CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

2nd Order Spatial accuracy: Euler Equation on Unstrutured Grid

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

LinkBack Thread Tools Search this Thread Display Modes
Old   January 27, 2015, 05:59
Default 2nd Order Spatial accuracy: Euler Equation on Unstrutured Grid
Senior Member
Join Date: Sep 2013
Location: Hyderabad
Posts: 150
Rep Power: 11
AshwaniAssam is on a distinguished road
Hi all.

I am trying to get a second order accurate solution for the euler code on an unstructured grid. At present I am using the Green Gauss Gradient reconstruction with max-min and Venkatkrishnan limiter. I am using primitive variable formulation for gradient reconstruction on the faces. Scheme used is explicit AUSM of Liou. 2006.

For a 1-D shocktube flow problem, in the y-direction I am getting a flow with magnitude around 1, whereas for the same scheme and hexahedral grid with structured grid formulation, I was getting in the y-direction a magnitude of around 1e-3.

Because of this I suspect, that when I try to run the code for high Mach number, the code blows.

Can anyone, please help me, in implementing, 2nd order spatial accuracy on an unstructured grid, for compressible flow code.

with regards,
AshwaniAssam is offline   Reply With Quote

Old   February 7, 2015, 20:06
Senior Member
Join Date: Oct 2011
Posts: 209
Rep Power: 14
naffrancois is on a distinguished road

It is not unusual to have non-zero velocity components using non-aligned grids. The magnitude of these components should be however small compared to the main direction of the flow. Actually, as it is related to the truncation error it should decrease with mesh refinement, if it does not well there is probably something wrong. Then, you might have a problem with your gradient computation. There are many ways to check this, the very first test would be to check zero gradients for uniform flow. Then you may also test a shock tube problem in a square (or cubic in 3d) domain and change the direction of the flow.

A deeper test would also involve study of the accuracy of the gradient in an asymptotic sense, taking an exact solution from which you can extract exact gradient and compare it to the numerical gradient on a sequence of increasing grid sizes.

Don't forget that Green gauss gradients are quite inaccurate on stretched tetras if you compute the face values as an arithmetic average. Least-squares do better. But if your grid is fairly good and sufficiently refined I would not bother too much about this at this point.

Keep in mind that comparing 2nd order reconstruction on tetras and hexas will always be quite disapoiting. You will get better resolution of the rarefaction wave mainly and a slightly sharper front at the shock. It will always look better using hex, it is the price to pay

Good luck !
naffrancois is online now   Reply With Quote


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
what's faster, 2nd order eqs from the begining or 1st order and then 2nd order eqs? TimberJ3 FLUENT 0 April 1, 2014 10:08
side jet modeling for a missile: 1st order or 2nd order scheme AmirBaqa1987 ANSYS 1 March 19, 2014 05:39
Unstructured grid order of accuracy Biga Main CFD Forum 12 October 13, 2005 20:56
2nd order interpolation for NS solver Quarkz Main CFD Forum 6 July 15, 2005 22:50
Higher order discretization on staggered grid Chandra Shekhar Main CFD Forum 9 January 27, 2005 17:31

All times are GMT -4. The time now is 04:30.