Flat Floor Needed for Functional Diffuser (Article Inside)
 

Found it neat to read through.. discuss?

https://www.verus-engineering.com/si...ffuser-to-Work

Thats really surprising.

Interesting.

Unless I missed it, its a pity they didn't describe the diffuser a bit more, AOA, height off the ground fron and back, length etc...

Was it a very aggressive diffuser or a very mild one like the pictures appear to indicate...

I think the article misses a trick to not be disregarded by keyboard warriors as it says its "100% untrue".
"We" have never stated a diffuser needs a flat floor simply that for it to reach its full potential i needs to be part of the floor package.
Instead of comparing something shouty folks argue about they could have given the representative changes their explanation showing that careful package creation gives better results not just slapping parts on.
They at least admit the smooth+diffuser result is likely caused by the model and would easily be better if slightly tweaked.

Just seems to try to be inflammatory with numbers than trying to show the benefits of better design.

Would a front splitter reduce the effectiveness of a rear diffuser/dirty floor because of less airflow? In other words, is the flat floor necessary for the rear diffuser to work if you have proper aero in the front?

Curious, but I wonder how much that more modern looking floor pan (flatter) compares to something designed in the late 80's (I.E. NA/NB Miata). Given the majority of their products are for more modern cars, I would suspect diffusers will work more efficiently than the NA/NB Miata. I think most of the arguments I've seen for the NA/NB application is that they work marginally, but not worth the effort/weight penalty.

That's blog post attempts to disguise itself as a white paper but it is marketing material. The company that published it is in the business of selling a diffusers for production cars without flat floors.

The repeated diatribe that you pointed out is the red flag. Marketing agenda much?

I don't agree with the methodology in the post so their conclusions are suspect in my view.


With the number of genuine, scientific method based white papers available on the web it's now common for various entities to publish their own heavily biased documents in that style. White papers are not peer-reviewed so it's sort of a gray area. Bottom line is, always take any white paper document with a grain of salt. We have talked to some of the guys at that company. Interesting bunch of gear heads like us.

The low pressure created under the splitter will feed the floor and diffuser. So a flat floor will control the airflow more letting the diffuser be more efficient. Once again the floor is not required you are just creating a situation that doesn't work well.

All of the arguments I've seen are about the gain because aerodynamics is a package deal.
Of these things work they amount they work is governed by the amount you work on the entire package.
On our rather lumpy underfloor a diffuser on its own is likely of negliable benefit without do more to control airflow to feed it up front like with a floor.

You can buy their shop car.

https://indianapolis.craigslist.org/...775397258.html

I'm not going to argue your white paper points at all. I've just seen the question posed enough times that article (with assumptions made, right or wrong) seemed relevant.

At the end of the day, we are a bunch of data driven folks here. What data means the most? Probably lap times. I've yet to see a real world comparison showing that a dirty fed diffuser is more effective than without. I'd also be curious to know impacts of a barge board setup ONLY vs barge board AND diffuser. Not seeing published results on this matter has led me to believe the diffuser isn't worth my time investment yet. By comparison, there is a ton of feedback with various spoilers or airfoil elements, splitters, and air dams making a notable lap time difference.

Having a diffuser on a car is not a goal.

I have their diffuser installed in my car, compared before and after lap times without much improvement. Looks tits af tho :bigtu:

Cameron at Dsport had a positive experience.
https://www.dsportmag.com/the-cars/n...ata-part-four/

And big shock they have a splitter, flat floor and diffuser. Marketing tat without good data comparison

With regard to most people here we've got much bigger fish to fry than a rear diffuser. And if we are adding one we are probably trying to incorporate some flat underbody at the same time. So I don't see much Point unless you're trying to sell diffusers.

If I'm reading this correctly, the smooth floor alone was better than either diffuser option.

