Sidepod design and the Meredith effect

[Tommy Cookers]

can't this 'not the Meredith effect' effect reasonably be called entrainment ?

[bhall II]

[...]

I'm talking about the air that sits directly behind the the raised rear body work. To my mind there is no way that air can be clean, I personally think of it like a car travelling down a motor way and someone opens the window - you have air swirling around as it rushes to get into the car.

[...]

Yes, and I think the idea in this case was to extend the sidepod vents as far aft as possible in an attempt to coax air flow from the diffuser to fill the "void" left by the wake, thereby increasing the diffuser's efficiency. It's the same idea behind the mushroom suspension shrouds. I think the idea is probably sound, but McLaren may have missed the boat in terms of execution. To wit...



Notice how Mercedes, Red Bull, and Ferrari have all extended the vents low and straight. That they're low sorta takes the place of having a mushroom shroud on the lower suspension arm. That they're straight means they mitigate the tendency of the sidepods to produce lift, because any time you "bend" air over a surface, you create lift one way or other other. (The idea for the low placement is mine, but the one for the straight sidepods is flyboy's, and I agree with it.)

[flyboy2160]

The velocity of the air exiting these new aftmost chassis vents relative to free stream depends on the entire overall flow design of the sidepod. You could deliberately design the system so that the air existing is slower than, equal to, or [edit] perhaps faster than free stream (which would be sort of a Meredith Effect.) This choice also would affect radiator performance and design - and vice versa.

If it's slower, then The Deuce's hypothesis about creating a suction area to help the diffuser is correct. It's still not clear to me that the diffuser must work better with an additional suction area above it as opposed to getting the cleanest, highest velocity air just above the top diffuser lip.

I've hypothesized from the start that the new extended vents might also be to reduce the camber, and thus the lift, of the sidepods.

[bhall II]

This might be the first instance in which your idea about employing the Meredith effect has really crystallized in my mind, Steve. (Like everything other than the W05, I can be slow.)

Yeah, I agree with you now. For others: the Meredith effect is using a vehicle's cooling system to somewhat compress and heat cooling flow via the radiators and flow paths to provide genuine thrust when that flow is vented. Done right, Meredith virtually eliminated drag associated with cooling on the P-51, but it's somewhat sensitive to temperature (generally, the hotter the better).


Look at me actin' like I actually know what the hell I'm talkin' about.

So, maybe the idea is to use Meredith to neutralize sidepod drag, which I believe has been done in F1 before, and I bet McLaren's high placement of the vents is the mistake if their solution doesn't work as well as Mercedes, Red Bull, Ferrari, etc.

I guess they stacked the mushroom suspension shrouds to increase diffuser efficiency, and then used high-placed vents to help make that work. If it doesn't work so well, that would mean the ideal solution is probably to use the relatively high-velocity air lower in order to vent directly over the diffuser instead, sorta like McLaren's first iteration of the EBD in 2010. Plus, you can then reduce the overall camber of the sidepods because of the low placement of the vents.


MP4-25; note how the floor is bent up around the wheel seemingly to guide the exhaust plume over the diffuser rather than to "seal" it, as would be the case for all later EBDs.

[flyboy2160]

Getting that Meredith deal to work at more than a single "point" design takes some serious trickeration and strategery. At work I was once involved in putting an intake/radiator/exit system into an aircraft sensor pod that had to operate over a relatively wide airspeed range (wider than the F1 speed range.) We concluded that we needed variable geometry on both the intake and the exit. If I recall correctly from the old Mustang literature, the air temperature delta also has a role.

If I was forced to bet, I'd wager on the exit air being slower than free stream in order to get the greatest pressure drop across the radiators. Again, if memory serves me correctly, to get the Meredith increased exit velocity, you need a plenum pressure downstream from the radiator that's higher than otherwise. This decreases the pressure drop across the radiator, affecting its performance. You can design for it, but you have to have the whole system scheme in mind.

[mclaren_mircea]

The velocity of the air exiting these new aftmost chassis vents relative to free stream depends on the entire overall flow design of the sidepod. You could deliberately design the system so that the air existing is slower than, equal to, or faster than free stream (which would be sort of a Meredith Effect.) This choice also would affect radiator performance and design - and vice versa.

If it's slower, then The Duce's hypothesis about creating a suction area to help the diffuser is correct. It's still not clear to me that the diffuser must work better with an additional suction area above it as opposed to getting the cleanest, highest velocity air just above the top diffuser lip.

I've hypothesized from the start that the new extended vents might also be to reduce the camber, and thus the lift, of the sidepods.

