Diffuser Confusion

[scarbs]

and finally a link by Scarbs
http://www.scarbsf1.com/diffuser.html

Jeez where did you find that old link! That was written about eight years ago, I wouldn't treat that explanation with any seriousness...!

[vonk]

1. It is an Open system that does NOT isolate the flow within its boundaries from the environment. Instead the open space, marked in blue, allows the intrusion of ambient static pressure.

2. Because of the relatively low flow speeds in the diffuser, the ambient static pressure, communicating at the speed of sound, will permeate the entire diffuser volume.

3. Inlet and outlet static pressure will always be ambient static pressure. Therefore, regardless of its roof shape, no “suction” can be generated at the diffuser inlet.

4. Therefore, the flow inside the diffuser will not provide any down-force.

5. With proper placement and geometry, the outside upper surface of the diffuser might be used for upward deflection of slip stream, thereby creating some down-force.

6. Strakes and other means might be use for horizontal flow deflection to aid wake management.

7. The great variety of diffuser designs seen at the races indicates that the final answer on diffusers is still evasive.

1. The air in this region is typically below ambient pressure. As flow is squeezed under the floor and in between the tires (a basic venturi or orifice), flow speed is generally increased while static pressure decreases.
That would be fine, though I see no evidence to capitalize on that on current diffusers.

2. This is untrue. It would be like saying all regions of an incompressible flow domain are iso-baric. Pressure can absolutely vary at lower than compressible speeds.
I’m saying that a turbulent flow region in an open systems is isobaric.

3. Neither are at ambient static pressure.
True for your study, which appears to be a two dimensional closed system.

4. The diffuser functions to speed up the air under the car. Note the huge increase in diffuser entrance velocity comparing ANY of the diffuser designs/angles to the simulation without a diffuser.
On an F1 car the underbody flow enters under a horizontal splitter, not under blunt body stagnation pressure. Also, you ignore the turbulent wake, created by wings and all, which is permeated by ambient pressure.

5. True. Changing the direction of flow increases pressure, therefore increasing forces (both drag and downforce)
This would not produce down-force.

[vonk]

So a brief recap of your points, vonk:
1) wrong
2) wrong
3) wrong
4) wrong
5) true but marginal
6) wrong
7) wrong
Explainations are in previous posts

Just because I don't buy your suction peaks?

[n_anirudh]

Vonk, Please refer to this wikipedia article on diffusers

http://en.wikipedia.org/wiki/Diffuser_(automotive)


Yes, the system is open,and there is bound to be leakages. If you do remember that F1 used skirts to seal the air underneath the car. Why would they even have bothered to do it if there was no high velocity flow.

...and telling others are incorrect without even having a fundamental grasp of the subject or reading their posts is just plain stupid.

Not looking forward for part2

[shelly]

So a brief recap of your points, vonk:
1) wrong
2) wrong
3) wrong
4) wrong
5) true but marginal
6) wrong
7) wrong
Explainations are in previous posts

Just because I don't buy your suction peaks?

It is not an issue of buying or not buying. Maybe you need to review some basic fluid dynamics before posting. But from you posts it seems that you have no will to learn anything.

[xpensive]

It is not an issue of buying or not buying. Maybe you need to review some basic fluid dynamics before posting. But from you posts it seems that you have no will to learn anything.

=D>

In all honesty, I think the mods should interfere when a member persists to question established and proved science.

[horse]

Look, vonk, in the simplest possible terms the diffuser is there to provide an aerodynamic shape to the car which allows it to exploit ground effect. Ground effect is proven to enhance the static pressure below a wing (high or low depending on the angle of attack).

In even more simple terms your argument that an open system can not generate a pressure difference is absurd. If this were the case planes would never leave the ground.

[mep]

I agree with the others. Vonk you should read some books about this stuff before you start to create your own theories how you think it works and confuse others with your wrong science. I am affright others even start to believe this as facts and our civilisation turns to gets even more stupid. The internet is a dangerous tool in that regards.

You have to understand the basic principle first before you can have a look at more difficult stuff. Don’t care yet about the rest of the car, the rear wing, the tires, boundary effects, kink lines or all this other stuff before you have not understand why a simple plate with a area expansion on its end can create downforce by increasing the airspeed below it.