Setup | Drag | Lift
Dirty Floor | 285.7 | 143.4
Dirty Floor w/ Diffuser | 259.5 | 133.2
Smooth Floor Only | 225.7 | 92.2
Smooth Floor w/ Diffuser | 223.6 | 101.9

On the dirty floor, the diffuser reduced drag by 10%, and reduced lift by 7%.
By comparison, the flat floor alone reduced drag by 21% and reduced lift by 36%.

Didn't read article...but based on your numbers, the diffuser only improved drag and solely by ~1% from having a flat floor and yet added ~10% in lift. Smooth floor only looks like the ticket.

If there was a proven performance benefit to it, I'd say it would be a goal to have.

Haven't found any overwhelming evidence that says there's a benefit though. My car won't have one unless I find that proof, or I get really really bored and want to build one to test myself.

No part is ever a goal.
The performance benefit is the goal.
Just like no one's goal is having a turbo for example, the goal is to have the power and powerband desired, which is why there's more than one way to skin the cat.
No one's goal is having a diffuser (save for looks, but I'm not commenting on that), it's the performance benefit that you should be after.
Can the performance benefit be justified for the diffuser in question?
Not in my book.

soooo if I'm not mistaken... we are saying the exact same thing differently. Neat.

Flat floor isn't needed on Corvettes........which have flat floors. For these kinds of answers I look to aerodynamic engineers that work for companies that don't sell parts. There is a guy who was dumping great knowledge on youtube KyleEngineers. He recently got picked up to work in F1 to give you a indication of his abilities. What we are left with is the knowledge he gave us before his leap to F1 and at the time he was working for no parts manufacturer that I knew of. Here is his opinion on flat floor required.

Even some of the best and most detailed models out there are woefully simplistic in respect to the underside of the car compared to reality. So many details are omitted that affect the flow. Then you have the evacuation of turbulent warm air from heat exchangers that is usually left out of simulations entirely. For several reasons, under-car airflow - particularly for an exposed under-body on a car a decade or older with less effort from the factory originally to smooth that airflow - is very, very difficult to simulate accurately. It's entirely unsurprising to see a simulation on a model tell a story that makes it seem that the difference between a flat bottom and no flat bottom, (and the effect of each in relation to a diffuser) is less significant than it is in reality.

Care to explain? We never tried to disguise it as a white paper. We posted it on our companies blog...which all blogs are for some marketing purposes. Does that make the work any less correct? I did these specific tests to show as data every time someone says diffusers do not work without a flat bottom as that isn't true. I thought the car would be a good test and would be good information.

The repeated diatribe aka making it readable to the average enthusiast. Eric massages my words because if I wrote it 100%, it would be unreadable to most as I am too technical and analytical.

What specific of the methodology do you have an issue with?

We are a 3 person company. Eric (owner / engineer), Clay (sales and marketing), and myself (owner / engineer). We were not trying to sell anything with that blog post. Just clear up miss-confusions that are all over the web. What is super odd is companies such as yourself (who does buy some of our products) talking trash for no reason. I didn't see any facts to disprove our testing. I just see smack talking for really no reason. We go out of our way to test and validate all of our products...I'd argue more than most. We run PROPER CFD testing to develop most of our products. We just validated some of that CFD in the wind tunnel last month with our rear wings and a few other companies wings. We also just became members of our local track so we can test all the time and plan on paying a professional driver to get back to back tests. When I say a professional driver, I mean an old Indycar driver. We dump so much of our revenue back into being able to develop better products.

For everyone else who is just curious. This wasn't meant for a be all end all. It was to show that diffusers can work and work well without a flat bottom. No need to take anything to the extreme. It doesn't mean that all diffusers will work the same and that a flat bottom will always outperform flat bottom and diffuser together. If you have any questions, I can probably answer since I did all the CFD and CAD work for this.

I will pop open the CAD tomorrow if I remember and get you these answers.

Hi Paul

That would be great thankyou. I dont want you to spill on anything you don't want to but like most here am certainly interested in what you can provide.