Great tech analysis. I really enjoyed it =D>

[wesley123]

There was already a topic about the Meredith effect; http://www.f1technical.net/forum/viewto ... =6&t=15179

Anyways, if I remember correctly, the Meredith effect works with speed, it becomes many times more effective at plane speeds than at the relatively slow speeds F1 cars travel at. In short; The Meredith effect would have fairly little effect on F1 cars.

Also, the Meredith effect makes use of changes in pressure. Seeing how many times we have seen bodywork torn apart, I don't think F1's bodywork would be capable of dealing with it.

The internal bodywork of F1 cars is designed to make the flow through it as smooth as possible with the least obstruction possible, this to reduce drag.

[bhall II]

[...]

Also, the Meredith effect makes use of changes in pressure. Seeing how many times we have seen bodywork torn apart, I don't think F1's bodywork would be capable of dealing with it.

The internal bodywork of F1 cars is designed to make the flow through it as smooth as possible with the least obstruction possible, this to reduce drag.

I disagree with the assertion that it can't work. The McLaren appears to rely on pressure differential to move air through the radiator, otherwise it would just flow right by.



Think of it this way: you don't need it to work in a wide performance window, because acceleration is about power-to-weight until the car reaches 100mph; that's when drag seriously becomes a factor. So, you've already basically cut the window in half in the context of a car's inherent capability.

You're also not looking for a massive gain. If that drag reductions brings 0.1 or 0.2 seconds, it's a success.

And flyboy, how is it that you put this idea in my head, and now I'm the one defending it, in part, from you? Is it some sort of Jedi mind trick?

[wesley123]

[...]

Also, the Meredith effect makes use of changes in pressure. Seeing how many times we have seen bodywork torn apart, I don't think F1's bodywork would be capable of dealing with it.

The internal bodywork of F1 cars is designed to make the flow through it as smooth as possible with the least obstruction possible, this to reduce drag.

I disagree with the assertion that it can't work. The McLaren appears to rely on pressure differential to move air through the radiator, otherwise it would just flow right by.

Not saying it cannot work, just saying it's effect isn't large enough to have an significant effect on drag reduction

Think of it this way: you don't need it to work in a wide performance window, because acceleration is about power-to-weight until the car reaches 100mph; that's when drag seriously becomes a factor. So, you've already basically cut the window in half in the context of a car's inherent capability.

A quote from the topic I posted earlier;

A big difference being, of course, that the P-51's radiator was a variable nozzle device. Remember that an aircraft has a much, much, lower drag than an F1 car so the radiator's drag would be a huge percentage of the total. It's therefore worth the effort of trying to reduce it. On an F1 car, the radiator's drag will be a pretty small percentage of the overall drag. Finding reductions elsewhere (such as the rear wing endplate slots, or the outflow front wing endplates) will give bigger drag reductions whilst also improving downforce.

Even if the effect would be the same, then still it's overall effect wouldn't match. Like Just_a_fan says; On the Mustang, the cooling system contributed to a much larger percentage of the drag created than F1 cars. F1 cars have those big, cambered wings and open wheels contributing to a much larger portion of the drag created than the cooling system.

So while on the Mustang it had a large effect on the overall drag, on an F1 car it would not.

[bhall II]

You sorta glossed over some of my important points. So, I'll expand upon those (probably too much) in order to make them a bit easier to see.

If one of the requirements for Meredith is a pressure differential to move air through the radiators, allow me to present Exhibit A.



Notice how each radiator is angled and sealed on the intake side. If teams didn't take any measures to control the pressure differential between the front of the radiator and the back of the radiator, cooling flow would either fill the sidepod inlet and spill over the sides if air flow couldn't pass through quickly enough, or it would pass through too quickly and only through the rear-most portion of the radiators. Neither seems very efficient to me, yanno?

So, how do teams then regulate sidepod pressure? I'm glad you asked.

Exhibit B



The red arrows constitute what I'll call a "relief valve" on the exit side of the cooling system. Teams routinely add vents around the cockpit, top red arrow, when ambient temperatures require more cooling. Those vents are fed by an inlet, bottom red arrow, that's effectively behind the radiator even though it's physically beside the radiator, because the cooling flow it handles has already passed through the radiator.

The physical characteristics of the vent, its size and shape, determine the rate of air flow that passes through it, which, in turn, helps to regulate the overall flow rate of the cooling system. The overall flow rate of the cooling system determines the temperature of vented cooling air. Simply put: for any given ambient temperature, a relatively high flow-rate through the system results in cooler vented flow, because it's heated for a shorter period by the radiator, and a relatively low flow-rate through the system results in warmer vented flow, because it's heated for a longer period by the radiator.

