It doesn't move to atmospheric instantly, if it's presented with an obstruction the pressure will increase. Keep in mind the mass flow of the air and Newton's third law. The pressure rise against your hand is equal and oppossite to the pressure of the gas. The exhuast drops to atmospheric with some time, but would only be instant with a propper diffuser on the pipe.Raptor22 wrote:from the renault r31 threadn smikle wrote:
It has energy in the form of speed and temperature. When you impede it's motion or diffuser it the pressure will rise. Naturally it is going to drop to atmospheric after some time outside the pipe, but for example if ones uses their hand to block the pipe and you will see the pressure can get high.
There was a pdf on a CFD analysis of the blown diffuser floating around the internet. the pressure behind the exhaust was higher. I do not know how much higher though, but it can be significant if the exhaust is impeded.
Sorry but thats not correct at all. What you are feeling is the pressure rise against your hand not the exhaust pressure. When thehot gas leaves the boundary of the pipe it moves to atmospheric pressure instantaneously. Your hand is feeling pressure due to the velocity of the gas and is not a pressure that will be felt by the underside of the car.
The airflowingunder the car will be accelerated by the faster moving exhaust gas. It is this acceleration of the normal airflow due to the added kinetic energy and thermal energy loss to expansion that accelerates the air flow under the car. That drops the pressure under the car increasing downforce under the stepped bottom.
it is this alone that is doing the magic, nothing else.
Using a exhaust exit in or near the diffusor is slightlyless effective because you impart less kinetic energy to the freestream due to loss of knetic energy due to skin friction. Both concepts allow for accelerating the air flow under the car.
Lotus Renaults solution may have a slightly higher expansion ration resulting a few kilo more downforce but that expansion is now taking place over a much bigger surface area which could negate the benefit.
Yea this is true but that little flick up next to the vertical wing nest to the entrance of the side pod creates a vortex, thus forming the "exhaust side skirt"nacho wrote:To me it looks like that the pipe will blow 100% under the floor.
The exhaust doesn't block the air from entering below sidepods since it is leveled up with the floor and most of the air passes below exhaust pipe.BreezyRacer wrote:I agree pretty much with Ringo's assessment except that imagine almost all the exhaust flow is under the car .. the exhaust flow acts as a barrier to KEEP FORWARD AIR FROM GOING UNDER THE CAR .. thus more low pressure area under the car, and low pressure created as far forward in the chassis as is possible.
The exhaust flow will exit nearly perpendicular to the car and interrupt the forward air off the the sides of the under tray.
You want LESS airflow under the car to create as much low pressure as is possible .. at least until you get so little airflow that there is no flow
Or maybe they have at least allowed space in their sidepods to route the pipework there in the future should they feel the need! I notice that the area in the corner of the floor on the Lotus (where the bargeboard attaches) is similarly "lumpy" perhaps this is indeed hiding something?andrew wrote:Looking at the pictures of the Lotus on the Lotus thread, they have these small fences in front of the rear wheels also. Certainly a renault idea and ties in Forty Two's theory on the first page of this thread.
Can't see the exhaust outlets on the Lotus due to the barge boards being in the way but I'll wager they have the same exhaust configuration.
Interesting, but I guess that it doesn't mean they haven't been working on this for a while now. Putting the fence there last year might well have taught them important lessons about the flow in general, even without the exhaust blowing there.richard_leeds wrote:That fence in front of the rear wheel was on the R30, so not a new feature for the forward exhaust
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