Lotus E20 VD

[Cam]

Isn't air and fluid treated the same? It's just the density that makes the difference?

http://en.wikipedia.org/wiki/Drag_(physics)

[Dragonfly]

Perhaps you meant 'liquid' because both are fluids, but air is a gas.

[gato azul]

Isn't air and fluid treated the same? It's just the density that makes the difference?

http://en.wikipedia.org/wiki/Drag_(physics)

As dragon fly said both are fluids, and fluid dynamics deal with both liquids and gases, the same principles apply, but the
key difference is the compressibility of the fluid in question.
Air for the speeds covered by F1is considered incompressible, but for other gases and/or at higher speeds this needs to
be taken into account.
Some flow testing for cars (even race cars in the past) is/was done in "water tunnels"



video link

Due to the different densities of the fluids, the speed/velocity of the tests needs to be adjusted to achieve the desired results ( Re number etc.)

To make it clear, I do not want to mess with anybody's mind.
I just feel that we will struggle to 100% explain what happens only with 2D lift/drag theory (infinite wing span), therefore in think induced drag needs to be understood and considered a bit as well.

Which means looking a bit at farfield drag and the Trefftz plane concept (there are other Munks Stagger Theorem etc.)
, at least trying to understand the concept of lift induced drag.

But maybe all this is beyond the scope of this forum, if so - apologies, I will not "drag" on with it.

[rjsa]

@gato azul, I read waves in the first diagram as surface effects on water surface going vessels. The second one is pretty clear when it mentions shockwaves and mach 1+ flow. It that's not it then I'm sorry.


@cam, boats deal with the water free surface and displacement waves that are a major factor on drag. Yes, most of the equations are the same, you just switch the density value, but free surface effects (waves) are not experienced by cars or airplanes.

Ohh, just seen gato azul's last post: When it comes to scale testing hell breaks loose, everything works backwards scale-wise and like he showed, sometimes water is better testing air than air itself. Or you just stick sanding paper to sections of your seagoing hull model to make the results reasonable.

@ gato azul: ITA?

[gato azul]

@rjsa
all good mate - no worries

ITA? = Italy? if yes, then no

[rjsa]

@rjsa
all good mate - no worries

ITA? = Italy? if yes, then no

Like in the aeronautical engineering school. The nickname suggests BR and the content aeronautica engineer.

[gato azul]

@ rjsa

o.k. gotcha now - but no neither, I have some exposure to this stuff, but don't hold a academic degree in aeronautics or study it.

as for our "drag" issue, maybe this site does a good job to explain some basics, without being to technical/academic
momentum theory of lift



keep in mind, that these are concepts/theories to explain and help to calculate things, not necessary 100% true representations of reality.

for a race car application, you would/could call ɛ "upwash" angle and need to mirror the graphic along the horizontal axis.
Lift = Downforce I Downwash angle = Upwash angle

[PlatinumZealot]

My faith in f1 technicaL has dropped emensly. ... is just making the site boring for me..

Your're not happy. If you're not happy, leave. Don't whinge and complain about it not being what you want. If you want 'your vision', go start your own forum.

• Not everyone knows other sites exist - hence people link to them
• Quoting journo's and news sources is relevant - even if they're wrong
• Like all mining, you must sift the muck to find the gold
• A wrong post can be valuable if people learn from it

F1 Technical is, for intents, the best online free source for F1 technology, science and discussion on all related things. It's not perfect. But it is a very valuable source of information and 'directory' to external resources.

Take the good with the bad and help move it forward. The world wants solutions, not complaints.

*apologies for the off topic, but really, whingers get me revved.

Yes. I like whinging. You need whingers like me. And I will continue to post in here because as I said, some posts are very interesting. I have a small preview for you guys...

I have to try work things out behind the scenes...

No slots:



You can see the cross section of the pylon is not shaped properly (too round). I will have to change it to a more teardrop shape. The Side profile of the Pylon is differernt from the real thing, but that is OK for this calculation. the reason the Lotus one is "S" shaped is to help reduce flow losses from the inlets, I don't have to model this part as I can choose my mass flow rate out of the slots in the pylon.


Slots:




There are a few nuances that cause me not to get conclusive results.
Some fine details have to be sorted out before the model is even close to being accurate.
All my slots are doing are reducing down-force but the drag barely drops.
This particular attempt just makes the wing flat out worse.
So it is a tricky system to set up, I have to keep refining it to get it right.. I am expecting either a significant drop in drag OR a significant increase in down-force. I think it would be one of those two options for Lotus.

[gato azul]

nice work n smikle
how much does the downforce drop in your model/simulation?

[amc]

I don't like to rubbish the theory n_smilke, as there's clearly a lot of work gone into this. However, have you considered directing the flow backwards? I posted a figure earlier that this reduces about 8-12% of the rear wing's total drag, which is a fairly minimal amount, indicating the VD only works on a very small amount of the wing.

Looking at the CFD, I can tell you why downforce drops and drag doesn't. High pressure air is being pumped straight into a low pressure region necessary for downforce, and with a lower pressure delta there is gong to be less force. Drag isn't reduced much because air is actually pulled back towards the wing to fill the area behind the pylon, which is now vacant of any flow from in front of the wing. Just look at the arrows - they show that air from in front of the wing is moving away from that area, and air behind the wing is being pulled downwards. The low pressure behind the pylon is actually bigger in the third diagram, causing more drag.

Just try pointing the slots backwards and putting flow directly behind the pylon. The low pressure peaks will be untouched, but the arrows that point downwards behind the pylon in the first picture will suddenly point upwards. Faster flow behind the wing means less drag.

