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Renault proved that they used to pump air through the engine for cooling purposes before the EBD concept. And according to them this is directly related to reliability.
Besides, no one here mentions KERS, because I think KERS introduces variable braking effect which is highly unwanted in view of constant car behavior when braking and therefore AFAIK its effect is compensated by some additional torque from the engine.

Dragonfly wrote: KERS, because I think KERS introduces variable braking effect ...

What is the logic for your statement.

I would think that the KERS load is fixed during application, although variable between applications. The only issue would be what happens when the batteries become full during an application.

In this regard, I wonder if the driver needs to be aware of when the batteries are full so as to adjust his braking application?

Brian

I wish to research what happens to the exhaust plume when it enters the atmosphere. What thermodynamic or aerodynamic word descriptions could be used to describe this activity? Using simple descriptions is getting me nothing.

Brian

So let us do some reverse engineering of off throttle exhaust blowing.

My first question is: Can you provide meaningful or significant blowing with the engine closed to a level of say 10% of throttle bore area?

Does the engine throttle need to be open 'well beyond' 10% for off throttle blowing to work?

Brian

hardingfv32 wrote:

Dragonfly wrote: KERS, because I think KERS introduces variable braking effect ...

What is the logic for your statement.

I would think that the KERS load is fixed during application, although variable between applications. The only issue would be what happens when the batteries become full during an application.

In this regard, I wonder if the driver needs to be away of when the batteries are full so as to adjust his braking application?

Brian

My conclusion is from reading statements from teams here and there where they sometimes mention the necessity for constant braking behavior in order to give the driver confidence in the car. Which I interpret as variable loads from KERS depending on the state of the battery. If they make it with constant load there must be another one besides the battery.
I don't say I am right, that's how I have understood it.

hardingfv32 wrote: a) After months of CDF and wind tunnel work by well budgeted and experienced personnel, there is no consensus on the location of the exhaust outlets. Completely logical conclusion: It makes no deference because the flow has a minor effect.

Brian

According to Martin Whitmarsh, McLaren believe they can recoup 25% of the EBD performance from last year. If this percentage of performance translates, to similar percentage in lap time, then we are looking at a gain of a quarter of a second, maybe more. If that is the case, I don't believe that this is a 'minor effect'.

hardingfv32 wrote: Does the engine throttle need to be open 'well beyond' 10% for off throttle blowing to work?

Brian

I don't believe that is the case, but of course it would be less effective. In any event doesn't the following articles prevent such a strategy:

5.6.6 Except when anti‐stall or idle speed control are active, ignition base offsets may only be applied above 80% throttle and 15,000rpm and for the sole purpose of reducing cylinder pressure for reliability.

Blaze1 wrote:

hardingfv32 wrote: a) After months of CDF and wind tunnel work by well budgeted and experienced personnel, there is no consensus on the location of the exhaust outlets. Completely logical conclusion: It makes no deference because the flow has a minor effect.

Brian

According to Martin Whitmarsh, McLaren believe they can recoup 25% of the EBD performance from last year. If this percentage of performance translates, to similar percentage in lap time, then we are looking at a gain of a quarter of a second, maybe more. If that is the case, I don't believe that this is a 'minor effect'.

True, and the other obvious rebuttal is that before Newey started the whole exhaust blowing trend, there was also no consensus as to where to locate the exhausts; and yet as we saw, there was a great deal of performance to be gained. We can't just assume the teams' omniscience.

hardingfv32 wrote:I wish to research what happens to the exhaust plume when it enters the atmosphere. What thermodynamic or aerodynamic word descriptions could be used to describe this activity? Using simple descriptions is getting me nothing.

Brian

When an exhaust jet exits into a cross-stream, the jet almost behaves like a deformable solid.


Search for this paper--> Aerodynamic effectiveness of the flow of exhaust gases in a generic formula one car configuration

by F.L.Parra and K.Kontis in 2006

Dependent on the relative velocities, of course. The trick to the McLaren, if my theory is correct, is that it is doing different things at low and at high speeds. I think the shape of the outlet is turning the flow down in both cases, but at low speeds the flow is directed toward the tires (which I think is obvious from just looking at the car in plan view), and at high speeds the flow is being deflected inside of the tire, acting much like last year's exhausts. This would explain Whitmarsh's comment that the Mac this year is quicker in high speed corners than the competition - a situation they haven't enjoyed for some years now.

