CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Low Speed Flow Boundary Conditions

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

LinkBack Thread Tools Display Modes
Old   March 13, 2007, 06:32
Default Low Speed Flow Boundary Conditions
Paul Bateman
Posts: n/a

This is a question from a newbie CFD user regarding a problem that really has me stumped.

I have successfully used FLUENT in the past for transonic aerofoil and wing analysis using a compressible flow setup and the coupled solver. However, I'm now trying to simulate the flow around various 2D bodies at low speeds (e.g. 10 to 30 m/s at sea level) and small angles of attack. No matter what I try I seem to get x and y velocities that converge, but mass continuity gets "stuck" at about 10e-1 or 10e-2.

The flow field looks sensible, there are no "hot spots" in terms of velocity in the domain, and lift coefficient seems sensible(ish). Mass fluxes into the domain = mass fluxes out of the domain.


"Extended D" shaped domain with aerofoil at centre.

Boundaries are at least 50 chord's away from aerofoil. ~30000 elements.

I have tried:

1) unstructured tet mesh (with high quality elements)

2) Structured quad mesh

Boundary conditions:

Front of D & bottom of D - set to velocity inlet at 30 m/s with velocity components to give 2 degree AOA.

Top of D and back of D - set to pressure outlet with a pressure of 101325 Pa normal to boundary.

Aerofoil - set as a wall.

Solution set up:

Segregated Solver.

Incompressible flow.

Energy equation disabled.

Operating pressure set to 101325 Pa.

I have tried both first and second order upwind discretisation.

I have tried inviscid, laminar and turbulent solutions.

I have tried changing under relaxation of momentum with no improvement.

I don't think the problem is to do with grid resolution because it won't run inviscid. Plus, if I set up the same mesh as a transonic problem with the coupled solver and pressure far-field boundaries it converges nicely. I think it might be my selection of boundary conditions, but I don't have enough experience to know better.

If anyone has any pearls of wisdom to offer I will happily try anything. Thanks in advance for any help offered.

  Reply With Quote

Old   March 15, 2007, 00:29
Default Re: Low Speed Flow Boundary Conditions
S Guha
Posts: n/a
Plot the mass flow values vs iteration at inlet and outlet. If it is straight (i.e. they dont have any gradients) and your mass flux report shows a difference of less than 0.5 % at inlet and outlet, then there is no necessity for decresaing your residuals i suppose. if it satisfies all these crtireion (as mentioned above) with larger residuals then it might mean it is possible......
  Reply With Quote

Old   January 10, 2013, 14:01
Default Precision
Join Date: Jun 2011
Posts: 58
Rep Power: 8
micro11sl is on a distinguished road
Are you using single precision?
Change it to double and try again...
micro11sl is offline   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
Water subcooled boiling Attesz CFX 7 January 5, 2013 04:32
1D unsteady flow boundary and initial conditions Hooman Main CFD Forum 0 August 7, 2011 06:21
boundary conditions for 2D flow around a circle abcdef123 Main CFD Forum 0 April 21, 2010 02:26
3-D Compressible Flow Boundary Conditions Tyler FLUENT 4 February 5, 2009 20:58
Boundary Conditions Jan Ramboer Main CFD Forum 11 August 16, 1999 08:59

All times are GMT -4. The time now is 20:57.