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-   -   help in cfx-build 5.6 (http://www.cfd-online.com/Forums/cfx/19898-help-cfx-build-5-6-a.html)

FERNANDO VICENTE September 17, 2003 10:46

help in cfx-build 5.6
 
Hi, i have to simulate a flow over the car, and i have to make the model in the cfx-build. The model of the car i can import fro the other cad,but my question is,i have to enclose the car in a large box in the cad?or i have to create a 3d regions in cfx-build?

regards

fernando

Glenn Horrocks September 17, 2003 18:00

Re: help in cfx-build 5.6
 
Hi Fernando,

Have a look at tutorial 5, "Flow over a blunt body" in the documentation. It describes how to set up this type of problem. Also on the CFX community webpage there is further detail on this simulation, "External flow over an Ahmed body". It is worth a look as a simple comparison to experimental results is included.

But to answer your direct question, you can create the box around the car either in your CAD system and import it, or just import the car geometry and do the box in CFX-Build. Either way can work.

Regards, Glenn

fernando vicente September 17, 2003 21:41

Re: help in cfx-build 5.6
 
Hi Glenn ,first of all i thank you for your time and yours suggestions.

i saw the tutorial 5 but in this excercise the blount body is common ,there are no strange forms of the vehicle. in my case i have a model of the race car,such as NASCAR car,and i would like to know to reduce the number of nodes and the size of the file,if i need to make the full model or i can to make a half model. if i take account the effect of the tire on the ground,how i can to simulat this efect,in the tutorial 5 is very basic concept.

Another question is, i was thinking to import the car model from catia,i want to know if i make some points instead of the solid model and in the cfx-build create the car joints this point and create the surface and not to make the car such as solid .

could you understand me???

regards

fernando

Glenn Horrocks September 18, 2003 18:28

Re: help in cfx-build 5.6
 
Hi Fernando,

Even though your car is a racecar and is therefore a bit more streamlined than the Ahmed body shown in tutorial 5, the principles shown in that tutorial are still applicable. The example on the CFX-Community website is a bit more detailed and includes a validation of the model against experimental results. I highly recommend you look at it too.

As for whether you need to model half the car or the full car - that depends on what you are trying to model, but for a starting point I would model only half the geometry. Later on you can check whether the full geometry makes a difference.

I don't know what you mean by "reduce the number of nodes" as it sounds like you haven't meshed it yet. Anyway, creating a good mesh from a geometry such as a car is a complicated process, and there are no simple answers - I can only recommend for you to do the tutorials and do some CFX training.

You also mention wheel/ground interaction. Accurately modelling this effect is a difficult task. There are some research papers published describing studies of this effect, you will need to find them and do some reading.

As for whether it is better to import the geometry as surfaces or as points then recreate the geometry in Build - in my experience, Build tends to mesh surfaces generated in Build quite well, but surfaces imported from other packages sometimes cause problems. If it is possible to draw your geometry from imported points in Build I am sure you will find this the most effective way.

Regards, Glenn


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