Exhaust Blown Floor - Forward Exhaust Exit

[hardingfv32]

Ringo

1) "When air is fed under the car, it is really just to prevent stagnation and circulation from occurring."

What is meant by "circulation from occurring." What type of circulation and where exactly?

2) May I assume that there would never be a reason to inject flow under the side-pods because of their distance from the ground? There is no chance of accumulation or stagnation?

Brian

[hardingfv32]

Ringo

"This is not a tunnel floor. It is a flat floor."

I appreciate the difference in shape between a tunnel floor and flat floor. I do not understand the big difference in the flow theory.

The flow into the entrance of the flat floor is terrible when compared to a tunnel, so why isn't it a matter of the flat floor simply have less flow?

Brian

[shelly]

No you don't want air entering the sides of the floor.

There is a misconception that fans have, when they hear "feed" air under diffuser and "feed" the floor.

The teams are forcing air under the floor, you really want less air as possible.

What you don't want is the air to enter faster than it leaves the floor.

If that happens then it becomes a case of accumulation, and then stagnation.

When air is fed under the car, it is really just to prevent stagnation and circulation from occuring.

You don't put air under the car increase downforce, as ideally the opposite is better.

To get an idea of what i mean, let's say air enters the floor at 2 kg/s.

And then it leaves at 1 kg/s.

What is happening is that 1kg of air is staying in the sytem every second. It will reach a point in time where the floor effectively chokes, or certain parts of the floor is chocked and the floor behaves like a restriction.

So i never prescribed to the idea of injecting air under the floor. It never creates downforce.
You only inject when it is required, and you only inject ahead of the diffuser throat, no where else.

ringo for your post I understand that you are missing a basic point, that is that the more mass flow under the car, the better.
There is no possible occurrence of air entering at 2 kg/s and leaving at 1 kg/s: conservatio of mass in the control volume prevents this.
It is injecting air under the floor that creates downforce; I suggest you become acquainted with this before discussing further.

As a side topic, remember that water droplets are not good tracing parts for airflow: if you take water clouds patterns as flow visualisations you risk being misled and coming to wrong conclusion, as for example thinking that air does not come in from the sides of the floor.

[autogyro]

IMHO you are both right.
Renaults front lip exhaust creates a flow of hot gas along each side of the floor.
This helps to keep the mass of air flowing under the floor by working partly as a 'gas skirt'.
It can also add gas to the air under the car but if the design adds to much air,
then there will be a 'block' and stagnation, relative to diffuser limitations.
Some are saying that renaults front exhaust helps to bring the center of downforce closet to the middle of the car. I believe the RB rear blow works better
and the center of downforce is more a result of the diffuser design, floor rake etc.
IMO the floor works as two 'part' tunnels with one side 'each side' open to ambient airflow.
Renault have tried to create two full tunnels (virtual skirts) but with little success.
RB simply do everything possible to smooth and speed up air and gas flow,
by developing the rear exit of all air/gas flow.
therebye developing higher gas mass/time and more potential DF energy.

[PlatinumZealot]

Saying More OR less mass flow is not accurate.. because if your car has more space under the floor you will have more mass flow, but still a low velocity. Or you could have lightly denser air under the car.. OR you could have air joining the flow from the sides.. It is all dependent also, on which point are you taking the mass flow? Is it a certain area or an overall average? where are you taking as the control volume? these things you have to ask because The floor is not a closed system.

It is better to avoid the generalisation of mass flow and just say velocity.. I think velocity is better. Velocity is an intensive property. It does not depend on the system size. where as mass flow does.

[hardingfv32]

"ringo for your post I understand that you are missing a basic point, that is that the more mass flow under the car, the better."

This statement has to be wrong.

Why do the teams have barge boards that direct air away from the floors?

Why is the Renault exhaust simply not directed under the floor?

Your premiss is not supported by the current aero designs.

Brian

[malcolm]

"ringo for your post I understand that you are missing a basic point, that is that the more mass flow under the car, the better."

This statement has to be wrong.

Why do the teams have barge boards that direct air away from the floors?

Why is the Renault exhaust simply not directed under the floor?

Your premiss is not supported by the current aero designs.

Brian

Let me ask you a few:

Why do all the teams have raised noses?

Why do the splitters feed air toward the floor?

Why is the leading edge of the floor rounded, instead of a sharp splitter shape?

I think Shelly's premise is well-supported.

[hardingfv32]

1) "Why do all the teams have raised noses?"

Any number of reasons. Better flow for the front wing, create high pressure above the tea tray or better flow to the cooling system, etc.

If they wanted flow under the floor why is it not more easy for us to see this being done? Could there be a deflector at the leading edge of the tea tray directing more air under the floor or directing it under the side-pod floor? Something like a snowplow blade.

2) "Why do the splitters feed air toward the floor?"

I assume we are talking about the small square tunnels on the sides of the tea tray? It was suggested that this is a vortex generating system. Regardless, if this is to direct air under the floor then why doesn't this duct accumulate all the flow at the front edge of the tea tray?

3) "Why is the leading edge of the floor rounded, instead of a sharp splitter shape?"

For sure this is to generate a vortex to control the flow along the sides of the floor. A type of sealing activity.

Shelly's premise are not well-supported... in my opinion.