[JohnsonsEvilTwin]

http://www.theracedriver.com/2011/06/sc ... ser-ducts/

[vonk]

In all honesty, I think the mods should interfere when a member persists to question established and proved science.

expensive,

I like your signature. But I also like mine.

I started this thread because I felt that some of the “established and proved science” expressed on this forum and elsewhere, represents inadvertent Techno-Babble. I know this is sacrilege, but it's also not surprising, given the complexity of the subjects at hand. People without formal training in the applicable fields have no choice but to accept as established science the statements by people who “should know”, though their explanations are usually couched in popular language without proof. This leads to popular acceptance of the most plausible explanations as fundamental facts. Like mixed metaphors, they can become confusing. Thus, the title of this thread.

While speaking about fundamental facts, you know some recent posts accuse me, among other things, of a lack of “fundamental grasp of the subject”. In defense, let me say that I’ve been around a while, developing a passion for physics and hands-on work with hardware during my experience in the aerospace industry and in amateur sports car racing, where I developed and drove a number of cars as owner/mechanic. My MS in aeronautical engineering (RPI) has been helpful in this. Most of all, it has taught me to question, question, question. Yet I make mistakes. Those who don’t, please let me know how you do it.

Cheers,

vonk

[Pierce89]

In all honesty, I think the mods should interfere when a member persists to question established and proved science.

expensive,

I like your signature. But I also like mine.

I started this thread because I felt that some of the “established and proved science” expressed on this forum and elsewhere, represents inadvertent Techno-Babble. I know this is sacrilege, but it's also not surprising, given the complexity of the subjects at hand. People without formal training in the applicable fields have no choice but to accept statements by people who “should know” as established science, though their explanations are usually couched in popular language without proof. This leads to popular acceptance of the most plausible explanations as fundamental facts. Like mixed metaphors, they can become confusing. Thus, the title of this thread.

While speaking about fundamental facts, you know some recent posts accuse me, among other things, of a lack of “fundamental grasp of the subject”. In defense, let me say that I’ve been around a while, developing a passion for physics and hands-on work with hardware during my experience in the aerospace industry and in amateur sports car racing, where I developed and drove a number of cars as owner/mechanic. My MS in aeronautical engineering (RPI) has been helpful in this. Most of all, it has taught me to question, question, question. Yet I make mistakes. Those who don’t, please let me know how you do it.

Cheers,

vonk

I agree with this post, but not your others. The difuser increases in volume. This alows the air to expand and return to ambient speed and pressure, this expansion allows acceleration under the car reducing static pressure. If the turning moment off the top of diffusers was the diffusers only means of generating downforce, then why oh why would they place all the strakes inside of it. Why? to seperate areas with turbulence from areas with more laminar flow, so the turbulence doesn't slow the whole flow. Why would they need that if they weren't generating downforce from the underfloor?.

[hardingfv32]

Vonk

Provide one study or paper that supports your theory. How about a statement from someone not related to this forum?

You might be good at questions, but your are not capable of understanding the answers that are being provided. It could be your ego is stopping you from understanding.

Brian

[mep]

I am curious to see xpensives reply in regards to this context now.

[xpensive]

...
My MS in aeronautical engineering (RPI) has been helpful in this.
...

Not really sure what that is, but if it's referring to some kind of university degree, you are definetly hiding it well.

Your posts should also benefit greatly from less of what you yourself call; "techno-babble", never ever seen that much word-dropping on F1T before; bounary-layers, separation, stagnation, vortexes, slip-conditions and velocity gradients...

[vonk]

Vonk

Provide one study or paper that supports your theory. How about a statement from someone not related to this forum?

You might be good at questions, but your are not capable of understanding the answers that are being provided. It could be your ego is stopping you from understanding.

Brian

Brian

You miss my point. I have no theory. I’m trying to understand how this stuff works. Empirical assertions alone, without proof, that it works don’t help. And the studies mentioned in this thread were approximations using non-representative conditions like funneled inlet into the gap from an upstream stagnation region, instead under a splitter from undisturbed free flow. The measured pressure reductions under the bluff bodies may well have been due to boundary layer choking. Pertinent data from a car on the track would be more convincing.

You’re right about the ego problem. I’m watching that.

vonk