# XFLR5 vs CFD
**URL:** https://www.simscale.com/forum/t/xflr5-vs-cfd/82854
**Category:** Using SimScale
**Created:** [July 29, 2018, 8:53pm UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854 "2018-07-29T20:53:21Z")
**Posts on this page:** 6
**Page:** 6
### Author:  [@DaleKramer](https://www.simscale.com/forum/u/DaleKramer)
#### Post date: [August 7, 2018, 7:57pm UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/101 "2018-08-07T19:57:51Z")
Thanks Jousef but darn, I thought we were resolving the viscous boundary layer by layering the mesh. How do I directly resolve the viscous sublayer so I can see the separation?
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### Author:  [@DaleKramer](https://www.simscale.com/forum/u/DaleKramer)
#### Post date: [August 8, 2018, 7:17am UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/102 "2018-08-08T07:17:21Z")
> [@1318980](#):
>
> . When I view your project, it says you saved every 1s,
I finally figured how write control got changed to 1s and then why it just hung around 💡💡
When I was playing around with making 1s simulations trying to see yPlus ranges I must have HAD to do it, just so I could get the sim to run.
And actually it was even worse than that, I did not realize that the \>Details below ‘Write Control’ input box was a dropdown to a variable (I thought it was a heading for the parameters that followed), so the only way I could get a 1s simulation to run was to change Write control to ‘Adjustable runtime’ and that automatically changed the hidden ‘Write Interval’ value to 1s… 🤨🤨🤨
I just did not realize the consequences of doing so back then… (but I did not seem to consistently get Out of Memory errors, just hang-ups). BTW, no hangups 🙂 since I have seen the light and put write back to length of sim (which BTW I have been running lengths at 400s lately, I figure if not converged at 400s, why go to 1000s).
And then it just hung around since I have been duplicating simulations to act as a template just so I don’t enter everything again. Maybe there needs to be various ‘templates’ for simulations that you can save and rename 😉
What would ever be the reason to have a sim ‘step’ at anything but 1s?
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### Author:  [@1318980](https://www.simscale.com/forum/u/1318980)
#### Post date: [August 8, 2018, 9:32am UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/103 "2018-08-08T09:32:35Z")
> [@DaleKramer](#):
>
> What would ever be the reason to have a sim ‘step’ at anything but 1s?
No scenario in a steady state simulation that I can think off, really applicable in transient simulations, where time step size makes a big difference, not only to the result accuracy but the stability of the simulation.
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### Author:  [@DaleKramer](https://www.simscale.com/forum/u/DaleKramer)
#### Post date: [August 8, 2018, 10:52am UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/104 "2018-08-08T10:52:56Z")
> [@1318980](#):
>
> [NACA0012 by 1318980 | SimScale](https://www.simscale.com/projects/1318980/naca0012/)
>
> Here is my NACA0012 project, it’s my playground for trying weird things so excuse the mess
I see that your Custom Inlet/Outlet Boundary condition also uses customized values for k=9.126000000000002e-9 and omega=0.006166216216216216 while the default values for k and omega in my Initial conditions are k=0.000001612 and omega=3.375.
To be consistent with all my other simulations in this project, I assume that I DO NOT use the values you used.
And is it sufficient to just leave them as initial conditions and not also set them in the Custom boundary condition?
Thanks Dale
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### Author:  [@jousefm](https://www.simscale.com/forum/u/jousefm)
#### Post date: [August 8, 2018, 1:29pm UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/105 "2018-08-08T13:29:37Z")
Hi @DaleKramer!
There is a SimWiki post about that topic which might be interesting for you (it is from Darren btw 🙂 ): **[Defining Turbulent Boundary Conditions](https://www.simscale.com/forum/t/defining-turbulent-boundary-conditions/80895)**
Cheers!
Jousef
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### Author:  [@andrewisaackin](https://www.simscale.com/forum/u/andrewisaackin)
#### Post date: [January 28, 2026, 9:02pm UTC](https://www.simscale.com/forum/t/xflr5-vs-cfd/82854/106 "2026-01-28T21:02:56Z")
The Whole discussions of why the Drag Values are off is this: U are comparing a Theory with CFD; XFLR5 is a theory-based solver. The Book [Fundamentals of Aerodynamics by John Anderson], In the first chapter of this book, it states the aerodynamics triangle called CFD———Theory———Experimental. So to get the best Results u compare all three from the triangle. “_Note : I am just a 1 year aerospace student, I might make some sense, or maybe I am bullshitting, please do correct me if i am wrong 🙂_“
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