Crucial_Xtreme wrote:Pup wrote:Dependent on the relative velocities, of course. The trick to the McLaren, if my theory is correct, is that it is doing different things at low and at high speeds. I think the shape of the outlet is turning the flow down in both cases, but at low speeds the flow is directed toward the tires (which I think is obvious from just looking at the car in plan view), and at high speeds the flow is being deflected inside of the tire, acting much like last year's exhausts. This would explain Whitmarsh's comment that the Mac this year is quicker in high speed corners than the competition - a situation they haven't enjoyed for some years now.
If the exhaust exit is placed flush in the rearward face of sidepods sweeping downwards at a fairly steep angle, then the freestream airflow could deflect the exhaust jet towards the diffuser. The degree to which the jet is deflected is determined by the ratio between the velocity of the jet and the velocity of the cross-stream flow. The smaller the ratio, the more the jet is deflected.
Hence, there is something of a trade-off necessary here. To allow the exhaust jet to be deflected down towards the diffuser requires a lower exhaust jet velocity, yet for the exhaust jet to be effective in that region, requires higher jet velocities. There may be a compromise solution available here, an optimum exhaust velocity, which permits the jet to be directed towards the outer edge of the diffuser with sufficient velocity to have an effect, but that's something which only CFD and wind-tunnel experimentation will be able to determine.
Mccabe
Of course McCabe wrote this before seeing McLaren's solution. It may be true, as is my opinion, that it would be difficult to impossible to deflect the exhaust
downward in this way enough to be very effective. As he says, you need CFD to tell you, but my intuition is that you can't. But, what I've argued with McLaren's solution is that they are using the outlet geometry to turn the exhaust down, with perhaps some help from airflow deflection, but I'm not sure it would be necessary.
On the other hand, in plan view it doesn't seem near so much of a stretch to say that they could achieve a deflection through airflow to the
inside of the wheel, since the angle isn't so great, which is why I argue that McLaren could be producing an exhaust skirt similar to, if not as effective as, last year's, but one that requires the exhaust to be deflected (by airflow) just
so to be its most effective.
If all that is true, then providing heat to the tires at low - very low? - speeds could be an ingenious part of the design, or it could just be by chance, given the exhaust angle necessary to optimize its performance at speed (meaning that it could be good or bad).
