CFD Online Logo CFD Online URL
Home > Forums > Phoenics

why it doesn't abide the connuity law

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

LinkBack Thread Tools Display Modes
Old   February 28, 2001, 08:24
Default why it doesn't abide the connuity law
Posts: n/a
When I sumulate air flow around rectangle objects, I set the INLET attribute "velocity in x direction=5m/s, and in y or z direction v=0m/s". Using Ke-epsilon model, and get a converged result. But when I see the result with VR Viewer, I found the velocity near the INLET all greater than 5m/s. Then it doesn't abide the connuity law.I also find that the speed is large near the domain boundary and small in the middle in the place when x=0.[ in addition: that I set the INLET in the position of x=0]. What wrong with the result? Can anyone help me?
  Reply With Quote

Old   February 28, 2001, 16:19
Default Re: why it doesn't abide the connuity law
Arne Holdo
Posts: n/a
Hi Yj

It is good that you are very observant and study your results carefully. It is very difficult to see exactly what is wrong with your simulation from the information you give. If you are sure that the simulation has converged, then it is likely that something has gone astray with your boundary and input conditions. It is always useful to check your input conditions against a case that works. From your description a case that could be similar to yours is library case V407 which is the same as VR tutorial no 7. My first suggestion is to check your input data and boundary cnditions against those of V407.

Good luck


  Reply With Quote

Old   March 1, 2001, 06:47
Default Re: why it doesn't abide the connuity law
Mike Malin
Posts: n/a
If the run is truly converged and your boundary conditions are correct then I suspect a density mismatch. Is is possible that the density used within the domain (RHO1) differs from that employed for the boundary condition specification? Is the flow is incompressible? If so, check the ratio of predicted velocity/specified inlet velocity to see if it can be explained by an inconsistency between the inlet and field densities. Check in the RESULT file the NETT SOURCE printout of R1 for your inlet patch, i.e this records the mass flow rate in kg/s for the INLET. Divide this quantity by the inlet velocity and area, and this will confirm the inlet density used for the inlet boundary condition. In the RESULT file, RHO1= will tell you the density used for internal cells. However, if the density is variable throughout the domain you will have to store DEN1 and look at those field values to see what is used internally.
  Reply With Quote

Old   March 3, 2001, 12:16
Default Re: why it doesn't abide the connuity law
Posts: n/a
thank you for your help
  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

All times are GMT -4. The time now is 06:10.