Exhaust Blown Floor - Forward Exhaust Exit

[malcolm]

Actually, it's not similar at all.

If you look at the Honda plot, you can even see that lone streamline that almost makes it to the edge of the floor, and then curves back in, without the aid of the tire. All of the streamlines, with the exception of the ones that crash into the tire, follow a nice curve that looks like the side of an ellipse... whereas yours look like straight lines that suddenly curve when they approach the tire.

Something's different with your CFD. Not sure if it is detail in the splitter, or if the exhaust is what is causing this effect...

Did you try any runs with no exhaust shooting out? What did those plots look like? I'd like to see how they match up to the Honda and USF1 ones.

[ringo]

It's from the tyre.

There is a high pressure field in front of the tyre that you can't see. It's a 3 dimmensional volume of high pressure.

To say it's not similar at all, is disingenous. Anyone can look and see the simialrity.

Have you seen the renault kick up concrete dust today?

did it go under the car?

The thing that is different in my cfd is the regs. This car is a 2009 car, so floor, barge board and splitter are all different from the honda.

They wont match up perfectly, as the car is not the same, and neither is the speed, you don't know that from teh USFq or the Honda, but there is still a striking similarity given all the variables.

conclusion: Flow only goes under the floor after obstruction from the tyres.
None goes under the side on it's own by diffuser "suction".

refer back to the MS paint; agree?

From this it makes no sense half the exhuast deflects outside the tyre, and a low energy turbulent stream trickles into the inside of the wheel after deflection.

[hardingfv32]

Why was Renault the only car to kick up a large dust cloud during the opening lap of the race in one of the turns? The cars in front and in back did not produce the same cloud.

Brian

[PlatinumZealot]

I think that was the damning evidence. The car blew the chalk dust sideways through one of the turns.

[malcolm]

About the differences of the models, fair enough. The Honda plot still shows, however, that a streamline from the splitter can diverge all the way to the edge of the floor, and then still get sucked back to the diffuser. Regardless of what makes the air go out to the edge of the floor, the diffusers on each car would be similar enough that it would have roughly the same amount of "pull" on an "air particle" in the same location, going roughly the same direction.

Anyone capture that dust cloud in photos or a video? I would like to see a reply. I saw it live, but didn't notice where the cloud went.

Also, since the tires were kicking up much of the dust, obviously quite a lot of that cloud will fill the turbulent region behind the front tire, and obscure the view of the floor. That's not really a smoking gun for anyone's theories.

To clarify, my argument is that some of the exhaust will end up in the diffuser, some of the exhaust helps the suction peak at the leading edge of the floor (which I don't think anyone on here disputes...), and having that hot jet of exhaust will also heat the air that goes around/through it and under the floor.

Also, another reason why they may not have extended the exhaust to face backwards is that such an exit would create a very localized hot area under the floor, whereas shooting a jet of exhaust laterally would "spread" the heat out across the entire width of the floor, maximizing the effect and minimizing the need for super-heat-resistant materials in one section of the floor. By having that lateral exit, the advantage wouldn't just be the hot jet itself, but the hot jet plus all the air that it has mixed with. (Just thought of that now)

Now, I'm not an expert on jets and mixing theory... and I don't have access to CFD. Is there a relatively easy way to run CFD and check how a hot jet would affect temperatures of the rest of the air going under the car?

[hardingfv32]

Your thought about the heat issue is good.

The video shoot was at some distance so you are not going to see any additional info. We cannot even be sure if the Renault actually did not go off line, but the cars seemed to be tracking normally.

Brian

[malcolm]

Basically, why put extra pipe there when the cross-flowing air stream will do it for you?

(and disperse it more to heat more air... and reduce localized heating of components/bodywork...)

[shelly]

@ringo:"accumulation" does not occur. As afr as your cfd image, it seems that the floor is not working in it. Do you have an image with pathlines and pressure ditribution on the floor?
In a downforce producing floor, there are two suction peaks and the stremtube is boud to grow larger between them. If you do not see that pattern in you cfd, it could be that the fooor is stalled

[ringo]

Shelly i am going to post the same things again until you all look at them without focusing on playing devil's advocate.

Come on shelly come on!!


The floor works. It was always working.





These above are with and without FEE. FEE is the top one, notice the size of the suction peak at the front comared to without.

Velocity plots are the second image. FEE being the top image. Look on the floor edges. Look how much slower the speeds are at the floor edge without FEE.

