SimScale CAE Forum

Weird Numbers for forces and moments

#1

Greetings

I was simulating incompressible flow for some f1 in schools car models with the same settings however the sixth model which i simulated racked in some weird numbers for pressure forces which were too big in comparison with other numbers that the other model racked in( for example the first model had a pressure force on the z axis of -0.452 whilst this model had a pressure force on the z axis of 62.49 on the latest iteration). I checked my mesh and the numerics,the boundary conditions they were exactly the same.So i need your help in figuring out my mistake.

Here is the link for the project: https://www.simscale.com/projects/ccharalambous/f1_in_schools-edge/

Kind Regards and thanks in advance,

Charalambos

#2

Hi Charalambos!

First of all your domain is way too small to create useful results. Also the mesh settings can be refined adding some layers to it. Let’s see what our @CFD-SQUAD has to add here.

Best,

Jousef

#3

Thanks for the advice .As for the mesh i know its quite coarse however i need to update to a better plan in order to have the capacity to mesh better

#4

Hi @ccharalambous

@jousefm sir is absolutely correct regarding the domain size, you should increase the size of your domain. Simulating with this domain will give you meaningless results. Also, I can see that total number of faces with wall B.C. are different in the first(729 faces) and last simulation(723 faces), any specific reason?

Thanks
Ani

#5

Hey,

The difference in faces is probably due to changes that i made to the design. About the faces for the first model with wall there were 735 and for the second 729.

Kind Regards,

Charalambos

#7

Hi @ccharalambous !

I agree with @jousefm & @anirudh2821998’s observations. As a topological example for wind turbines you could do the following.

1.- You could resolved in a computational domain representing the surface boundary layer (SBL) with a length of 30D in the axial direction, 25D downstream and 5D upstream of the object. You can considerer width of the domain is 7D and the height is 5D.
2.- The D value is a characteristic length, I think you could consider a D equal to the width of the object.
3.-Also, I think that in your boundary conditions you could consider the following: inlet & oulet (OK), bottom (wall), right and left walls (empty), top (atmosphere).

Best !

#8

@ccharalambous: For external CFD simulation I would expect that you put your ‘Material Point’ outside your geometry. Currently it is inside ‘solid_7_face_5’.

Cheers,

Retsam

#9

Hi @Retsam sir

I remember @ccharalambous has already set external meshing option in the hex automatic mesh settings so according to me, there is no issue with the material point.

Thanks
Ani

#10

Greetings

Thank you all for your suggestions and for the time you took to help me!