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I deal a lot with incompressible fluids and venturi devices, and a diffuser appears to be nothing more than the diverging cone of a Venturi. Every Venturi has a straight slope with an abrupt change; you will never see a venturi with a curved cone. It isn't because they can't be fabricated. So while I agree a smooth transition makes sense, data doesn't always agree with what I think it should show. Or perhaps it works better, but simply isn't worth the effort?
I also know with 2-stroke pipes, the diffuser also needs to be an abrupt change. However temperature most likely is a factor here (related to compressibility).
I could purchase one and do some low-tech testing. However I have to think the market would be higher if the manufacturer did some low-tech testing as they have the product in hand. Unless of course it is simply an aesthetic device; but if that were the situation this site would suffer the same fate as clubroadster...
Dude.
A venturi is a device for measuring a pressure difference, not reducing drag; 2 completely different applications of fluid mechanics. A diffuser in a pipe is not serving the same purpose; that kind of diffuser is supposed to slow flow down and increase pressure; exactly the opposite of what this diffuser is trying to accomplish. Abrupt changes in external geometry ALWAYS induce drag by creating low pressure regions at the corner. To minimize drag, you want the flow to stay laminar at the boundary layer as much as possible, hence smooth changes in geometry.
Same word, but two completely different things.
That being said, the drag vs speed curve is exponential, meaning a diffuser is only going to make a significant difference above a certain speed. For a Miata, I don't know what speed that is, but I would be surprised if it makes that much difference at the 80-90 mph top speed that a Miata on a road course is going to see.
R_Theory:
The CFD graphic is very nice, but there's nothing to compare it to. Even if your CFD can't produce accurate absolute value results, it would still be interesting to see the comparative improvement over the baseline analysis. Also, I would show comparative analyses at several wind velocities so you can get an idea of when the diffuser actually becomes useful.
The CFD graphic is very nice, but there's nothing to compare it to. Even if your CFD can't produce accurate absolute value results, it would still be interesting to see the comparative improvement over the baseline analysis. Also, I would show comparative analyses at several wind velocities so you can get an idea of when the diffuser actually becomes useful.
You certainly bring up some valid points, thank you for that. I've been spending the last few days tweaking the design to provide better surface attachment and I'll post the final results. I'll post up some baseline vs diffuser tests either on the facebook page and/or here.
can this v3 be paired with the v2 sides to widen it?
Unfortunately it cannot. V2 and V3 are entirely different.
Originally Posted by vtjballeng
I just threw a deposit down, I'm in. How many people are in? Curious if we hit 20+ for the $275 price break.
We did hit the 20+ mark! I am beginning production on Monday, so I decided to extend the group buy deadline to Sunday. So if anyone else is on the fence, you still have time to sign up!
Full size pics of what I received. One side was banged up which isn't the worst thing in the world. The packaging seemed careful to guard the middle but not edges. Not worrying about that.
The construction is riveted members. The downside here is that the as designed construction, while simpler to make, has significant leakage. Imagine seeing an airplan wing with holes along the chord...
Other than the as shipped damage and construction flaw, it looks nice .
For anyone who can't construct their own, I'd recommend a secondary material layer or caulking the holes. It won't be as pretty but will help. In my case, we will just end up making another one in house.
Yeah my packaging job was pretty sub-par as well. Forward mounting tabs were pretty mangled, and both of my outside "fins" were folded inward. Managed to straighten it all out enough to install though. I feel like it doesn't go out from the back of the car nearly as much as the original example pictures showed. I'm pretty not-sold on the overall effectiveness of this, even in conjunction with a flat underbelly.
I can work with it. I'll work on flat bottom things, and i'm considering making a homebrew thingy on each side to compliment it, because it's not looking good for my rear bumper cover at this point.
Once i'm happy with how it all comes together, i'll make a copy of this thing, just shove it out a good 12-16".
I'm not mad i paid for it, i'm just reasonably sure it's nothing more than drifter hotboi swag.
I can work with it. I'll work on flat bottom things, and i'm considering making a homebrew thingy on each side to compliment it, because it's not looking good for my rear bumper cover at this point.
Once i'm happy with how it all comes together, i'll make a copy of this thing, just shove it out a good 12-16".
I'm not mad i paid for it, i'm just reasonably sure it's nothing more than drifter hotboi swag.
LOL. Just don't make your revision porous as constructed here. I'll be doing the same.
Full size pics of what I received. One side was banged up which isn't the worst thing in the world. The packaging seemed careful to guard the middle but not edges. Not worrying about that.
The construction is riveted members. The downside here is that the as designed construction, while simpler to make, has significant leakage. Imagine seeing an airplan wing with holes along the chord...
Other than the as shipped damage and construction flaw, it looks nice .
For anyone who can't construct their own, I'd recommend a secondary material layer or caulking the holes. It won't be as pretty but will help. In my case, we will just end up making another one in house.
Originally Posted by concealer404
Yeah my packaging job was pretty sub-par as well. Forward mounting tabs were pretty mangled, and both of my outside "fins" were folded inward. Managed to straighten it all out enough to install though. I feel like it doesn't go out from the back of the car nearly as much as the original example pictures showed. I'm pretty not-sold on the overall effectiveness of this, even in conjunction with a flat underbelly.
I can work with it. I'll work on flat bottom things, and i'm considering making a homebrew thingy on each side to compliment it, because it's not looking good for my rear bumper cover at this point.
Once i'm happy with how it all comes together, i'll make a copy of this thing, just shove it out a good 12-16".
I'm not mad i paid for it, i'm just reasonably sure it's nothing more than drifter hotboi swag.
Thank you both for your comments. If I remember correctly one of you emailed me regarding your shipping issue. Whether it's on a forum or through email I appreciate feedback and see it as an area to improve in. Although with one of those diffusers, the condition it arrived in is unacceptable and would have been eligible for having either damaged parts replaced or more likely a new unit shipped out had I known. Feel free to email me if you would still like to have it done.
Regarding the design, your input is noted and I'll take it upon myself to revise the design for future units. Especially to make it less porous. While I currently have my hands tied with other development, i'll make it a priority to improve on those points. Once I have significant news about the new revision I'll create a new thread in my vendor section along with any relevant data and post the link here.
About the confusion between the original pictures and actual production unit and the distance they stick out past the car, the overall footprint of the production unit is unchanged from the prototype unit.
For future reference if anyone ever has an issue with shipping, please reach out to me via email and I'll sort it out ASAP. Help me help you! My focus is to provide you folks with quality performance orientated parts. Once revisions are made, i'll see what I can do to apply those revisions to existing V3 units. Any other questions or concerns please reach out to me here or via email at rtheorymotorsports@gmail.com.
The distance sticking out thing may just be context. Example pics were on an NA with a bumper, i have an NB and i'm unsure how much bumper cover i'll be able to run on this car, for other reasons shown in the pictures. Like i said, i'm not mad i paid for it, and the shipping wasn't a big deal. I was able to straighten it out.
For future shipping feedback: The box needs to be packed much more densely. My box contained the diffuser with a single layer of the small bubble wrap around it, and 2 pieces of brown paper loosely wadded up. There were no provisions to keep the diffuser from moving around within the box, and by volume, i'd say less than 20% of the box was actually occupied.
Interested to see what revisions you come up with! (Can we make this bigger? Like... a good foot bigger? )
Also, any progress on the panel you were working on to go in front of this?
08-10-2017, 12:19 PM
2
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(Can we make this bigger? Like... a good foot bigger? )
