CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

Issue with Const Temp Boundary Condition for Slow Moving Fluid

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 3, 2015, 16:41
Default Issue with Const Temp Boundary Condition for Slow Moving Fluid
  #1
New Member
 
Daniel B
Join Date: Jul 2014
Posts: 20
Rep Power: 12
bgp723 is on a distinguished road
Hello,

For a project that I am working on, I am interested in doing some analysis with the local Nusselt number values over a rectangular duct.

I am simulating a simple single phase duct flow in 3D and my boundary conditions are as follows:
- uniform velocity inlet, 300K
- pressure outlet
- walls: 400K

The problem occurs when the flow is very slow, or if there are some stagnation points in the flow domain, at which the fluid temperature gets very close to the wall temperature.

In some cases, the temperature values in the fluid domain nodes are actually higher than the temperature values of the wall, though not by much 1e-5 (T_wall - T_fluid, both local values), which I assume is due to small computational errors. Of course, physically, fluid cannot be higher than the wall temperature.

These data points will noticeably throw off my local Nusselt number calculations because Nu is proportional to 1/dT. Basically, I expect to see the Nusselt number approach the fully developed value but, instead, I see Nusselt number approach the fully developed asymptotic value and then blow up after a while due to dT error. Heat flux (q'') isn't perfectly in line with the very small dT nodal points either because then the local Nu wouldn't stray off from the asymptotic value.

I was wondering if anyone have any suggestions on going around this issue, and/or methods to improve the fluid temperature accuracy.

Some additional info:

Fluid/Solid properties are temperature independent

I enabled double precision and I run the code until my convergence reaches ~ e-7 for continuity, ~e-11 for energy, and ~e-5 for other parameters of interest that I am monitoring.
I have done some mesh independence studies and I believe my current mesh is fine enough.

I extract all data I need in ASCII format and do my data analysis with the nodal point values.

For higher velocity cases, Nusselt number behaves as expected because fluid reaches the outlet before its temperature getting close to T_wall.

Thank you in advance!

Dan
bgp723 is offline   Reply With Quote

Reply

Tags
boundary condition, constant temperature, low reynolds number, nusselt number

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
[snappyHexMesh] Error snappyhexmesh - Multiple outside loops avinashjagdale OpenFOAM Meshing & Mesh Conversion 53 March 8, 2019 09:42
k-e & GAMG interFoam Schemitisation Stability Issue JFM OpenFOAM Running, Solving & CFD 3 December 1, 2015 05:58
mapFields : mpirun gives segmentation fault vanihba2000 OpenFOAM Pre-Processing 1 October 13, 2015 12:07
Wall bounded values and streamlines Ruli OpenFOAM Post-Processing 5 February 2, 2014 16:45
Parallel rasInterFoam openfoam_user OpenFOAM Running, Solving & CFD 4 November 1, 2008 04:14


All times are GMT -4. The time now is 06:48.