Under floor flow & diffusers

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chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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We can see the pattern as observed on the redbull and ferrari in austin of a twisting and bending vortex

Image

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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Do your work and disappear !

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Abracadabra !

shelly
shelly
136
Joined: 05 May 2009, 12:18

Re: Under floor flow & diffusers

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In your last image following the path of the vortex tube form left to rightyou can see how the vorticity decreases form blue to green going away from the source and then as the vortex is stretched to go under the surface the vorticity is increased (blue again), That's the effect of vortex acceleration- vortex stretching
twitter: @armchair_aero

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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That's right! I choose the right color panel and transparency to illustrate, those software are great !

MadMatt
MadMatt
125
Joined: 08 Jan 2011, 16:04

Re: Under floor flow & diffusers

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I like that simulation with the bird, good flow behavior is captured!

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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Thanks! I'm the vincent van Gogh of cfd rendering :lol:

http://oi62.tinypic.com/1z3osbn.jpg

http://oi58.tinypic.com/fxnpz.jpg

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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I'm still trying to investigate flow behavior around an f1 car.
I found out that vortices appear quit "naturally" just from basic fia imposed geometry plus rake. For example outer front floor corner and T-tray corner generate vortices with rake because of, well let's quote Flash Gordon Mccabe on this one :

"The crucial point is that this lateral pressure gradient corresponds to the creation of a spanwise-gradient in the streamwise velocity ∂U/∂z > 0. To see why this is crucial, however, we need to look at the Vorticity Transport Equation (VTE) for ωx , the streamwise component of vorticity.
The effect in question can be seen by studying incompressible, inviscid, laminar flow, so we can simplify the VTE by omitting the turbulent and viscous terms to obtain:

Dωx /Dt = ωx (∂U/∂x) + ωy (∂U/∂y) + ωz (∂U/∂z)

The left-hand side here, Dωx /Dt, is the material derivative of the x-component of vorticity; it denotes the change of ωx in material fluid elements convected downstream by the flow. Now, we started with ωz > 0 in the boundary layer, and by virtue of creating a lateral pressure gradient, we also have ∂U/∂z > 0. This means that the third term on the right-hand side in the equation above is positive, which (assuming the other pair of terms are non-negative) entails that Dω x /Dt >
0.
Thus, the creation of the spanwise-gradient in the streamwise velocity ∂U/∂z, skews the initially spanwise vortex lines ωz until they possess a significant component ωx in a streamwise direction. The lateral pressure gradient has created streamwise vorticity."

Where x,U are streamwise and z,W spanwise in the VTE.

So that is the picture i get from a basic geometry without wings :

Image

Image

So F1 engineers create some vortices but control others that are inevitable and potentially bad. I observed upper sidepod vortices on this redbull style design that seems to indicate the purpose of the sidepod winglet that deviate the flow laterally. So i investigated further...

And created those winglet and as expected it seems to control and reinforce sidepod vortices which goes back just under the rear wing main plate at the center.

Without winglet :
Image

With :
Image

I like F1 aerodynamic!

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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RedBull on fire !

Image

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variante
133
Joined: 09 Apr 2012, 11:36
Location: Monza

Re: Under floor flow & diffusers

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chuckdanny, the sidepod vortices you are talking about wouldn't exist on an actual F1 model. Your vortices are created thanks to the sharp (or almost) edges of the sidepods, which put in direct and "violent" contact (or almost...) two areas characterized by different pressures: upper and lateral side of the pods. If you apply the mandatory 75mm radius to the bodywork, the transition between the two areas will become much smoother and those vortices will disappear.

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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Really ? I choose 90 mm ! Well it reduces to 10 but very far back.
That's a shame it's so cool for the show! they could use color smoke for qualifying like aerobatics aircraft teams to improve whouah effect ! :o

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variante
133
Joined: 09 Apr 2012, 11:36
Location: Monza

Re: Under floor flow & diffusers

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90mm radius? mmh... Not on the transition areas...
Anyway, no, those vortices won't form on an accurate model.

You know what's cool for the show? All the vortices coming from the aero appendices that on your CAD model are missing :)
You've got a powerful software under your hands (with really impressive post processing tools), so why don't you try to simulate a complete and accurate F1 model? It'll take time, but it will be worth!

For example, you may take this as your archetype (god bless Sauber for this image [-o< )
Image

Also, it would be interesting to see how the Mercedes batwings actually perform on a complete (even if semplified) environment.

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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I just found how redbull could achieve same level of downforce with slim rear wing and you are jealous hmm ?

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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Is it this picture that give you this confidence that no, absolutly no these sidepod vortices don't exist ?

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variante
133
Joined: 09 Apr 2012, 11:36
Location: Monza

Re: Under floor flow & diffusers

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chuckdanny wrote:Is it this picture that give you this confidence that no, absolutly no these sidepod vortices don't exist ?
Not only this picture. Actually, i've run several CFD simulation of complete F1 cars designed by me (here are some images: http://www.f1technical.net/forum/viewto ... 1&start=45)
I have to say that the softwares i've used were running with the "k-epsilon turbulence model" (and standard environment settings), which is quite gentle when it comes to flow separation. Still, that's a reliable model and i don't see the extremes for the formation of the previously cited vortices anyway.
chuckdanny wrote:you are jealous hmm ?
oh yes, i'm jealous of your software with that awesome post processing tool! :D

chuckdanny
chuckdanny
69
Joined: 11 Feb 2012, 11:04

Re: Under floor flow & diffusers

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great! nice work, i use realizable k epsilon also with a 2 layer of 2nd order convection scheme (shear-driven) with a two layer all y+ wall treatment with a coupled flow solver and of course it's a RANS(reynolds averaged navier stokes) model :mrgreen: .

I can't reasonably go higher than 2 million cells but i have great control of the trimmer mesh, of course prism layer for boundary layer, i can refine based on any quantity of interest, turbulent kinetic energy, streamwise vorticity etc...
I'm just discovering all these things so it's just exploration for the moment to better understand key areas from second order refinement ones.