Of all the forums around this is one of the toughest, most critical and most serious.....it pays to have VERY thick skin if you want to be involved :) (often times, thicker than what I tend to have!) HOWEVER, a lot of incredible and normally unavailable knowledge, time, experience and research from people like Emilio, The Pass, Savington and many others gets freely shared and gven away so whilst a pretty tough place/crowd, it does tend to work pretty well if you can cope!

The fact your here to discuss is a real feather in your cap. Sadly the internet these days wll have greatful people, genuinely interested/inquistive people, argumentative people and rude people and often a mixture of all the above. Hopefully you will see more of the first few than the last few :)

AOA / car rake = 0.23 deg [should have been how the model came]
AOA / diffuser rake = 1 deg [overall diffuser angle, not the tunnel]
AOA / tunnel of diffuser angle = 5.9 degree effective from the diffuser rake itself [aka from the ground plane, it would be 6.9 deg]
Ground to throat of the diffuser = 190.7mm
Tunnel Length = 800mm
Overall Diffuser Length = 900mm
Tunnel Width = From 1000mm to 1250mm

If you would like anything else, just let me know. I am perfectly fine with critical, but all I saw was hate with no information or data to back up anything else. I am fine with people being critical since that is the best way to improve. However, the internet is full of more shit talking than constructive criticism. We did it to just show that flat floors aren't always needed which is spread across the internet like the gospel. We are pretty much as transparent with our aero work as any company out there and try to help explain more complex issues.

Data makes people here happy. So does transparency. Sharing important parameters like you did in the last post helps with the peer review of your findings, which is fundamental to the science of anything. Would you rather us be less questioning of the claims of manufacturers? Wouldn't that make us a less valuable forum? How much more valuable to you would it be if your results were confirmed independently by members here? This is why any scientist or researcher conducting a study lays bare all of his methods and data and asks others to repeat or verify his findings.

Pointing out you are a vendor with a product to sell is not a personal attack but a statement of fact. It is important to know the source of motivation or funding for any study for the sake of transparency. And having only part of the data or specifications available to us leads to predictable conjecture. Put it all out there and you will be rewarded if your information is valid.

Maybe data in here makes people happy, but we have found in the past that most of my technical output is worthless to the average consumer as they do not fundamentally know fluid mechanics or the in-depth of CFD. Does it matter to the end user if I used second order or PRESTO! for my spatial discretization of pressure? Does it matter if I used second or first order upwind? Does it matter if I fully resolve the boundary layer or use wall functions? What about turbulence models? All of these do matter, but 99%+ of people do not know what these are, and it makes their eyes glaze over. We use to show and share this type of information in our past work, but were told by many this information was not needed. Our goal wasn't a peer-reviewed paper as people can do their own work on the subject. We were just sharing our findings of work we did. Nobody could verify our findings with any of the data without us sharing our CAD and our specific setup. If I another member here COULD verify it, I would be shocked. Finding someone who can use proper CFD software is very rare. Our software cost $35,000 per year license-based and most are priced around that except OpenFOAM. I also have experience in OpenFOAM as that is what I learned on. If an independent member here has a license of Fluent and a computer that can handle a 40 million cell model, be my guest. The .msh file is around 6gb I believe. Each case takes around 12-18 hours to solve on our 20 core server setup. You will also need 128gb+ of ram most likely.

Pointing it out is okay. We assumed it was obvious as it is on a companies blog. Saying we have ulterior motives is another thing. I never posted this on here. We posted it on our company page and so our customers who already follow us can see. We do not hide the fact we are a business that sells aerodynamic components. A predictable conjecture of what? What all is missing that should be there in your opinion? It will help us provide better blogs in the future. I am assuming things like the spatial discretization is not needed. I try and cut it off where most people seem to grasp the information.

To be fair, the bolded portion was only about 25% of the 100% negative and 75% baseless post in question. Included mentioning "not agreeing with the methodology," but without any further comments regarding such. (Why? When? Who? How often? To what extent? What would be better?)

To be fair to that side as well, though.... about 99.9% of what's posted on the internet is garbage, so none of the post was really a huge leap to take.