Undertray Design - CFD

[Coondason]

Hello,

In the last few months I'm trying to gather some info about Undertray Design and i have a few problems.

1. Can you please point me out to some relevant literature?
2. Which CFD would you prefer? (COMSOL/Solid FlowSimulation/Fluent)

Thank you

[Lorenzo Pessa]

The most popular book is from Joseph Katz, "Race Car Aerodynamics: Designing for Speed"

I've seen in the last "Bernuolli" (h t t p ://www.racetechmag.com/) there is an article about F1 undertray (I haven't read it yet!). F1 is a little bit too fast for Formula SAE.

Have a look at "Aerodynamics for Formula SAE: A Numerical, Wind Tunnel and On-Track Study"
h t t p ://papers.sae.org/2006-01-0808/

Evaluate well how can you get from your underbody in term of lift, drag and weight!

About CFD solver I use StarCCM+. Fluent is also a very good choice. I don't thrust very much on "CAD 3D" solvers: if you need CFD, use a CFD program.

For grid generation I use Ansa, a very powerful mesher with an user "enemy" interface.

[Coondason]

Hello,

first of all:

For grid generation I use Ansa, a very powerful mesher with an user "enemy" interface - LOL.

I know and read the books you mentioned, but i'm having a problem with getting information on how to define the problem properly, using CFD.

[Giant]

I have been using Star-CCM+ for 2+ years.

Use a full car model to evaulate the performance of your UT. Rotating tyres, moving ground, freestream and everything.

Make sure your full car model is very simple otherwise youre going to be spending a lot of time on the mesh.

For a full car simulation, you also need quite a bit of computing power...or a lot of patience.

[Lorenzo Pessa]

Originally posted by Giant:
I have been using Star-CCM+ for 2+ years.

Use a full car model to evaulate the performance of your UT. Rotating tyres, moving ground, freestream and everything.

Make sure your full car model is very simple otherwise youre going to be spending a lot of time on the mesh.

For a full car simulation, you also need quite a bit of computing power...or a lot of patience.

A full half car for a car at 0° of steering.
A full car in steering attitude (maybe on a skid-pad steering).

I would be very interesting to compare a simple car without aero devices with a simple car with aero devices. And it would be really interesting for example if you can run you real car with and without undertray in a skidpad test and compare timing.

[Jay Lawrence]

Keep in mind that the average speed on track is around 50km/h and the maximum speed on a skidpad is around 48km/h (assuming 2g sustained). Personally i have doubts about whether an undertray could perform effectively at such low speeds, especially on a skidpad where the car should be at a decent roll angle. No, i have no evidence to support this...

[Lorenzo Pessa]

Originally posted by Jay Lawrence:
No, i have no evidence to support this...

As the 99% of people speaking about aero in FSAE :-)

I want to look at data.

Let me grid. Let me grid.

[Coondason]

Jay,

Most people who havn't really looked into this field believe that aerodynamics don't affect the car so much.
But, studies that were made on cars with aero packages state without a doubt that it does make a difference.

[Demon Of Speed]

Build model, put in wind tunnel.

[Mehul Botadra]

Especially with the ground clearance rule gone, its just proves too much of an advantage since you'll be controlling major air flow from above the car. So wings could make a difference. But I'd still have my doubts.

I think the guys from Delft and MRacing in FSG didnt really pay attention to Aero, not that much. They'd done a preliminary analysis.