Gordon Murray Automotive T.50 'rear fan'
 

Almost 30 years ago Gordon Murray designed the legendary McLaren F1, to become the ultimate benchmark for supercars for years to come. Driver sat in the middle of a three-seat configuration, carbon-fiber monocoque construction, a 627-hp V-12, six-speed manual transmission but with no ABS, traction control or power steering. It went over 240 mph and first entered & won the 24 Hours of Le Mans. Gordon Murray wanted to celebrate his 50 years in automotive engineering and created the T.50, he wants it to the be the last great 'analog' supercar. It would also have the same tri-seating configuration, naturally aspirated V-12, manual gearbox and weighing only 980 kg but he will be using his unusual aerodynamic system. He will be using the same idea in the Brabham BT46B electrically-powered fan system, which won its first & only Formula 1 race before it was banned. The T.50 uses a 48v fan to only remove dirty air from the disrupted boundary layer, not to suck the air down but to make the diffuser more efficient in creating downforce. It would have multiple adjusting valves for an auto aero mode and a high downforce mode that would assist in braking mode. It also assists with the ram induction for the engine. The 400-mm fan exhaust can also create a 'virtual longtail' that would reduce drag by 12%. The fan system's total weight would be less than adding a large adjustable rear wing and its hydraulic actuators.

https://www.youtube.com/watch?v=FSaI6STYIQA

https://www.youtube.com/watch?v=mphk-VP0chY

Gordon Murray is a genious, usually ahead of his time, but the average Joe often doesn't want to try too hard.

There was an F1 car that managed to stall the diffuser on straights to get reduced drag, not quite sure how it worked though.

I don't understand the virtual long tail? Is this a bit like that morelli tail thing?

How does stalling lower drag? Every instance I see drag is max at stall

I don't know, they lowered the car on the straights using clever suspension. Presumably increasing the pumping ratio, lowering the airflow under the car. How it works, why it works I don't know

6:34

https://www.youtube.com/watch?v=sRB9T2ACPRI

[QUOTEAeroMcAeroFace;638663]https://www.youtube.com[/url][/QUOTE]

Wow It jumped by its self?! What car is that?!?

I believe the way the T50 works is the diffuser is stalled without the fan (too steep), so that if the fan is sucking the boundary layer away, the diffuser produces both lower drag and more downforce. The car sits high enough that you can send quite a bit of air under the car without creating too much drag.

On F1 cars, I think the car is set up to pull a lot of air quickly under the car to produce high downforce at the expense of drag (ground effect is probably the main contributor). Stalling the diffuser reduces the airflow through the bottom of the car, and cuts both drag and downforce.

Haven't watched the videos, but yes the real magic is in the roof of the diffuser.

roof
 

That's my take, at least on supercars. Ferrari has flaps that lower to a less radical angle on the straights, where cornering force isn't as important, then on approach to turns, the flaps lift, increasing the ramp angle, allowing low base pressure to communicate under the diffuser. Online, there are photographs of a Lamborghini configured for this and the tufts indicate forwards airflow down and under the car, heading for the suction peak at the venturi.

That is NOT how diffusers work! In fact, it is 100 per cent wrong.

Refer to Chapter 6, Race Car Aerodynamics (Katz) - and numerous other references.

So, what does Chapter 6 say? In your own words of course.

not how
 

I advise you to take it up with Volkswagen AG, and their Lamborghini division. I didn't build the car, take the photos, or publish them. I'm just the messenger.
Tufts never lie! Right?

Perfect example of how Aerohead operates here. Is completely wrong, won't refer to references that correct his misapprehensions, continues spreading misinformation.

Just look up any reference. A diffuser does not work by "allowing low base pressure to communicate under the diffuser".

perfect
 

Is it too much to just accept information as it is. It's just information. I neither endorse nor reject reality. I just recognize reality as it's presented. It's not some grand conspiracy to spoil your party. It's about diffusers, so it's germane to the topic. Nothing more , nothing less. Please!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I guess this is why so much misinformation has been disseminated here.

To state the bleeding obvious - it is wrong information that you are spreading. Outright wrong. No nuance here - wrong.

How you say a diffuser works is simply quite wrong. So what do you do about it?

Nothing.

In your own words:
This leaves the question of how it does work as an exercise.

So much contention. People should give it a little time to play out. I follow 2-Minute Papers a lot. It's not about air, but this one on tax policy has an interesting development at 4:20: https://youtu.be/Sr2ga3BBMTc?t=260. I'm a big fan of node-based editors, they go back to the Mac Plus and are pervasive in Blender.

There exists a free tool at https://github.com/PerceptiLabs/PerceptiLabs. Any one serious about settling the question [more than I] should take a look.

No exercise is needed - just look it up.

There are literally hundreds of references that describe the basic operation of a diffuser (eg https://www.racecar-engineering.com/...-aerodynamics/). More complex explanations add vortex flow.

None of them show backwards airflow or the base pressure communicating under the diffuser.