The gases need to run outside the floor to keep up the speeds to increase the effective floor area.


Malcolm temeprature is not an issue with the pipes having good exposure to the airflow, unlike the rear blown designs that run close to the body. The airstream absorbs a lot of it


This is the gas temperature, distance taken from the rear wheel center line if i remember. 2.5m is at the pipe exit.

[ringo]

Your thought about the heat issue is good.

The video shoot was at some distance so you are not going to see any additional info. We cannot even be sure if the Renault actually did not go off line, but the cars seemed to be tracking normally.

Brian

What is for certain is that it blew the dust far. It wasn't the wheels either. Other cars passed over in the same way without the same effect.

Can some one post the clip please. I know someone must have access.

[ringo]

@ringo:"accumulation" does not occur. As afr as your cfd image, it seems that the floor is not working in it. Do you have an image with pathlines and pressure ditribution on the floor?
In a downforce producing floor, there are two suction peaks and the stremtube is boud to grow larger between them. If you do not see that pattern in you cfd, it could be that the fooor is stalled

here's some more:



i'm going to run a quick sim now and show the line with the surface plot.

edit: shelly rake is also a very big factor with the flow under the floor.

edit:
took a while but here is a close up. No exhuast blowing this time, just normal flow.


keep an eye on the side flow. Car has a little rake here to make things easier to go under.

See where the tyre comes in?

No imagine the exhaust shooting wide, and be objective and try to imagine if it will go under the diffuser by suction.
From what i can see, nothing goes under unless it loses energy in the tyre and has no choice but to deflect either left or right. The sides of the floor are perflectly fine, thanks to the sidepods above the floor having a low pressure along the side of them.

[shelly]

It is strange to see pressure plots instead of cp. Why do not use cp? Is is easier to understand. The behaviour of the floor from your pictures seems unusual, like the floor is stalled and /or the solution is not converged. Maybe it is just an impression due to the representation in presssure instead of cp.

If the floor is not working, a direct consequence is that you do not have suction and you do not see streamline deflection. From this pictures pressure on the side rea part of the floor seems too high for it to be working.
The colorscales you chose are narrow, so it is not possible to appreciate that.
To make some considerations a wider color scale is necessary, or better a cp map on the floor

[ringo]

Coefficent of pressure has to be calculated.
I can do that, but i do it manually within a plane. I only do that if i am interested in the centre of pressure relative to the COG.

COP is just a dimensionless representation. It doesn't change the fact that the suction peaks are where the lowest pressure is.

Take note of the scale as well look on the pressures. 101325 is atmospheric in this test. Car is moving at 90m/s.

I use pressure plots and velocity plots as they are more informative.

COP is for solid surfaces as well. I've never seen it used in open volumes.

[ringo]

It is strange to see pressure plots instead of cp. Why do not use cp? Is is easier to understand. The behaviour of the floor from your pictures seems unusual, like the floor is stalled and /or the solution is not converged. Maybe it is just an impression due to the representation in presssure instead of cp.

If the floor is not working, a direct consequence is that you do not have suction and you do not see streamline deflection. From this pictures pressure on the side rea part of the floor seems too high for it to be working.
The colorscales you chose are narrow, so it is not possible to appreciate that.
To make some considerations a wider color scale is necessary, or better a cp map on the floor

What standard are you using to say that my floor is "stalled"?

Look on the one with the flow lines. Do the lines look like they have no energy?

I'm interested in where you are getting your information from.
By what authority is your information correct?

I should be the one inquiring as to what information you have.

I know what i am doing. Nothing is wrong with the car. Something is wrong with your source of information.

The colour scales i chose are purposely narrow. It gives the most detail. If it's too wide you can't see the small changes in the flow.
I am more interested in the lower pressures in this plot.

Enough of the recommendations, show me your source of CFD authority.

Bring you data to the table. Your high horse is standing on shaky polio legs.

[shelly]

ringo, why do you get so upset?
What I say is very simple: if your coroscale is such as all the difuser is painted in the same shade of blue, it is not possible to see the pressure gradient along the difuser and to isolate the suction peak on the kink line. Also it is not possible to compare front suction peak intensity with the rear one.
Your flow lines do not seem to be consistent with the behaviour of a floor with a rear suctio peak as intense as the front, hence the oubt that maybe it is stalled.

Why do you call for authority? It seems the last resource when you can not discuss and motivate your point. Do you want a technical discussion to turn into a spaceball fight "my authority is bigger than yours"?