CFD and Aerodynamics Q

[Lusso]

Hi, how is everyone. Before i start, i just wanted to say what a wonderful site you guys have here. I am a long time reader (first time poster) and it is always a pleasure reading the forum topics on this site. Well done!!

Anyways to my question, well i actually have two, one on CFD and one on general aerodynamics:

Firstly, from what i have read, it is known that the better a car's aerodynamics are when it is running on its own, the more a car running behind it will be hampered. What i want to know is why is this so?? Because shouldn't an aerodynamically efficient car have a relatively laminar flow trailing it, whereas an aerodynamically inefficient car would have turbulent flow. And so wouldn't this mean the more efficient car wouldnt hamper the trailing car as much.

Secondly, i have just been starting to learn Gambit and have kinda run into a problem with a tutorial i am doing. It is the very first tutorial that i have done (ever) so its kinda annoying and i don't really know what's going on. The tutorial is at:

http://instruct1.cit.cornell.edu/course ... /step1.htm

and the problem i am having is on the very last step where it says:

"To create the face consisting of GAFEG+airfoil surface, select the edges in the following order: AG, AF, EF, EG, and JG, HJ, HI and IG (around the airfoil in the clockwise direction). Click Apply."

I cant seem to create this face in Gambit, i think its something to do with the airfoil and boundary having the same edge and not being able to create a face because of this.

If anyone could help me with the above it would be greatly appreciated.
By the way, if anyone out there has any recommended tutorials on Fluent/Gambit that, from experience, they have found quite handy could you please let me know.

Thanks, Lusso

[SoftBatch]

On your first question, think of F1 cars as more down force efficient than aero efficient. They have large wakes that disturb the other cars because they are using every last bit of the cars body to make down force with aerodynamic secondary.

When was the last time you heard of an 800hp car being limited to around 200mph?

[AeroGT3]

On your first question, think of F1 cars as more down force efficient than aero efficient. They have large wakes that disturb the other cars because they are using every last bit of the cars body to make down force with aerodynamic secondary.

When was the last time you heard of an 800hp car being limited to around 200mph?

Yes, F1 cars are terribly inefficient. An aircraft engineer would gasp at their Cd. However, for the downforce/wing loading they achieve, their Cd is quite respectable. It's all a matter of perspective. Bluff bodies typically don't provide outstanding efficiencies inherently.

[Cornell Racer#1]

WOW!! Good to see my school on this thread.......haha Lol!

Just outta curiosity, how did you manage to find this link?!?! Do you also go there?

[syguy]

If you haven't already, try posting your Gambit question to the Fluent forum on CFD-Online.

[kilcoo316]

Secondly, i have just been starting to learn Gambit and have kinda run into a problem with a tutorial i am doing. It is the very first tutorial that i have done (ever) so its kinda annoying and i don't really know what's going on. The tutorial is at:

http://instruct1.cit.cornell.edu/course ... /step1.htm

and the problem i am having is on the very last step where it says:

"To create the face consisting of GAFEG+airfoil surface, select the edges in the following order: AG, AF, EF, EG, and JG, HJ, HI and IG (around the airfoil in the clockwise direction). Click Apply."

I cant seem to create this face in Gambit, i think its something to do with the airfoil and boundary having the same edge and not being able to create a face because of this.

If anyone could help me with the above it would be greatly appreciated.
By the way, if anyone out there has any recommended tutorials on Fluent/Gambit that, from experience, they have found quite handy could you please let me know.

Thanks, Lusso

You cannot create the farfield face or the aerofoil face?

What error does it throw up? It could be you have two vertices at identical positions, and gambit thinks the lines are not connected.



Oh, and welcome to the wonderful world of gambit - if you have any hair on yer head - get a baseball cap - it'll stop you pulling it out

If you can, get ICEM, its a much more powerful tool.


edit: What you can do is create the domain face, and then the aerofoil face seperate - and subtract the aerofoil face from the domain face, you'll find the subtract function by right clicking on the third gui to the right of the create face from wireframe (the default thing is unite faces), right click brings up the other options.

[ginsu]

I have done that tutorial and get the exact same problem, I just downloaded the premade airfoil.

What is ICEM and why is it better than gambit? And does it export to Fluent directly?

[AeroGT3]

I have done that tutorial and get the exact same problem, I just downloaded the premade airfoil.

What is ICEM and why is it better than gambit? And does it export to Fluent directly?

Gambit just sucks. It isn't easy to use, its terribly slow, and it just isn't clear and simple. IMO Fluent can mesh adaptively better than gambit can period. Gambit can't even support simple meshing like Cartesian unstructured, as far as I know.

[kilcoo316]

What is ICEM and why is it better than gambit? And does it export to Fluent directly?

ICEM is another mesher, sold by the Ansys crowd (that bought Fluent Inc last year) - ICEM exports in many formats, fluent is one of them.

[Carlos]

CDF analysis of an F1 car design: section on sidepods is especially interesting

http://www.fluent.com/solutions/articles/ja075.pdf

[kilcoo316]

CDF analysis of an F1 car design: section on sidepods is especially interesting

http://www.fluent.com/solutions/articles/ja075.pdf

*snigger*

250K elements for the front end?


Who are they trying to kid?


I would love to see those compared to time averaged experimental pressure data - I'll bet the comparison would not have been published in no Fluent journal!

[miqi23]

True, 250K seems quite coarse and I think the front end shown there for sure has more cells assigned to it. Moreoever, the pressure profile looks alright in figure 10.

[kilcoo316]

True, 250K seems quite coarse and I think the front end shown there for sure has more cells assigned to it. Moreoever, the pressure profile looks alright in figure 10.

Here mate, no suspension elements in fig3... there are in fig 10

[miqi23]

Aha, I know what you mean there...

Why would some one do that?