CFD Online Logo CFD Online URL
Home > Forums > CFX

Improving Solution

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

LinkBack Thread Tools Display Modes
Old   May 6, 2005, 15:59
Default Improving Solution
Posts: n/a
Hello All, I am doing external flow on an object to compare it wind tunnel tests, but I am off on my drag, lift and moment coefficients, any idea how I might improve mu solutions ? Thanks
  Reply With Quote

Old   May 6, 2005, 18:43
Default Re: Improving Solution
James Date
Posts: n/a

Well where do we start...

Here's a few pointers, but there are so many things to consider!

1) Which component of drag is out the most pressure (form) drag or skin friction (viscous) drag?

2) Is the mesh fine enough in the near wall region to capture the boundary layer affects and satisfy the turbulence model Y+ requirements?

3) A fine mesh in the near wall region will also help to give more accurate predictions of pressure drag and also lift.

4) Is the mesh in the wake fine enough to capture the wake coming off the body?

5) Are the far field boundary conditions placed far enough away from the body being modelled?

6) Are you applying the correct boundary conditions upstream and downstream?

7) Are you setting the correct values at the boundary conditions i.e. the same inlet flow speed and turbulence level as measured in the wind tunnel.

8) Are you modelling exactly the same flow conditions/geometry as per the wind tunnel tests i.e. are you modelling the tunnel walls correctly as no-slip boundaries? Blockage effects might also affect the predicted forces.

9) Has the simulation been allowed to run long enough i.e. down to a low residual (1.0e-06 max or machine round off)

10) Is the simulation transient thus requiring a small time step to produce good convergence?

11) Have you set the fluid properties correct i.e. the correct density, viscosity (be careful not to get dynamic and kinematic viscosity mixed up!) & fluid temperature?

12) Are you using a high order discretisation scheme?

There are many more things which could affect the accuracy of your simulation not least the accuracy of the wind tunnel measurements themselves!

  Reply With Quote


Thread Tools
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 On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Integrated conjugate heat transfer solver in OpenFOAM hjasak OpenFOAM Running, Solving & CFD 170 March 2, 2016 05:20
IcoFoam parallel woes msrinath80 OpenFOAM Running, Solving & CFD 9 July 22, 2007 02:58
solution singularity litonx OpenFOAM Running, Solving & CFD 1 February 21, 2007 02:32
Mesh independent solution CFX Begineer CFX 0 October 27, 2002 11:54
Discussion about Mesh independant solution Seb Main CFD Forum 13 May 22, 2001 13:37

All times are GMT -4. The time now is 01:18.