel size in project Falcon by autodesk (I attached photo of analysis with different wind tunnel size..take a look). plz help me to decide optimal size of virtual wind tunnel in falcon so that i can get correct answer..Wht is the volume stand for that i highlighted in the pics??

All times are GMT -4. The time now is 18:43.