197 Aerodynamics (CFD analysis)

Discussion in 'Clio 197 Area' started by tomislavp4, May 16, 2017.

  1. Zuban

    Zuban Paid Member

    39
    Renaultsport Clio 3 RS200
    I will need to go back over my setup and check, its been about a year since i did anything with it, and have since reorganised my lab setup, and managed to break my source ubuntu vm I set everything up on... but openfoam does seem to be good, but its not easy to use, and because my understanding of cfd is basic, its a vertical learning curve... I was using it really to see whether changes I made had the desired effect or not, positive or negative, and from that point of view it does the job.

    From memory whatever setup i had was memory limited, if you set the mesh detail too high then you wont get an error, you will just use more ram than the system has, and end up with the process using paging or swap file instead, and then your performance drops through the floor as instead of ram which is fast, part of your sim is being run from disk. So I always tune the setup to make sure its within physical memory.
     

  2. tomislavp4

    tomislavp4 Paid Member

    65
    Sweden
    Clio 197
    The simulation on the Sprint spoiler just got completed. It's effects are similar to those of the Cup pack but with lesser magnitude. It increases the drag by 12,3 percent and the lift by 31,1 percent so the improvement of the lift to drag ratio ends up being 16,5 percent.
    Skiss3.png
    Notice that I've added a column in the spreadsheet "fDF" as in "front downforce" which shows how big of a percentage of the total downforce acts on the front axle. The stock car has 60 percent of the downforce on the front axle while the Cup has 60 percent on the rear axle. The car with the Sprint spoiler has downforce that is evenly balanced between the axles. I've also added a Vmax column to show how how the changes affect the top speed. Values are in kilometers per hour so you might want to convert them to whatever you feel comfortable with.

    Here are velocity and low pressure plots on the symmetry plane for the Cup and the Sprint spoiler. Not much of a difference between the two other than the slight change in the wake. The Cup spoiler seems to be helping the diffuser suck a bit more air so the pressure in the diffuser area is lower on the Cup car, thus the difference in downforce. If I was to choose between the Cup and the Sprint spoiler based only on the results from these simulations I'd go with the Cup. It is more efficient at producing downforce which is what we want from a spoiler.
    Symmetry velocity.jpg
    Symmetry low pressure.jpg
     
    Sean197 likes this.
  3. tomislavp4

    tomislavp4 Paid Member

    65
    Sweden
    Clio 197
    Damn it. You can disregard the Sprint spoiler results for now. I'll have to run it again as I've used an older model with slightly different front bumper.
     
  4. petercronin

    petercronin Paid Member

    144
    North East England
    LY FF Clio 200 with Cup Pack
    I don't but from memory I think it was either in the official Renault sales brochure or it was something somebody from RUK stated on the renaultsport.com forum. I'm almost certain it said 40kg at 80mph though and yes I think it was referring to the diffuser.
     
  5. ///M

    ///M Gold Member

    RB R27#312 & an ///M
    Oh man, you got me all excited and then said to disregard it!

    :smiley:

    Noticed that the Cup model has the splitter too, would that affect other bits?

    As for your thoughts on a custom splitter, I'm looking at it exactly the same. You'll be an absolute HERO to me if you come up with something that works, looks good and could be made.

    I have a pretty solid idea for how I'd like it to look but my skills don't go any further than photoshop! But yeah, something more like that Porsche you posted would be so much better.
     
  6. tomislavp4

    tomislavp4 Paid Member

    65
    Sweden
    Clio 197
    Sorry mate, my bad!

    Yeah, the splitter should affect things so I ran a simulation on the Cup spoiler without the splitter to see how much of a difference it does make. Turns out it doesn't do much. So while the spoiler is functional, the splitter is all show and no go, at least according to these simulations. :tearsofjoy:

    Here are the values for all the simulations I've done thus far, including the sprint spoiler on the correct model. The Cup spoiler does have a slight edge when it comes to downforce and efficiency so if it's performance you're after, that one's for you. If you prefer the looks of the Sprint though, it's fine, you still get some increase in downforce and the reduction in top speed is lower compared to the Cup one.
    Skiss.png
    The pressure plots show how similar the Sprint and Cup spoilers are. They are nearly identical.
    Symmetry pressure.jpg
     
    Sean197 likes this.
  7. ///M

    ///M Gold Member

    RB R27#312 & an ///M
    Brilliant mate. I love how you can see the areas of pressure in the images. Very funny about the splitter. Are you running it at stock ride height for now? I'd be really interested to see if lowering it a lot made any difference to how effective (or not) the splitter and the diffuser are.

    I bet the side skirts don't do much either. They look good though!

    Most of all I'd love a proper splitter design on there though! Always had a feeling that splitter did nothing!
     
  8. tomislavp4

    tomislavp4 Paid Member

    65
    Sweden
    Clio 197
    Stock ride height for now. I do plan on doing som runs on lowered/raked models though so stay tuned. The side skirts don't do anything and I don't need CFD to tell me that!
     
    ///M likes this.
  9. ///M

    ///M Gold Member

    RB R27#312 & an ///M
    Yeah but in all the Renault marketing they showed how they helped the airflow and stuff...

    :smiley: :smiley: :smiley:
     
  10. Zuban

    Zuban Paid Member

    39
    Renaultsport Clio 3 RS200
    do you have a small gap between the cup spoiler and the rear bodywork? be interested to know how much effect that gap has, and how you can change it to alter the wings effect. I played around with this a little and noticed it had some effect, it interested me because the potential to alter the wing mounts is something that is achievable, I also played around a little with changes to the end plates, enlarging them downwards and backwards and that had some interesting effects on drag if I remember correctly.
     
    ///M likes this.
  11. tomislavp4

    tomislavp4 Paid Member

    65
    Sweden
    Clio 197
    Yes, there is a gap between the edge of the bodywork and the spoiler but since I do not actually have these things laying around and modell from pictures, I cannot guarantee the accuracy of the size of the gap. Increasing the size should make the thing act more as a wing and less as a spoiler, which should give more downforce because then you'll have an airfoil in free stream. What you say about the endplates makes sense, they should affect the drag coefficient. By enlarging them you effectively make the sides of the car longer which does reduce the wake and thus the drag.
     
    ///M and Zuban like this.

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