### Newey on the aerodynamic effect of Monaco’s tunnel (10 posts)

Topic tags: Monaco, newey
• krtekf1 said 4 months, 2 weeks ago:

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?

• George said 4 months, 2 weeks ago:

I would guess it increases the air pressure above the rear wing so the air moves off the wing slower? I’m not sure how that would affect the air flow, maybe it restricts the amount of air the wing can direct upwards. I’m not an aerodynamacist but all the air coming off the rear wing has to go somewhere, and usually it dissipates in like a 5m area above the car, if you block off that 5m then it stands to reason either it will compress or it will move out in other directions (which wont provide downforce).

• andae23 said 4 months, 2 weeks ago:

In simple terms: basically, the rear wing deflects the air upwards, which pushes the car downwards, thus creating downforce (action=reaction). With a roof, the air can’t be deflected as ‘high’ as without a roof, so effectively less energy is put into deflecting the air stream. As a result, less energy is put in pushing the rear wing down, so there is less downforce.

Little bit more difficult: the deflected stream of air ‘meets’ the horizontal stream that travels along the ceiling of the tunnel (frame of reference: the car is stationary and the air is moving), so the stream coming from the car is deflected. Because the air is travelling slower than the speed of sound, the information of this clash of airstreams ‘travels’ upstream towards the rear wing, which alters the pressures: the pressure difference between the upper and lower side of the wing decreases, which in turn decreases the downforce (and lift-induced drag).

The effect of a roof can be quite big: wind tunnel data (which of course also has walls) has to be corrected.

• Mclaren said 4 months, 2 weeks ago:

Surely the fact that there is less air in the tunnel will have an effect

• andae23 said 4 months, 2 weeks ago:

How is there less air in the tunnel?

• pH said 4 months, 2 weeks ago:

I find this puzzling. In aviation there is something known as the ground effect. The wing pushes the air down, thereby lifting the plane. If the plane is near the earth, the air has less room to go, so it starts “pushing back”, lifting the airplane even more than normal. This makes life difficult for novice pilots, they line up nicely to arrive near the beginning of a runway, gliding down at a gentle angle, and suddenly the plane refuses to go down and they get long, overshooting the runway.

Now wings of a Formula 1 car work along similar lines, just upside down, so by the same argument I would actually expect that the rear wing should work better, not worse, if it has a roof above. The “air has no place to go” argument mentioned above would actually mean that the rear wing produces a markedly stronger downforce.

One logical conclusion is that any argument that explains the loss of downforce for an F1 car in a tunnel would have to fail for airplanes in order to be correct. This makes me wonder: The difference between these two cases might be very subtle, perhaps too subtle to be explainable in layman terms.

I’ve been thinking how to explore differences in configuration between an F1 car and an airplane and here is one idea I had: Perhaps it is not the flow from the rear wing, but the flow front the front wing that is at the root. It goes up, gets reflected down, hits the rear of the car and plays havoc with the flow there, so the rear wing, instead of getting nice smooth laminar flow, gets a load of dirty air and its effectiveness get compromised so much that it loses more downforce than it gains by the “ground effect” from above. Of course I might be totally wrong, I can see a few places where this story is suspect. Perhaps somebody can come up with a better one.

Speaking of tunnels, will we ever live to see somebody driving an F1 car on the roof of a tunnel? It should not be so hard, just find a very long tunnel with a circular crossection, you can enter it driving on the ground and then sort of corkscrew through it. I’m surprised Red Bull did not do it yet. If I ever win a lottery, I’m going to Marussia the first thing in the morning :-).

• andae23 said 4 months, 2 weeks ago:

@ph I’m not entirely sure, but I think it’s a matter of proportions: if you look at those ground effect aircraft, like those old Soviet airplanes that were supposed to fly across the Black Sea, the wing’s chord length is relatively large with respect to the distance between wing and ground. If you look at a rear wing and a tunnel, the chord is relatively small with respect to the distance between wing and ceiling. So I guess this reduces the effect to an extent it becomes negligible. But as I say, I’m not sure.

• pH said 4 months, 2 weeks ago:

@andae23
The ground effect is quite pronounced in all airplanes, including ordinary Cessnas whose chord is also quite small. You can even see the ground effect with model airplanes. However, you may be right that it is a question of chord/distance ratio. I do not know at what elevation the ground effect becomes significant for airplanes of various types to gain more insight into this, and I don’t have time to do the research. I tried to Google the Monaco tunnel thing, but all I found was simple statements of 20-30% loss of downforce, with only one referenced (Wiki) to a A Guide to GP Circuits by Nigel Mansell and another guy, I do not have much hope an explanation would be found there. We need somebody who actually knows the stuff here :-).
I did have a course on fluid dynamics and did my MSc thesis on PDE’s related to flow, but it was almost 30 years ago and I did not pursue it any further, so you can imagine how much I remember from that :-(. I am falling back to common sense now.

• andae23 said 4 months, 2 weeks ago:

@ph

We need somebody who actually knows the stuff here :-)

• andae23 said 4 months, 2 weeks ago: