# Step-by-Step Tutorial: Homework of Session 1

#42

Hi everyone.

During the lecture Milad mentioned something about obtaining drag and downforce values for listed velocities, so… here we go:

Notice:

• drag force consists of both pressure and viscosity forces
• downforce consists of pressure force only (due to very small values of viscous ones)
• density 1.2 [kg/m3]

How does it look like in comparison to your results?
(And why it doesn’t? I’m pretty sure it doesn’t… )

Edit:
I forgot to add that results above are for half of the wing. Below are outcomes for full wing assembly:

#43

here is a report of the results I have obtained if someone wants to compare their results: https://www.dropbox.com/sh/5w9n5px144carg9/AACaevChEOPaxwCMaXO7uIbGa?dl=0 , here is the dropbox link.
Cheers!

#44

Thanks Milad. I got the results. But what results do you expect us to submit? Do we need to make a report or something with contours plots etc. I ran the simulations for all cases and already made the submission
.

#45

Hi,

You have only to submit your simulation project using the form.

But we would for sure appreciate if you share in discuss your results in the forum

Cheers,

#46

Greetings,

I have an issue with the Forces plots with all my runs. Specifically, the Forces plots are kind of wavy (even in the final iterations) and the convergence is not really obvious.
I also get different results from the simulations on the video tutorial and i can not locate the source that leads to this difference.

Would i be possible to check what i am missing?

Regards

#47

#49

#50

Hey dude,

The forces are looking fine. What is the issue?

Cheers,

#51

I have only done the 60m/s run so far, but my plot looks exactly the same as yours. Our x and z pressure force values have overshoot and settle below the values of the tutorial. Im confused as to whats wrong as well!

EDIT: it seems most values have overshoot

#52

Ok, so – in my opinion – the problem is that Milad missed one crucial thing: Y+ values. Sometimes it just delivers inappropriate results, on the other occasion it also hampers convergence. In our case, all you have to do is to increase finalLayerThicknes to 0.9 [-]. After this change you can run all the simulations on the same mesh.

One more thing you have to remember about is drag and downforce components (!) – @aceci did that mistake in his report.

Here you have my project: https://www.simscale.com/workbench?publiclink=df1bd298-614c-4ae9-bf52-172e10dec954

Below you have graphical representation of wing regions where Y+ criterion is not met (red colour). I put in comparison between previous boundary layer setting (left) and the corrected one (right).

Pictures were taken for the highest velocity (80 [m/s]):

For the lowest velocity (40 [m/s]) it looks even worse:

Please remember: you can’t run simulation against mathematics it is driven by.

#53

@Maciek, sorry but I took into account only pressure contributions for drag and downforce running the similations with all the instructions listed in the guide and without changing anythimg…also to mee some of My results seemed to be weird in my post processing, but I Limited to report my results obtained following the tutorial. I can try also taking care of y+ and all components for the forces. Cheers

#54

My results look very similar to yours … they overshoot then settle short of the value depicted in Milad’s screen shot. The other day I looked at another person’s results that seemed to be “correct” (good convergence, matching Milad’s result) and my simulation setup seemed to be identical.

Here’s a link to my project: Results

#55

@aceci don’t worry. That’s what all these homework are for - to have a chance to make mistakes without consequences.

In terms of forces: note that for drag both pressure and viscous forces are important as the latter one is quite significant. However viscous force for downforce - comparing to the pressure one - is so small that we can ignore it.

Yplus: if you checked my boundary layer setting you would discover that for 40 [m/s] it’s still on a verge and the first layer could be a little bit higher. – Feel free to experiment with this and let me know the difference between your results and the ones I listed in one of the previous posts. I would say it’s down to this edge refinement which forced extra refinement at every single edge in the geometry.

This is how it looks like in ISOsurface:

And in colours:

Anyway, except Y+, for me the most important improvement here was force plot stabilisation.

!!! Also, your post suggested something important. Let’s try to motivate SimScale team to implement total values of forces calculated during simulations. Now we have all forces and moments listed, but in fact we have to turn most of them off to be able to see the one we are interested in the most. It would be really convenient to be able to choose what we want to follow on a chart as well as have plots for total (summarised) forces in cardinal directions. What do you think about this idea? If you like it and want to support it please give me likes, tubs up or whatever is needed to attract SimScale guys’ attention.

Problems with mesh computing
#56

Yeah sure, @Maciek I really appreciate your help. I am understanding and improving my knowledge and using such a great CAE software, I was really wondering why my values mismatched yours.

#57

Hi everybody,

while working I got the following message:
‘Cannot fetch results.’

Does anybody know why this happens?

Carlos

#58

@csanmiguel
You don’t have to worry about this message. It appears when your computer can’t get update info from SimScale server = some problems with Internet connection. In my case it happens quite often. I have a few construction sites around my house and since they started building my Internet connection experiencing regular problems. All you have to do is to ignore the message (if everything works) or refresh your browser (F5).

#59

Hello!

I have runned all 5 simulation runs but I can’t get the results.
Also, only 2 runs are labeled as finished and the other 3 are labeled as finishing up.
But I’ve recieved emails saying they’re all finished!

Here is the link to my project…

Thanks!

Bojan

#60

Thank you very much @Maciek you were right and the simulation ended without problems.

#61

The results of my simulation seem to be the same as yours: