CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

Choice of numerical schemes for high accuracy in vorticity

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 13, 2016, 21:07
Default Choice of numerical schemes for high accuracy in vorticity
  #1
D.B
Member
 
DB
Join Date: Apr 2011
Posts: 81
Rep Power: 10
D.B is on a distinguished road
Hi All,
I am trying to simulate flow over a flat plate in icoFOAM with different BC's to suit my aim.

The Domain :

1) Uniform velocity inlet with Ux = 1, Uy = 0, obviously the flow is in X direction. It is 2D XY domain
2) The lower boundary ( constant y) is zero gradient for pressure and velocity for some initial length after the inlet.
3) After some initial length I introduce a wall(plate) with fixed velocity BC = 0 and zero gradient BC for pressure.
4) The exit boundary is zero gradient for both pressure and velocity.
5) The top (free-stream) boundary is a directionMixed boundary with Uy as fixed value and Ux as fixed gradient.

The top boundary values and gradients are given in such a way that the Z-component of vorticity is 0.

The Numerics :

1) I am running the simulation in default (double precision) mode.
2) My BC field values are specified in double precision accuracy.
3) My fvSchemes are as below

ddtSchemes
{
default Euler;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss linear;
grad(U) Gauss linear;
}

divSchemes
{
default none;
div(phi,U) Gauss linear;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default Gauss linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p ;
}


The Problem :

1) I calculate the vorticity using the 'vorticity' tool in OpenFOAM
2) What I am getting is a very large vorticity at the top boundary ( which seems to be due to the way the tool calculates the vorticity
3) In the region between the top boundary and the boundary layer edge the vorticity is reasonable but still not of high accuracy. I expect vorticity to be atleast of order of 10e-6 - 10e-7 with double precision whereas I get at very large mesh count (small cell sizes) to be at best 8e-4

I have tried different things like changing the grad schemes and laplacian schemes before vorticity evaluation but nothing seems to work.

I should also mention that my error scales directly with my velocities, so if I change my velocities to 0.1 times the value, the vorticity goes down by an order of magnitude.

I am not sure what to do, I have tried different things and nothing seems to work towards improving my vorticity accuracy. I am having my doubts on the numerical schemes, although most places it is written that Gauss linear and linear schemes are good enough choices.

Can anyone suggest what schemes should be better for improving accuracy of vorticity.
This is a simple laminar flow which should be pretty easy to get good results with. Any suggestions are appreciated.

Thanks,
D.B
__________________
-D.B
D.B is offline   Reply With Quote

Old   February 5, 2018, 11:44
Default
  #2
Member
 
Join Date: Jun 2011
Posts: 80
Rep Power: 10
maalan is on a distinguished road
Quote:
Can anyone suggest what schemes should be better for improving accuracy of vorticity.
This is a simple laminar flow which should be pretty easy to get good results with. Any suggestions are appreciated.
Hi D.B! Did you finally solve that issue? I'm at the same point as you.

Cheers,
Antonio
maalan is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
numerical accuracy Devin Main CFD Forum 6 April 28, 2004 02:22
Kinetic schemes and numerical dissipation Praveen Main CFD Forum 0 September 6, 2002 08:09
Behaviour of Numerical Schemes Ravi. B. R Main CFD Forum 3 September 22, 2001 11:18
Re: Behaviour of Numerical Schemes Ravi B R Main CFD Forum 2 September 9, 2001 05:23
Standard for checking and testing numerical schemes? X. Ye Main CFD Forum 7 August 31, 1999 18:05


All times are GMT -4. The time now is 14:59.