As far as I can see, Aerohead is taking the misconceptions he applies to flow over the upper rear surface of a car (eg a notchback) and then applying them under the car in an inverted form.

In your own words: "Just look it up."

I don't understand.

Have you found a description of diffuser operation that matches Aerohead's description? I'll certainly be interested if you have.

What I'm fishing for is a description that contradicts aerohead's.

I know it isn't easy. Luigi Colani had a grasp of fluidics that I appreciate but couldn't explain.

https://ecomodder.com/forum/member-f...629-images.jpg

https://ecomodder.com/forum/member-f...644-images.jpg

I'll be blunt - Aerohead's description of how diffusers works is so ridiculous that no reference is ever going to mention his theories.

If you really want to know - and boy, am I giving you the benefit of the doubt - diffusers work like this. (And I am giving the normal workings of a diffuser, not odd ones where you suck away boundary layers, etc.)

1. They have attached flow. That attached flow, as it curves upwards, develops a low pressure.

2. That low pressure helps pull the car downwards.

3. That low pressure also helps the airflow under the car*, so giving high speed flow (and so lower pressure under a big area, so pulling the car even more downwards). *This is sometimes called 'diffuser pumping'.

4. The wake is made smaller as the airflow is directed partly upwards - just as on the upper surfaces, a fastback shape directs the air downwards. So drag can also be reduced.

5. On motorsport cars, the diffuser is much steeper and flow separates down the edges (and strakes), creating vortices. These just add to everything from 1-3, making downforce stronger but at the expense of a lot of drag.

6. There is a lot about diffusers that is not currently understood, eg diffusers work differently in drag and lift reduction on squarebacks versus notchbacks and fastbacks. The current lit suggests taking care in using diffusers for drag reduction on squarebacks.

As far as I can ascertain, Aerohead believes that lift/downforce comes from separated flow, so he assumes the diffuser is always in separated flow and it's wake pressures doing the work. But of course pressures from attached flow can be much greater than wake pressures, so no one would think that way. (Unless you'd read only a 1987 book where separation was common, of course.)

Seriously, Freebeard, if you want to learn about the topic, get away from the PC and read a book. Barnard is cheap as dirt, he is a beautiful writer and he has no major errors I have ever found.

There is a difference here between low angles used in drag reduction and high angles used for downforce:

at low angles "under-body diffuser is all about generating a pressure recovery to increase the base pressure"

"An under-body diffuser requires attached flow to enable pressure recovery"

But that is in a PhD thesis, so in aeroheads mind is completely invalid.

But in high angles, there is separation, which would lower base pressure, I don't know about backwards flow, but there is definitely separation. But the angle at which separation occurs is influenced (as always) by what occurs upstream and vorticity. And separation angle can be anywhere between 6 degrees and 30 degrees.

wrong
 

1) Science doesn't concern itself with 'wrongness.'
2) There's no such thing as too much information.
3) If certain evidence disagrees with a premise, that premise needs to be examined.
4) I beg you to illustrate where I said anything at all.
5) I simply reached into my archive and presented a reference to visual information which would qualify for ' hey, look at this- isn't it interesting ?'

diffuser and base pressure
 

1) Nature abhors a vacuum.
2) Any existing pressure differential creates a dynamic in which a 'high' will attempt to 'telegraph', 'communicate', with a 'low.'
3) The, what is typically considered, 'low' base pressure behind a vehicle, CAN be of higher pressure than elsewhere on a vehicle. An example would be a hatchback car with the hatch propped open, to allow the transport of an oversize item.
4) With the hatch open to base pressure, and a driver's side window rolled down, it's normal for engine exhaust to travel forwards through the cabin and asphyxiate the motorists with carbon monoxide, due to a low pressure caused by the A-Pillars.
5) A tunnel-effects ( ground-effects ) venturi , underneath and ahead of a diffuser, could certainly impart a suction peak ( that's what a venturi does ) sufficient enough to induce counter-flow beneath the Lamborghini. It's a physical imperative for this to happen. The orientation of the tufts would suggest that this is the case, with respect to this particular vehicle. Whether it agrees with a textbook or not.
Exceptio probat regulam. Just sayin':)

I'd already made it clear what the incorrect information was, but here it is again. You wrote:

That's my take, at least on supercars. Ferrari has flaps that lower to a less radical angle on the straights, where cornering force isn't as important, then on approach to turns, the flaps lift, increasing the ramp angle, allowing low base pressure to communicate under the diffuser. Online, there are photographs of a Lamborghini configured for this and the tufts indicate forwards airflow down and under the car, heading for the suction peak at the venturi.

Low base pressure doesn't communicate under the diffuser - that's not how diffusers work. It's similar to the idea that you have that lift is caused only by separation on the upper surfaces of cars.

I am sorry, but this is just all your theory. Maybe consult some good references on how diffusers work?

how diffusers work
 

I hear what you're saying.
The diffuser is open to a car's base. It's directly linked in both directions. High pressure will always induce flow in the direction of low pressure. Just like with separation.
If underbody flow stalls on a steep diffuser ramp, and base pressure now dominates the immediate region, if that pressure exceeds what is upstream, the air would consequently move in that direction. As in the A-pillar analogy.
There's a reason why the Lamborghini demonstrated reverse-flow. Any explanation would have to include a look at local pressures.

