OV9

NotoriousREV wrote: Tue Aug 07, 2018 12:01 pmNope.

I wasn't even the first to post that it's a high pressure area - Harry did earlier.

As if the flow/pressure analysis image I posted wasn't enough, I did add a link as well. But google it yourself.

The link is full of amateur pseudo-science that sounds impressive and logical but actually doesn't stand up to any analysis. Your first clue is when he admits he's not an expert and then proceeds to claim that air rushing under the car pulls air from the engine by via the Venturi effect (it doesn't, it is Entrainment as described the the Bernoulli principle, of which the Venturi effect is a small subset).

Whilst it is true that a high pressure area forms where air gets dammed by the windscreen, to comes down to the design as to where that high pressure area occurs. On an older vehicle, like Ste's Viva, that high pressure area will be at the base of the screen. On a more modern vehicle where the wipers live in a little trough nestled behind the trailing edge of the bonnet, the high pressure area forms higher up (the entire idea being that airflow is directed above the wipers for a cleaner flow and less wind noise). Thus this trough area becomes a low pressure area (compared to the areas around it), plus you have the airflow over the top of the trough providing further entrainment of air (in just the same way as the chap in your link says the air is drawn out of the undertray). Adding stand-offs to Ste's Viva would yield some of this effect, but less successfully.

So air is pushed into the front of the engine bay at pressure, pumped full of heat energy via the heat exchangers and engine itself, and is then drawn out by air entrainment via any route it can take into cooler, faster flowing air.

The diagram you posted shows a NASCAR that isn't designed to have wipers and therefore has a completely smooth transition from the trailing edge of the bonnet to the base of the screen, so yes, for that car, the high pressure area would live there.

To summarise, if you painted a Pikes peak car mole brown, put it on tank tracks and jacked up the bonnet hinges it could qualify on pole in the Belgian Grand Prix whilst being the logical choice to replace the VW Scirocco.

Rev, that's complete and utter bollocks.

I've seen really in-depth CFD studies about this, will dig them out.

Rich B wrote: Tue Aug 07, 2018 1:04 pm To summarise, if you painted a Pikes peak car mole brown, put it on tank tracks and jacked up the bonnet hinges it could qualify on pole in the Belgian Grand Prix whilst being the logical choice to replace the VW Scirocco.

FFS - just how dumb are you?

Only if you buy it on finance from a dealer!! And then have to pay a fortune to hand it back to buy a car that doesn't work because #YOLO and heir apparent.

JLv3.0 wrote: Tue Aug 07, 2018 1:10 pm

Rich B wrote: Tue Aug 07, 2018 1:04 pm To summarise, if you painted a Pikes peak car mole brown, put it on tank tracks and jacked up the bonnet hinges it could qualify on pole in the Belgian Grand Prix whilst being the logical choice to replace the VW Scirocco.

FFS - just how dumb are you?

Only if you buy it on finance from a dealer!! And then have to pay a fortune to hand it back to buy a car that doesn't work because #YOLO and heir apparent.

Of course! I don’t know how I missed that!

ste wrote: Tue Aug 07, 2018 1:09 pm Rev, that's complete and utter bollocks.

I've seen really in-depth CFD studies about this, will dig them out.

Go for it.

Answer this: are the wipers of a modern vehicle that are hidden in this trough in or out of the airflow?

This is an image from GM:



This is another one (with a flush bonnet and no trough) that also shows that the high pressure area is higher up the screen than the trailing edge of the bonnet:

Is this not completely dependant on the car and speed it runs at ?

Surely what happens with the air at 100mph is different to 150 ?

Also, don't some cars have issues getting air out of the engine bay?

I fitted a 300mm X 300mm louvred panel in my 500e under tray and it runs noticeably cooler on B-Roads because of it. It also cools down after being in traffic much cooler which says to me it needed air sucking out from underneath.

I'm sure I remember seeing a test on this very thing on a forum somewhere, someone with Googlefu may be able to find it.

Dave!

I’ve never seen a race car or supercar with raised bonnet hinges which is about all the evidence that I need to know that they probably don’t work very well.

Sounds like people think it makes them into professional drifters who are trying to cool their cars down whilst waiting their turn to go out and do skids.

That’s obviously why this fwd Corsa driver has done it.

Rich B wrote: Tue Aug 07, 2018 1:04 pm To summarise, if you painted a Pikes peak car mole brown, put it on tank tracks and jacked up the bonnet hinges it could qualify on pole in the Belgian Grand Prix whilst being the logical choice to replace the VW Scirocco.

Logical but too late, they replaced it with the T-Roc


Wrt to sitting under the bonnet line or the like, you used to be able to get a spoiler for the rear of the bonnet for mk3 Golfs for that effect.

V8Granite wrote: Tue Aug 07, 2018 3:38 pm
I fitted a 300mm X 300mm louvred panel in my 500e under tray... (snip)

Was it brown or black?

NotoriousREV wrote: Tue Aug 07, 2018 1:49 pm This is an image from GM:

This image sums up how I would anticipate the airflow to behave in this area. Which is why I can see Rev's point.

However I don't believe it's a sensible or effective way of cooling an engine.

Could we have GGs take on this before we ahead into round 2?

Can’t we just get Beany to vape one of his contraptions and blow over a few cars? It will be just like a wind tunnel and we can see the cold hard reality.

I've badly skim read this thread and concluded that Revs has evidence that windscreen wipers cool your engine.

Is this a correct assumption?

Marv wrote: Tue Aug 07, 2018 7:43 pm I've badly skim read this thread and concluded that Revs has evidence that windscreen wipers cool your engine.

Is this a correct assumption?

Yep, they waft the air out with each sweep.

NotoriousREV wrote: Tue Aug 07, 2018 7:58 pm

Marv wrote: Tue Aug 07, 2018 7:43 pm I've badly skim read this thread and concluded that Revs has evidence that windscreen wipers cool your engine.

Is this a correct assumption?

Yep, they waft the air out with each sweep.

It's a kind of magic

Well I must say, I’m very disappointed in the progress of this thread.