Pup wrote:Dependent on the relative velocities, of course. The trick to the McLaren, if my theory is correct, is that it is doing different things at low and at high speeds. I think the shape of the outlet is turning the flow down in both cases, but at low speeds the flow is directed toward the tires (which I think is obvious from just looking at the car in plan view), and at high speeds the flow is being deflected inside of the tire, acting much like last year's exhausts. This would explain Whitmarsh's comment that the Mac this year is quicker in high speed corners than the competition - a situation they haven't enjoyed for some years now.

If the exhaust exit is placed flush in the rearward face of sidepods sweeping downwards at a fairly steep angle, then the freestream airflow could deflect the exhaust jet towards the diffuser. The degree to which the jet is deflected is determined by the ratio between the velocity of the jet and the velocity of the cross-stream flow. The smaller the ratio, the more the jet is deflected.

Hence, there is something of a trade-off necessary here. To allow the exhaust jet to be deflected down towards the diffuser requires a lower exhaust jet velocity, yet for the exhaust jet to be effective in that region, requires higher jet velocities. There may be a compromise solution available here, an optimum exhaust velocity, which permits the jet to be directed towards the outer edge of the diffuser with sufficient velocity to have an effect, but that's something which only CFD and wind-tunnel experimentation will be able to determine.

Mccabe

Blaze1 wrote:According to Martin Whitmarsh, McLaren believe they can recoup 25% of the EBD performance from last year.

The context of this statement needs to be expanded. Are they talking about the recouping general rear car down-force levels or the performance of the diffuser?

Brian

Crucial_Xtreme wrote:Search for this paper-->

I have it, but forgot. I often change the name to something I THINK we help me find it again. Does not always work.

In the chart above, the left column is labeled (not shown) 'Turbulent kinetic energy'. What is a simple explanation for what that means? The charts name is "Velocity contours around
the exhaust area".

Why is the value some distance off the surface of the wing/body similar to the value leaving the exhaust pipe.

PM me if you want a copy.

Brian

Crucial_Xtreme wrote:

Pup wrote:Dependent on the relative velocities, of course. The trick to the McLaren, if my theory is correct, is that it is doing different things at low and at high speeds. I think the shape of the outlet is turning the flow down in both cases, but at low speeds the flow is directed toward the tires (which I think is obvious from just looking at the car in plan view), and at high speeds the flow is being deflected inside of the tire, acting much like last year's exhausts. This would explain Whitmarsh's comment that the Mac this year is quicker in high speed corners than the competition - a situation they haven't enjoyed for some years now.

If the exhaust exit is placed flush in the rearward face of sidepods sweeping downwards at a fairly steep angle, then the freestream airflow could deflect the exhaust jet towards the diffuser. The degree to which the jet is deflected is determined by the ratio between the velocity of the jet and the velocity of the cross-stream flow. The smaller the ratio, the more the jet is deflected.

Hence, there is something of a trade-off necessary here. To allow the exhaust jet to be deflected down towards the diffuser requires a lower exhaust jet velocity, yet for the exhaust jet to be effective in that region, requires higher jet velocities. There may be a compromise solution available here, an optimum exhaust velocity, which permits the jet to be directed towards the outer edge of the diffuser with sufficient velocity to have an effect, but that's something which only CFD and wind-tunnel experimentation will be able to determine.

Mccabe

Of course McCabe wrote this before seeing McLaren's solution. It may be true, as is my opinion, that it would be difficult to impossible to deflect the exhaust downward in this way enough to be very effective. As he says, you need CFD to tell you, but my intuition is that you can't. But, what I've argued with McLaren's solution is that they are using the outlet geometry to turn the exhaust down, with perhaps some help from airflow deflection, but I'm not sure it would be necessary.

On the other hand, in plan view it doesn't seem near so much of a stretch to say that they could achieve a deflection through airflow to the inside of the wheel, since the angle isn't so great, which is why I argue that McLaren could be producing an exhaust skirt similar to, if not as effective as, last year's, but one that requires the exhaust to be deflected (by airflow) just so to be its most effective.

If all that is true, then providing heat to the tires at low - very low? - speeds could be an ingenious part of the design, or it could just be by chance, given the exhaust angle necessary to optimize its performance at speed (meaning that it could be good or bad).

Brian, I'd be interested in a copy please...Searched and searched but they all lead in circles