Anyone here know how to use OpenFoam? I want to test some theory I made but I don't have a clue how to use CFD software

Anyone here know how to use OpenFoam? I want to test some theory I made but I don't have a clue how to use CFD software.

Other urls found in this thread:

youtube.com/watch?v=qTYAr8jgViM
youtube.com/watch?v=nkuawZkiu1w
gen.lib.rus.ec/
twitter.com/NSFWRedditVideo

I want you to run a simple simulation for me, I'll give you my predictions and you tell me if they match up? Can anyone do this for me?

Cmon guys don't make me have to physically do the experiment, that would cost money

What do you want to simulate?

This
youtube.com/watch?v=qTYAr8jgViM
If you could so kindly rerun the simulation at let's say a pressure jump across the actuator disc of 400 Pa, 1200 Pa, 1600 Pa and 2000 Pa, that is all. 4:25 is where he does it for 800 Pa. let me know what max velocities you get at the duct lip for each pressure. With 800 Pa he got 62 m/s. My theory got 72 m/s so maybe it's on to something I don't know.

These are my predictions where the P is the pressure jump across the actuator (propeller) disc and v is the max air velocity over the duct lip

P v

400 Pa - 51 ms^-1

800 Pa - 72 ms^-1

1200 Pa - 88 ms^-1

1600 Pa - 102 ms^-1

2000 Pa - 114 ms^-1

Not an engineer so I never used openfoam but I may give it, seems pretty neat

Thank you.

>Nice video and example. However, you mentioned that you imposed 800 pa using baffleDict, which is incorrect since if you check the units in the 0/p boundary conditions, the unit is m2/s2. Therefore, you imposed 800 m2/s2.

You sure you're not getting the right answer because whoever made the video was using the wrong units?

I got no idea I have no clue how OpenFoam works, all I can see is that judging by the colour graph of the pressure the pressure below the disk looks to be about 300 Pa and the pressure above -500 which would add up to a 800 Pa difference so it seems to check out. Anyway this is why I made the thread, if it's a single coincidence the rest of my results will be way wrong.

well it's solving but it seems like it's gonna take a while, especially if you want jumps of 400 Pa
maybe check back tomorrow?

Aww thank you so much! I really appreciate this!
Ok I'll check back later!

Finished test run at 800 Pa to compare the results on the video, got 64 instead of 62.3. I'm running a newer version of the software though

I'll be going to bed now but I'll leave the rest of the simulations running, should be done tomorrow

mmm closer to 72, so far so good. Alright see you tomorrow and again thank you!

Here's 400 Pa, got 45. Still a bit lower than your results apparently

1200 Pa
79 m/s

1600, 91

2000 Pa, 100
And we're done.

Thank you!

That is actually interesting that they're all below my prediction, strictly speaking I predicted the maximum theoretically allowed speed so I expected reality to be slightly lower

What do you think of the fit though? It seems to be about 15% out, Is that close enough to say my model works? I'm happy with it, The reason for developing it is that I want to design ducts for my RC aircraft propellers but being an amateur I don't have the skills to run fluid simulations so I made this equation from some math I learned at my local library.

Hopefully I can now use my model to work out the lift coefficient for the entire duct. I'll post that later and you tell me if the derivation makes any sense.

Nice thread.

Fuck I owe the library money, can't get the book. I'll try to find some MIT OCW notes to rederive it from. I couldn't prove it worked so I threw it away (not wasting money building aircraft based on some made up theory with zero proof) but then I ran into that OpenFOAM video which gave me a way of testing the results.

Thanks. Math coming soon.

Just the book on gen lib

Forgot about that thanks. While I get some info together to rederive it here is how I got my predictions. The first half is just momentum theory, the maximum velocity over the duct lip being four times the freestream velocity is my prediction.

I'm the guy who ran the simulations, why don't you invest a little time learning openfoam? It seems to be very relevant to what you're trying to do and it's not that hard unless you wanna write your own solvers, but you don't have to do that for sims like this one.
The hardest part seems actually making the mesh for the simulation since I used the one that came on the video, but maybe you could look into it. I mean it doesn't look THAT hard youtube.com/watch?v=nkuawZkiu1w and there are tutorials on how to use the mesh on openfoam on that same channel that you linked to, look at that guy's other videos
For the books go to gen.lib.rus.ec/ and for papers there's sci hub (google it)

Yeah, seems like your max speed is an approximation and that's where the difference from actually solving the differential equations comes from. I don't know anything about RC aircrafts so you'll have to decide if it's accurate enough for your needs

The command line thing scares me, I'm a GUI pleb. And I heard that you need to know how to solve Navier-Stokes equation and stuff to be able to use CFD. It seems to me like it's only for specialists with graduate level knowledge, as I said I'm a total amateur. Most I know is how to plug reynolds numbers into XFOIL and that was a challenge for me. Anyway I'm alturistic, I can make life easier for other hobbyists by making a simple rough equation. The ultimate goal is to find the lift coefficient of the duct lip so all you have to do to work out if your 3D printed duct is too heavy to boost your flight time is plug and chug the lift equation. It doesn't have to be exact.

Also working it out on paper is kinda fun because I'm autistic.

Has anyone experimented with actuating the duct lip itself to generate forward thrust? Like having a bunch of panels that can move independently instead of single solid ring?

Lmao I do this. I also use warm food too ;_;

That was actually a plan of mine but as the results have shown the duct lip is already providing the maximum amount of lift possible so there is no point.

It's also hard to build a variable diameter torus.

why dont you just pirate solidworks.

cause solidworks sucks for CFD

Are you sure.. it's not like openfoam is an industry standard.

that may be a good idea since it's easier to use, but bear in mind that solid's cfd capabilities are nowhere near those of openfoam
if op wants a gui then pirating fluent instead could be an option

for cfd it's more of an standard than solid that's for sure
(the actual standard is fluent)

Even Autodesk offers better alternatives for CFD than solidworks. It’s like you recommended the worst possible software for this application

Waiting to afford a better PC basically. Also wasn't sure it had GUI CFD capabilities, I had just heard rumors.
What is Fluent?
I have planned for ages to get one of them when I get a new PC because I've been using some budget hobby CAD software all this time Someone told me that Solidworks is the industry standard but now you say Autodesk has better CFD so now I'm confused as to which one to choose.

Fluent is like open foam but with a GUI and easer to use, just watch YouTube videos it’s a lot simpler. Not sure if there’s a pirates version though

Ok thanks.

Here's the derivation.

I skipped a lot because I assume you're all familiar with potential flows. Sorry that my "gamma"s and "r"s look the same

Where did everybody go? Does the derivation make sense?

Judging by the lack of claims othwerwise I'm going to assume the theory works. Thanks everyone, especially the guy who ran the simulations for me. I really appreciate that you took the time to do that for me. If I make anything cool with it I'll let you guys know.

Just an addition, I worked out the lift coefficient of the duct lip to be 16/3. Applying this to my OP image of the Hillier Flying Platform, if the propeller is providing 150 kg of thrust, the freestream velocity is 13ms^-1 and thus the 1.5 m^2 area duct lip should provide 85 kg of lift

That's 36% of the total force which checks out because details on the design state that:
>The duct also provided additional lift, since there was a horizontal "lip" around its top edge that curved down into the duct. The airflow into the duct resulted in low air pressure above the lip, and the pressure difference between the top and bottom of the lip generated a net upward force, providing as much as 40% of the total lift of the aircraft.

The only problem with ducting though is that it screws up performance.