Front Wing Vortex Breakdown

[Crucial_Xtreme]

Great article from Gordon I figured I'd share. Enjoy. Cheers.


Front Wing Vortex Breakdown

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With the assistance of Mercedes GP, Jacques Heyder-Bruckner completed a PhD thesis in 2011 which analysed the front wing-wheel interaction on a racing car. Of particular interest in this work is the fact that Detached Eddy Simulation (DES) was used to represent the phenomenon of vortex breakdown, which occurs when the front-wing approaches low ride-heights under conditions of roll and pitch.



Whilst Reynolds Averaged Navier-Stokes (RANS) simulations are the CFD workhorse of modern motorsport, RANS is known to be inadequate for representing separated flows, and in particular for representing large-scale vortical phenomena, such as vortex evolution and breakdown. In contrast, Detached Eddy Simulations use RANS to represent the attached flow, but directly solve the Navier-Stokes equations in the regions of separated flow.
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Q-criterion isosurfaces of the vortex breakdown phenomenon, taken from the instantaneous DES flowfield, are depicted here. Bruckner points out that “the vortex breakdown moves forward as the wing is moved closer to the ground…The large vortex expansion…is composed of a recirculation region enclosed by the spiralling tail shed from the vortex breakdown.This causes high pressure fluctuations on the endplate and flap, resulting in a more unstable wing with variations in downforce and drag three times larger than at higher ride-heights.” (p116).

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McCabism: Front Wing Vortex Breakdown

Jacques Heyder-Bruckner/Southhampton Paper Link

[Huntresa]

I dont rly understand the text but i can see the images and the changes, what is actually going on in laymans english ?

[CBeck113]

The lower the wing the higher the chance that the vortices will collapse (turbulent flow) which basically ruins the air flow for the rest of the car.

EDIT - spelling error

[Just_a_fan]

Which is why the teams put so much effort in to the wing endplate's design. The paper's wing and endplate are simple designs. It would be fascinating to see a current front wing analysed.

It should also be noted that the tyres are grooved rather than slicks.

[Richard]

Interesting to read about eddy simulation too, that seems to pop up often in PhDs on wind flow. I see he used Gridgen for meshing and Fluent for solving.

[bhall]

The lower the wing the higher the chance that the vortices will collapse (turbulent flow) which basically ruins the air flow for the rest of the car.

EDIT - spelling error

So how does (did) Red Bull make this work?

[Pup]

Possibly the added drag on the front wing is compensated for by a greater loss of drag at the back, since without the vortexes, the air is no longer interacting the same with the downstream bodywork? Just a guess.

Or perhaps clever wing design just allowed it to drop further before the vortexes began to break down.

[CBeck113]

I would say by Improving and increasing the flow directly into the low pressure area "behind" the profile. The slots allow air to pass through and the flow conditioners , well, do their job by maintaining laminary flow. Sacrificing this area with a very high pressure drop under the wing, which would normally be the goal of the wing, can only be done when the down force is generated elsewhere (i.e. winglets, multiple elements etc.).

I would really love to see the actual vortice "plan" from the RB9, AN seems to sacrifice cw just to generate the right vortices to seal the diffusor / exhaust / floor - must be a work of art.

http://www.racecar-engineering.com/wp-c ... prb9rw.jpg

[Pup]

Also, there's some homeostasis built in, since as the wing drops, downforce decreases; i.e., the wing will only drop so much. The RB may have been designed to work well on the limit of complete vortex breakdown.

Probably a good example of things going not so well in this respect would be the current McLaren.

[Kiril Varbanov]

The lower the wing the higher the chance that the vortices will collapse (turbulent flow) which basically ruins the air flow for the rest of the car.

EDIT - spelling error

So how does (did) Red Bull make this work?

http://www.shrani.si/f/1K/8K/4KqXWDMl/redbull1.jpg

Nice that the author has also used PIV to double-check and prove the work of DES.

I think he has used a low-speed simulation, but I will have to read the entire article, which might be the explanation. There's quite a lot of data to be cross-checked.

@bhallg2k - it's not only Red Bull, lots of teams are having similar solutions, and the front ride height is not that much different. In the Red Bull's case it's mostly down to sufficient rake, as opposed to lots of drag or broken airflow.
Let's not forget that Red Bull's front wing is having all these multiple vortex generators / deltoid wings and the wing itself is made to produce laminar flow as much as possible.

Still, to be sure, we will have to look at the actual CFD for the wing

[shelly]

The lower the wing the higher the chance that the vortices will collapse (turbulent flow) which basically ruins the air flow for the rest of the car.

EDIT - spelling error

So how does (did) Red Bull make this work?

http://www.shrani.si/f/1K/8K/4KqXWDMl/redbull1.jpg

the work is based on 2008 regs (high narrow front wing) - a really different situation. With current regs, the two main endplate vortices run on the outside of the front wheel, instead than on the inside as it was in 2008 and as it is dicussed in the thesis.
Fantastic document to discuss

[AnthonyG]

In the simulation the wheel looks like a full wheel (like the disks from a few years ago) wouldn't that make a difference compared to a "real" wheel?

[GitanesBlondes]

What would have happened with the vortex if the front wing had been angled so the airflow moved from down to top as it passed over the wing?

[CBeck113]

In the simulation the wheel looks like a full wheel (like the disks from a few years ago) wouldn't that make a difference compared to a "real" wheel?

Yes, especially since his wheel is not rotating. His goal, as far as I can see, was just to see what happens under/behind the front wing when the height is changed, so he could leave this interaction out. The teams don't have this luxury.
I will download the paper (finally!) when I get home and see what other gems are hidden in there.

[aussiegman]

The lower the wing the higher the chance that the vortices will collapse (turbulent flow) which basically ruins the air flow for the rest of the car.

Ground effect may possibly have some benefit in this as well as the high rake angles.

From McCabism:

Red Bull, McLaren and Ferrari currently appear to be converging on the same aerodynamic solution: a high-rake, nose-down stance to maximise the ground effect component of front-wing downforce, (with the use of exhaust-blown diffusers to retain rear downforce).

The principal point is that front-wing ground-effect depends upon two mechanisms: firstly, as the wing gets closer to the ground, a type of venturi effect occurs, accelerating the air between the ground and the wing to generate greater downforce. But in addition, a vortex forms underneath the end of the wing, close to the junction between the wing and the endplate, and this both produces downforce and keeps the boundary layer of the wing attached at a higher angle-of-attack.