Stalling a wing, in the sense that the boundary layer separates, is not an effective way of reducing drag. It becomes very unpredictable and isn't generally a good thing. In this sense VD, F-ducts and DDRS don't stall their respective wings. Stalling an aircraft wing is not directly to do with speed, slots, blown slots, camber etc. but angle of attack, which increases as the plane slows due to the CoP movement away from the CoG. In fact, DRS doesn't stall the wing either - it just reduces drag and downforce proportionally.

VD, F-duct and DDRS all reduce drag on a wing, and the reason it is mistakenly called 'stalling' is that the amount of downforce produced drops. But that's not really what stalling means. I would like to steer clear of 'stalling' talk as this is a confusing term which can have many different meanings. If an F1 wing were to truly stall at any speed there would be serious problems. It would have a similar effect to Hakkinen's crash at Hockenheim where the rear wing simply broke off. To be avoided.

[Tommy Cookers]

Stalling a wing, in the sense that the boundary layer separates, is not an effective way of reducing drag. It becomes very unpredictable and isn't generally a good thing. In this sense VD, F-ducts and DDRS don't stall their respective wings. Stalling an aircraft wing is not directly to do with speed, slots, blown slots, camber etc. but angle of attack, which increases as the plane slows due to the CoP movement away from the CoG. In fact, DRS doesn't stall the wing either - it just reduces drag and downforce proportionally.

VD, F-duct and DDRS all reduce drag on a wing, and the reason it is mistakenly called 'stalling' is that the amount of downforce produced drops. But that's not really what stalling means. I would like to steer clear of 'stalling' talk as this is a confusing term which can have many different meanings. If an F1 wing were to truly stall at any speed there would be serious problems. It would have a similar effect to Hakkinen's crash at Hockenheim where the rear wing simply broke off. To be avoided.

well said !!

(BTW detail, the aircraft largely maintains AoA unless forced by the pilot)

[superdread]

Stalling a wing, in the sense that the boundary layer separates, is not an effective way of reducing drag. It becomes very unpredictable and isn't generally a good thing. In this sense VD, F-ducts and DDRS don't stall their respective wings. Stalling an aircraft wing is not directly to do with speed, slots, blown slots, camber etc. but angle of attack, which increases as the plane slows due to the CoP movement away from the CoG. In fact, DRS doesn't stall the wing either - it just reduces drag and downforce proportionally.

It may not be effective in an aircraft but it is in a car. Stalling of an aircraft wing has certainly to do with wing profile, speed, ... and not only AoA, that's why large transport aircraft are extremely prone to stalling compared to a propeller fighter. Also as stalling an aircraft wing is a continuous process there is a level of unpredictability (small factors can decide if stalled/not stalled), but the systems we see on cars are binary (if off the wing has a very good flow attachment and if on the flow is well detached). Especially the steepest part of the wing is easy to stall (the F-Ducts went for that area, and the Lotus system reaches maximum wake width there).


In the first DRS-year some teams had issues with reattaching the flow (the flaps were too steep to gain the maximal top speed gain) but by now they compromised drag reduction for fast reattachment (because they use DRS mainly in qualifying). (The DRS doesn't stall the wing in a strict way, in a sense it stalls itself when closing and the flow has to reattach to it.)

[PlatinumZealot]

I don't like to rubbish the theory n_smilke, as there's clearly a lot of work gone into this. However, have you considered directing the flow backwards? I posted a figure earlier that this reduces about 8-12% of the rear wing's total drag, which is a fairly minimal amount, indicating the VD only works on a very small amount of the wing.

Looking at the CFD, I can tell you why downforce drops and drag doesn't. High pressure air is being pumped straight into a low pressure region necessary for downforce, and with a lower pressure delta there is gong to be less force. Drag isn't reduced much because air is actually pulled back towards the wing to fill the area behind the pylon, which is now vacant of any flow from in front of the wing. Just look at the arrows - they show that air from in front of the wing is moving away from that area, and air behind the wing is being pulled downwards. The low pressure behind the pylon is actually bigger in the third diagram, causing more drag.

Just try pointing the slots backwards and putting flow directly behind the pylon. The low pressure peaks will be untouched, but the arrows that point downwards behind the pylon in the first picture will suddenly point upwards. Faster flow behind the wing means less drag.

Stalling a wing, in the sense that the boundary layer separates, is not an effective way of reducing drag. It becomes very unpredictable and isn't generally a good thing. In this sense VD, F-ducts and DDRS don't stall their respective wings. Stalling an aircraft wing is not directly to do with speed, slots, blown slots, camber etc. but angle of attack, which increases as the plane slows due to the CoP movement away from the CoG. In fact, DRS doesn't stall the wing either - it just reduces drag and downforce proportionally.

VD, F-duct and DDRS all reduce drag on a wing, and the reason it is mistakenly called 'stalling' is that the amount of downforce produced drops. But that's not really what stalling means. I would like to steer clear of 'stalling' talk as this is a confusing term which can have many different meanings. If an F1 wing were to truly stall at any speed there would be serious problems. It would have a similar effect to Hakkinen's crash at Hockenheim where the rear wing simply broke off. To be avoided.

You would be surprised If I told you they are pointing backwards.. about 30 degrees. The low suction peak under the wing sucks the air sideways. This is not the final model though.

Yes those reasons are why.
Downforce drops by 13% but the drag doesn't drop significatnly.. As I said the wing is not made right. I didn't intentionally set out to stall thew wing. So these are not valid.

[gato azul]

Downforce drops by 13% but the drag doesn't drop significatnly..

Thanks for the answer n smikle,
how does your model/program/software access/define/calculate drag?

[hardingfv32]

n smikle

Why does the end plate seem so affected by slot activation?

Why is the end plate not solid?

Thanks, Brian