Brian

[PlatinumZealot]

Shelly is correct in a sense, and Ringo is correct in a sense. But one single mass flow cannot characterise the whole thing. You have to be more qualitative.

[malcolm]

1) "Why do all the teams have raised noses?"

Any number of reasons. Better flow for the front wing, create high pressure above the tea tray or better flow to the cooling system, etc.

If they wanted flow under the floor why is it not more easy for us to see this being done? Could there be a deflector at the leading edge of the tea tray directing more air under the floor or directing it under the side-pod floor? Something like a snowplow blade.

2) "Why do the splitters feed air toward the floor?"

I assume we are talking about the small square tunnels on the sides of the tea tray? It was suggested that this is a vortex generating system. Regardless, if this is to direct air under the floor then why doesn't this duct accumulate all the flow at the front edge of the tea tray?

3) "Why is the leading edge of the floor rounded, instead of a sharp splitter shape?"

For sure this is to generate a vortex to control the flow along the sides of the floor. A type of sealing activity.

Shelly's premise are not well-supported... in my opinion.

Brian

1) Better flow over the FIA mandated section so it can generate more lift? Surely you jest.

b) That's what the under-nose deflectors are for (I bet).

I highly doubt the entire front half of the car would be designed as such to optimize cooling.

2) What do you mean by "accumulate"? Air isn't piling up there. There is a slight benefit from the high pressure, but then the air gets diverted to the sides by the monocoque, and starts to direct downward. In doing so, the air is accelerated as it meets the leading edge of the sidepod, and creates better conditions for the floor to generate downforce.

3) A *rounded* leading edge to the sidepod creates a vortex? What? How would that happen?

If you and Ringo think that sealing off the floor is the ultimate method of making downforce, then why didn't teams create a sliding skirt to block off the leading edge of the floor back in the 70's, when it was allowed?

Your arguments aren't making much sense... in my opinion.

[hardingfv32]

Still confused by the subject...

I keep trying to apply Bernoulli's principle and I think I might see MY mistake on this subject.

I don't know how to say this exactly, but when you look at the illustration of the flow chamber for Bernoulli's principle the walls are all constrained or fixed. With a car's under floor flow this is not the case. The top of the floor can move. I'm am going to disregard the sides to keep it simple.

If we increase flow into the entrance but can't increase flow at the exit of the floor system (rules restricting its size), would this not mean that the pressure would increase in the front section of the system. There is not going to be any increased flow through the kink/choke point, so there will be no decrease in pressure.

Is there something to the fact that the boundaries of the flow are not fixed and react to the pressure below them? Is this the definition of an open system?

Brian

[hardingfv32]

malcolm

3)... "Why is the leading edge of the floor rounded, instead of a sharp splitter shape?"
The question was directed to the floor.

"If you and Ringo think that sealing off the floor is the ultimate method of making downforce, then why didn't teams create a sliding skirt to block off the leading edge of the floor back in the 70's, when it was allowed?"

I think the point is to let no more flow in than the restricted exit can handle.

But I could be wrong...

Brian

[shelly]

Some clarification:
-more mass flow rate gives more downforce for given ride heights
-in a detailed view, local low pressure zone affect downforce significantly
-it is wrong to say that you want as less air as possible under the floor
-air enters the floor form the sides befor the front wheels, while it tends to escape outwards after the leading
-there is no "accumulation" or "stagnation" under the floor (mass is conserved)
-barge boards do not push flow away from the floor, they increase flow under the floor
-floor leading edge is curved to create a suction peak around it, the opposite of a sealing
My opinions:
-n_smikle, I agree with you that there are more details, but the general principle s the more mass flow the better for given control volume.
-harding, I think that you imagine to much air beiong pushed and pulled by surfaces instead of flowing and curling around them

[ringo]

Shelly it is not that straight forward.

You want enough air to move as fast as possible without stalling, that is it.

Here is an example where mass flow has nothing to do with downforce:

what about zero mass flow?

Let's say i have a complete vacuum under the car, a sealed floor car (for argument sake it's sealed perfectly like a plunger and it can slide along the track while keeping the seal), no air mass at all, zero flow.

1 atmosphere will be exerted on the body of the car, pushing it to the ground.
That's 1.03 kg/cm2.

An F1 car's floor area is about 200cm x 140cm = 28000cm2

that's roughly 28,840 kg of force without any mass flow at all!

so with this example, it would seem counter intuitive to your postulation.

There are different ways to create downforce. The ultimate goal is to lower the pressure. Increasing mass flow as the goal does not directly equate to that.

Velocity is most important as smikle said. And i can tell you that, where accumulation will occur, that is what you do not want.

You cant blindly ram air under the car, thinking more is better, when in the event it can't leave as fast as it enters the car will lift.

Don't apply general principles, most of the time it will miss inform.
Each case is unique.

The key is to get air as fast as possible, leaving as quick as it enters, or quicker than it enters. The mass flow is not the goal, the goal is the velocity and hence the pressure drop.
Whatever it takes to increase the velocity.

Blowing as the R31 is, it's actually behaving like an ejector. It's sucking air by force, something the diffuser cannot do.
Sucking air then placing it back under the diffuser would be pointless.

Long story short, the air under the car is entering the splitter then diverging outwards (check the shape of the T floor and the shape of the under tray). It's not sucking in from the sides. It cant.

[ringo]

Shelly indication on this picture, where the side suction is coming from.