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Downforce for sports car at wheels

Question asked by 1-QNZQMT on Jul 21, 2010
Latest reply on Sep 27, 2010 by 1-6FGS9O

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Hi Everyone,

I need some advice on how to calculate downforce on a sports car.

My objective is to simulate a car without spoiler/rear wing vs a car with spoiler/rear wing.

I want to calculate downforce at the front wheels vs rear wheels. I made a slight cut at the bottom of wheels to simulate road contact.

Q1. Is it proper to put surface goals at those areas? (Surface goal component force Y)

Q2. Any other ideas to measure downforce more efficently?

Q3. External flow, or internal flow (design a tunnel and place the car model in it). Which is better?

Appreciate if help/advise can be contributed coz I need these answers ASAP

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Zul CAR with rear wing.SLDPRT.zip1.4 MB

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1-E9V5A2 Jul 21, 2010 5:24 AM

Hello,

Yes, put surface goals anywhere and everywhere you want to know anything. It doesn't significantly increase solving time and lets you make the results plots you want.

I would recommend external flow for this simulation since the box walls will induce fluid friction if you put the car in a box and use internal flow. Then again, wind tunnels are basically boxes - I guess you just make the walls far enough away from the model that they don't have a significant effect on the results. I would then recommend you to try both and let us know what the difference is.

Remember to make use of symmetry if possible. Usually the left/right sides of a car are the same (pretty much)? This will cut calculation time by about 1/4.

Regards,

David Fletcher

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1-QNZQMT @ 1-E9V5A2 on Jul 22, 2010 3:36 AM

Ok... But what kind of value should I expect?

The model i made made no much difference of downforce values at rear tyres with or without rear wing

Plus do i need to model a floor (to simulate road surface) ?

Any other criteria to make the simulation more reallistic? coz i know my model is quite too simple

i have yet to perfected my skills to draw a car model.

for reference i have attached a .ppt on what i did so far and results I obtained. I dont think result make sence.

Attachments

downforce analysis.pptx530.3 KB
Zul Sport Car.SLDPRT.zip730.7 KB

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1-6FGS9O @ 1-QNZQMT on Sep 27, 2010 11:52 AM

Hi.

The low Value of your Force might be, because you scaled your car down.

I cannot open your file, since i'm on 2009.

If so, you need to multiply the force by the scale-factor you used in your model.

the floor is important because you have a diffussor at the car end on the floor, the effect of the diffusor should be bigger than the big wing.

I would suggest you put in a simple solid body floor, to get the diffussor activated(->ground effects).

if you look from the side, the free air at the back is bigger - if the car moves forward, at this point it generates some underpressure wich results in a downforce.

Rhight now,

your car has much more pressure at the front axle because the hood,and windshield acts like a huge downforcing wing.

without a rear wing your car could be lifted up at the rear axle.

.....thoughts of engineering

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3 Replies

1-E9V5A2 Jul 21, 2010 5:24 AM
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Correct Answer
Hello,

Yes, put surface goals anywhere and everywhere you want to know anything. It doesn't significantly increase solving time and lets you make the results plots you want.

I would recommend external flow for this simulation since the box walls will induce fluid friction if you put the car in a box and use internal flow. Then again, wind tunnels are basically boxes - I guess you just make the walls far enough away from the model that they don't have a significant effect on the results. I would then recommend you to try both and let us know what the difference is.

Remember to make use of symmetry if possible. Usually the left/right sides of a car are the same (pretty much)? This will cut calculation time by about 1/4.

Regards,
David Fletcher
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- 1-QNZQMT @ 1-E9V5A2 on Jul 22, 2010 3:36 AM
  Mark Correct
  Correct Answer
  Ok... But what kind of value should I expect?
  
  The model i made made no much difference of downforce values at rear tyres with or without rear wing
  
  Plus do i need to model a floor (to simulate road surface) ?
  
  Any other criteria to make the simulation more reallistic? coz i know my model is quite too simple
  
  i have yet to perfected my skills to draw a car model.
  
  for reference i have attached a .ppt on what i did so far and results I obtained. I dont think result make sence.
  Attachments
  - downforce analysis.pptx530.3 KB
  - Zul Sport Car.SLDPRT.zip730.7 KB
  Like • Show 0 Likes0
  Actions
  - 1-6FGS9O @ 1-QNZQMT on Sep 27, 2010 11:52 AM
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    Correct Answer
    Hi.
    
    The low Value of your Force might be, because you scaled your car down.
    I cannot open your file, since i'm on 2009.
    If so, you need to multiply the force by the scale-factor you used in your model.
    
    the floor is important because you have a diffussor at the car end on the floor, the effect of the diffusor should be bigger than the big wing.
    I would suggest you put in a simple solid body floor, to get the diffussor activated(->ground effects).
    if you look from the side, the free air at the back is bigger - if the car moves forward, at this point it generates some underpressure wich results in a downforce.
    
    Rhight now,
    your car has much more pressure at the front axle because the hood,and windshield acts like a huge downforcing wing.
    without a rear wing your car could be lifted up at the rear axle.
    
    .....thoughts of engineering
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Downforce for sports car at wheels

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