(Incidentally, the yellow arrow points to what I think is a portion of a sealing structure that helps to seal the exit side of the system when bodywork is attached.)

For the same reasons listed above, the various vent solutions below will affect overall flow-rate. (Ignore the red arrow.)



All of these factors will contribute to Meredith's requirement for a temperature delta in the system.

Still with me? Outstanding. (Because, I'm not quite sure I'm still with me.)

Even if the effect would be the same, then still it's overall effect wouldn't match. Like Just_a_fan says; On the Mustang, the cooling system contributed to a much larger percentage of the drag created than F1 cars. F1 cars have those big, cambered wings and open wheels contributing to a much larger portion of the drag created than the cooling system.

So while on the Mustang it had a large effect on the overall drag, on an F1 car it would not.

Exhibit C



Meredith has the same effect on drag reduction as the unique sidepods found on the MP4-26, and that's why it makes sense to do it. While the cooling system of the Mustang represented a significant percentage of the plane's overall drag, the frontal area of a Formula One car's sidepods represents a signigicant portion of its overall drag. The thrust produced can virtually cancel it. Plus, you can use it to blow the edge of the diffuser to increase underbody aero efficiency.

Again, a gain of even 0.1 to 0.2 seconds makes this whole thing a grand slam in F1.

[flyboy2160]

...And flyboy, how is it that you put this idea in my head, and now I'm the one defending it, in part, from you? Is it some sort of Jedi mind trick?

Jedi Mind Tricks are part of the Trickeration and Strategery I mentioned above.

[wesley123]

The issue with the Meredith effect on F1 cars is that the cooling system contributes a small part of the overall drag, while on an plane it contributes much more to the overall drag.

Thus, while on an plane the gains on the cooling system would be significant, on an F1 car it would not. Sure, gains could be made, but I don't think they'll contribute much. The McLaren radiator package screams overcomplication(Which is something McLaren seems to love to do) while I doubt gains are actually being made.

[bhall II]

I know I'm long-winded, but you gotta read what I've written, as I've addressed that criticism directly.

It's not about reducing the impact of drag associated with the cooling system; it's about reducing the impact of drag period, and the cooling system, where Meredith just happens to apply, is the conduit through which that drag mitigation takes place.

[JimClarkFan]

I think I understand the concepts you guys are discussing in isolation, higher vents for meridth effect to reduce camber and lift, suspension to help remove air from the diffuser.

But how does the air from these two things interact because they must converge - i.e. the air exiting the vents probably interacts with the air being force up as it encounters the butterfly suspension arm? Perhaps this is why the top suspension arm has been removed, too much interference?

[flyboy2160]

I think I understand the concepts you guys are discussing in isolation, higher vents for meridth effect to reduce camber and lift, suspension to help remove air from the diffuser.

But how does the air from these two things interact because they must converge - i.e. the air exiting the vents probably interacts with the air being force up as it encounters the butterfly suspension arm? Perhaps this is why the top suspension arm has been removed, too much interference?

A minor clarification first: regardless of what happens downsteam of the radiator - Meredith Effect or not - the classic way to design an efficient radiator plenum is to allow the incoming air to expand before it gets to the radiator. As described in the Deuce's Mustang cartoon, as the velocity decreases, the pressure goes up. This drives the air through the radiator at slower than free stream velocity.

Downstream of the radiator the air is slower, but hotter. Now you can modify the exit area to give different exit velocities.

If you get the exit area Goldilocks Just Right, you can get the airspeed back up - the Meredith Effect.

But whether or not you want faster air or slower air just above the diffuser depends on your downforce and diffuser design philosophy. Scalibrini describes very well how Macca's butterfly arms create a low velocity suction area just above the diffuser in an attempt to increase the diffuser's effectiveness. Having slow velocity air exiting the body vents looks like an attempt at the same thing. This would be the opposite of the Meredith effect.

But prior to seeing these new exits, I thought I'd want the fastest, cleanest air I could get running over the top of the diffuser. It looked to me like the old RB elephant trunk exits that were well above the diffuser and Newey's ultra narrow coke bottle areas went for this. As does the current Williams body exit. I guess I still think that's the way to go, but that's purely a guesstimate. The Deuce is holding out for the Meredith Effect exits giving this increased velocity just above the diffuser.

Obviously, the real F1 engineers have the data to make much better guesses than us armchair aeroheads.

I still haven't given up my hypothesis that the extended flattened exits are for reducing sidepod camber and lift.