It's a good (free!) paper for people looking at reducing drag.

Is anyone else sick of this aggressive, unproductive, alienating, unnecessary content? Who would want to post here and have to deal with this if they post something these people think is wrong?

You seem to be consistently working under the misapprehension that validity of aerodynamic knowledge is all just at the whim of the poster. So it is "not what these people think is wrong", it is what the formal references and testing show is wrong. Big difference.

But as I say, don't believe what I (or anyone else) says. Do your own research, read aerodynamic textbooks and papers, conduct your own aerodynamic testing.

And as for unproductive, in the last few days someone has linked to an excellent free thesis on diffusers, I have given an overview of diffuser operation, someone has nominated the best and most current text on car aero, we've explored the implications of pressures and flows when optimising cooling systems - and so on.

You? Over the same period you have contributed nothing that has helped in any understanding or application of car aerodynamics.

Not aerohead. He Thanks every insult. :)

I see it as something I'm not going to be able to change. At least he doesn't threaten me with invoking the wrath of the mods, as another poster (who was eventually banned IIRC) has done to me.

Permalink pleez?

Sure I have. This sub has become a total drag. I'm trying to reduce the rhetorical turbulence and vortex of insults coming off of a certain bluff body.

I am.

I have no appreciation for the SJW approach to trying to get a point across. Totally debases their side of the argument.

Debate peacefully or STFU.

I'd take care with the SJW label. JulianEdgar isn't that and doesn't deserve it. There are more deserved criticisms.

"#post638998" = Permalink #22 above.

There should be consideration of the plenum with three 'stationary' walls and one 'moving' one. The angle and curve of the side walls is [likely] as important as the roof ceiling.

I didn't call him one. I compared the approach to being of a kind. The whole "How dare you not support my views? You're part of the problem!" followed by *bash* *bash* *bash* doesn't do anything for me.

There are parallels is all I'm getting at.

In fact, I have stated here many times:

Don't believe what I say. Go and read the current aero textbooks, read the SAE papers, do some on-road testing (eg pressure testing) and you'll soon find that a lot of what has been disseminated here is incorrect. Find that out for yourself!

Vman455 is one person here who has specifically stated that he took that advice and yes, found indeed that a lot that has been spread here is quite wrong.

You could do the same.

I have no issue with your need to correct other people's misunderstandings or limited comprehension of the subject matter. Keep doing that, if you are up for it. Correct them, point them in the right direction, ignore them if they don't take your advice.

But you don't need to put others down when they don't say or do things that are up to your standards. This isn't some snob scientist gathering, where the elitist types get to scoff and put down the new guy in the room who doesn't have the pedigree and top-tier education they were "blessed" with. It's a public forum full of amateurs trying to learn and do their best within their (limited?) abilities. There's no need to treat them as a bunch of thick-headed dolts who "just don't get it" and need to have that hammered home every time.

This is a pleasant forum because it's full of amateurs...amateurs who don't put each other down for not conforming to someone else's standards. That snobbish mentality is why I don't hang around on other car forums, where you'll get attacked if you don't install the best brand of parts or other useless drivel. It's not what I - and others - come here for, or even expect to encounter.

I'm no longer comfortable saying anything about aerodynamics, as I expect you will come in to the thread, tell me and everyone else how wrong we are (that part is fine) and then proceed to belittle us for not following your "procedures". You come off as one short step shy of actually resorting to name calling. It's not pleasant to be around. If I need to read your book and follow your procedures in order to be shown a modicum of respect, then I have no interest in sharing my fumbling attempts - which others could learn what not to do from, if nothing else - on aerodynamics here. I'll go do them quietly, on my own, and leave this place poorer for my lack of contribution.

Is that the atmosphere you wish to bring to this forum? Is that the kind of person you want to come across as?

This isn't even your thread and you're doing it.

I don't get it.

Keep up the good work with the books and videos, they're valuable to(and appreciated by) anyone and everyone who is interested. I'm sure we could all learn a lot from you.

We could potentially learn a lot more from you if we found you more approachable.

Sigh. I hate this.

Your previous post:

The whole "How dare you not support my views? You're part of the problem!" followed by *bash* *bash* *bash* doesn't do anything for me.

...was completely wrong, as I showed by pointing out that I actually suggest people don't believe me, and instead find out for themselves. (Glad to see your apology for so misrepresenting me.)

This post is equally wrong - where is your evidence that I "put others down when they don't say or do things that are up to my standards"?

You don't seem to understand the huge difference between arguing against the position a person takes, and putting someone down.

And I am a bit puzzled by the implication I am not an amateur. I am an amateur car modifier, self-taught in aerodynamics, working with limited resources from a home workshop. That's a major reason I want to see other amateurs getting the best results, not following misleading garbage.