Newey on the aerodynamic effect of Monaco’s tunnel

[krtekf1]

I watched the FIA review of season 1995 recently and found an interesting short interview with Adrian Newey at Monaco GP (at that time he was still at Williams team). He spoke about effect that the roof of the tunnel has on the aerodynamics of the car: “The tunnel is particulary interesting case actually, because the tunnel, you have a roof that affects the aerodynamics of the car,… (I dont understand few words)… rear wing is deflected by the tunnel roof and it actually causes a special problem because you tend to lose rear downforce in the tunnel…it is flat, but not comfortable flat for the drivers.”

I still dont understand how tunnel affects on the aerodynamic !?. Does anyone have a logical physical explanation?

I posted the same thing at f1fanatic.com/forum, but I didnt really understand the answers...

(http://www.f1fanatic.co.uk/groups/f1/fo ... in-monaco/)

[wesley123]

The wing pushes the airflow up, this pushes the car down. Because there is a roof, this airflow cant flow up as much as in a open world as it is blocked. Therefore there is less downforce.



There obviously is more to it, but i do not think it can be explained any easier

[olefud]

The wing pushes the airflow up, this pushes the car down. Because there is a roof, this airflow cant flow up as much as in a open world as it is blocked. Therefore there is less downforce.

http://i.imgur.com/LkzYrTB.png

There obviously is more to it, but i do not think it can be explained any easier

Seems like the tunnel would have a “ground effect” mechanism that would increase the downforce. This can be thought of as providing something solid for the updraft to push against. Or, it can be thought of as increasing the pressure between the tunnel surface and the wing and thus the pressure on top of the wing. The endplates on the wing seemingly would already confine the vortices, but, if they didn’t, the tunnel roof would also diminish this loss of downforce.

[Tommy Cookers]

IMO the tunnel is making the wing act as if its AoA had been reduced

this is the constraint effect, to avoid such errors a wind tunnel model must be suitably small relative to the tunnel size
how small is suitably small is a perennial question, since we want the model to be as large as possible to avoid other errors

the Jaguar F1 car was rubbish aerowise because the tunel testing they were contractually bound to (in another country) used a tunnel that was too small for the model (as often happens eg for reasons of tunnel costs)
in the tunnel the wing worked fine at 13 deg AoA, on track the wing stalled at 13 deg (ask Mr Irvine)
I have no confidentiality obligation in this case

[autogyro]

Surely the cars develop more downforce in the Monaco tunnel and this accounts for so many of them loseing DF exiting the tunnel and spinning.
Could just be the bump though.

[mep]

I would say the roof can restrict the air from moving up and essentially creating a increased pressure above the wing. This could load the top surface of the wing slightly more but I doubt this is noticeable. It will rather cause the flow on the lower surface to detach (wing stall), causing a significant reduction of downforce.

Edit: Testing the rear wing in a windtunnel is generally rather inaccurate because these wings are so sensible and close to stall that the results of a scaled model does not necessary correspond to reality.

[autogyro]

Could the car force air ahead of it through the tunnel?
This would create turbulance at the tunnel exit.

[SectorOne]

Is it not exactly the same effect of a DRS only larger and less effective?
Correct me if i´m wrong but the DRS essentially deflects the airstream below the rear wing more horizontally right?
If yes then it would be the same type of effect only that it´s happening much higher up and less effective?

[godlameroso]

Close, the truth is any enclosed area will disrupt the wake of the car, once the car cuts through the air, the resulting way that air rushes to fill that void is what causes downforce. To be honest the Armco barriers also work to disrupt downforce, because the wake of the car isn't just limited to the vertical, a lot of work goes into conditioning air that is traveling laterally as well. F1 aero also has to deal with aero consistency in yaw conditions.

[olefud]

Could the car force air ahead of it through the tunnel?
This would create turbulance at the tunnel exit.

If the car were moving through the tunnel it would. If you stand at a railroad tunnel exit you can feel the air being pushed by an approaching train. But the car in a wind tunnel isn’t moving so it builds static pressure ahead of it.

http://en.wikipedia.org/wiki/Ground_effect_(aircraft)while inverted might be of interest.

[xpensive]

Perhaps related, I read somewhere that a train travels easier through a tunnel than in open air, but I never got an xplanarion?

[hollus]

Less air to push forward in the tunnel than in the open, I guess. Either you interpret this directly as less drag or conclude that the air around the train will be more "pre-accelerated" while in the tunnel and hence of a lower relative velocity to the train (this must be a small effect for an F1, but certainly would reduce downforce). Either way, less momentum transferred to the external air.

[mep]

I think you have read something wrong there. It does not seem to make sense and some quick google search confirmed this. A train in a tunnel is like a piston. The air column in front of the train has to be pushed through the tunnel while the gap behind the train still has to be filled. The flow around the train has to pass through a restricted area between train and tunnel walls and therefore has to flow much quicker. A high mass of air is moved through the tunnel consuming energy.

[CBeck113]

mep's right - the tunnel causes the pressure difference between the front and rear of the train to grow, since the air can only come from the two openings of the tunnel. And delta p is basically cw, so you ruin the aerodynamic effency with the tunnel. Like when drinking through a straw - pressure on the fluid side is higher, in your mouth you create lower pressure, and the fluid flows to the lower pressure side.
Although I don't think that the effect on the car in the tunnel is very extreme, I do believe that this is the primary reason for not allowing DRD to be used in it; having such low pressure already will make the rear very nervous.

[Tommy Cookers]

in Japan (I think) they now have some lines where each track has its individual tunnel, and the train is a close fit in its tunnel
the tunnel needs and has at each end a silencing structure like the silencer on a gun barrel
otherwise there is a big bang