Exhaust Blown Floor - Forward Exhaust Exit

[malcolm]

I find it hard to believe that the exhaust of an F1 car is exiting at 792 km/h.

Maybe this exhaust does: http://www.youtube.com/watch?v=R1b7RDsQCek

Even that exhaust stream leans back quite a bit somewhere around the 200 mph mark.

[shelly]

Imagine 220m/s of hot gas shooting out 90 degrees. Will we expect that to bend and go under?

yes

[Giblet]

The gas is only going that fast at the exhaust opening. It slows, cools, and disperses as soon as it leaves the pipe

[malcolm]

So everyone agrees that the exhaust is leaving the pipe at 792 km/h? Roughly 2/3 the speed of sound?

Even if it slows by 50% after 20 cm, it's still going almost 400 km/h.

If that was the case, I'd be tempted to use it for thrust!

[malcolm]

1) This is what I have an issue with. Look at the flow lines around that little text box. They are going straight toward the rear tire, and only seem to bend in once they feel the effect of the tire. Every other plot seems to show a gradual curve where the lateral, outward momentum provided by the splitter is gradually overcome by the suction of the diffuser kink line.



It just seems like something is wrong with the diffuser if it isn't at least somewhat affecting the flow-field up-stream.



2) The exhaust exit isn't 90 degrees... it's closer to 70 or so:



Big difference.



3) You created this image here:



It only shows the top... yet the exhaust tends to stick to the sidepod. How is it so inconceivable that the exhaust going underneath follows a similar route to the rear diffuser? Beyond that, if you isolated the exhaust in this image, why is it not shooting out wide in the image like you say it is?

[malcolm]

One thing I would like to figure out is what the temperature of the exhaust is as it leaves the end of the pipe. It would have transferred a lot of heat out through the headers, the long pipe, etc. Is 1000 C really realistic? High? Low?

I just did a quick calc...

At 1000 C out (25 C in), an exit of 80 cm^2 (roughly 10 cm diameter pipe), I get 192 m/s. At 800 C out, I get 162 m/s. At 1200 C, I get 222 m/s.

Also, if I increase the diameter to 11 cm, we get 95 cm^2, which results in 161 m/s at 1000 C exhaust temp (or 136 m/s @ 800 C).

Pretty big variances!

So, I think it's fair to say we need to figure out these parameters before we boldly say that it is certainly 220 m/s, or 136 m/s.

[PlatinumZealot]

The BAR honda diffuser is not applicable because the diffuser throat is before the rear wheel centre line. From 2009 and up the diffuser throat has to be behind the rear wheel centre line.

[malcolm]

Fair... but would the diffuser lose that much performance? What about with the tighter rear ends, cleaner flow to the beam wings, and slotted gurneys over the diffuser? Must have clawed back some of that, and given the relative lap times compared to pre-2009, I would guess that the diffusers are roughly equivalent.

So while they are slightly different in design, wouldn't they have largely similar effects on the floor upstream?

[ringo]

Malcom the last image it with a very low speed of exhuast. Look on the chart.
Someone asked about that. And i showed it. That was when we didn't specfiy a speed and were just trying to see what may be happening.
The pipe was split half way between top and bottom of the floor.

In fact both iterations there are prototypes.

the latest ones i have shown are more accurate.

[youtube]http://www.youtube.com/watch?v=8CtLB7g5s9s[/youtube]

[ringo]

Imagine 220m/s of hot gas shooting out 90 degrees. Will we expect that to bend and go under?

yes

Why, what is you conviction?

Just yes just like that...

Who's pulling the strings?

There is someone in the background supplying you with information.

whoever it is, show yourself!! and bring your evidence.


Can you find the recording of the last race with the renault passing through the dust please? Let's discuss that.

[malcolm]

Thanks Ringo. That video seems to match up with what I had in my head. I still think some benefit is had by having some of that exhaust go under the diffuser, and it could easily do so if the Renault is even slightly different from the model physically, but that small difference having a large effect on the airflow and exhaust-flow.




Another idea, alluded to by Ringo's earlier CFD (and perhaps alluded by Ringo himself; apologies if I missed it):

The divergence of the exhaust from the centre-line of the car may create the effect of a diffuser under the front half of the floor.

Since the exhausts shoot outward, it creates a diffuser-like effect on the floor under the side-pods, which in turn encourages a bigger suction peak under the splitter and between the exhaust exits on raised part of the floor. This, of course, would hurt the diffuser performance somewhat, but if Renault wanted more front aero grip, it would obviously benefit them.

Now, it would seem to me to hinge on the effectiveness of the exhausts at pushing the air outward more, which is something I don't know much about.

Just thinkin' out loud.

[ringo]

That's all i was saying.

It doesn't hurt the diffuser either.
The diffuser performs better than an non blown flow, but not as good as rear blown floor.

[malcolm]

...but I still think more exhaust ends up getting pulled in by the diffuser than your model shows.

I think I'm done here for now.

[ringo]

Hellohooooh!!

On average, in the corners, the speed of the exhaust gasses is around 6 times the speed of the car. If this high speed gas can be directed at the underside of the floor, then as far as the part of the floor that is in contact with the exhaust is concerned, it will produce downforce just as if it was going 6 times as fast. The extra downforce that is produced is substantial and can improve the laptime of the car by around 1sec/lap. “

discuss.

[strad]

On top of that, someone needs to get that clip of the renault entering the concrete dust cloud.....
Can you find the recording of the last race with the renault passing through the dust please? Let's discuss that.

WHat is it you're looking for? I'll try to cap it..Spain?
I thought exhaust flow was in the 240-260 ft/sec.