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

Single-species molecular diffusion does not occur with pressure-based solver

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 6, 2023, 16:00
Default Single-species molecular diffusion does not occur with pressure-based solver
  #1
New Member
 
Andrew
Join Date: Dec 2022
Posts: 29
Rep Power: 3
andrew-c is on a distinguished road
I am trying to simulate a very simple case of molecular diffusion. I have a thin rectangular domain filled with water vapor and open at the left end (pressure-outlet, with gauge pressure 0. Note that I found the same results with a pressure-inlet of gauge pressure 0, as expected). The right wall has a raised temperature, and all other walls are adiabatic. Gravity is disabled (note that this is not a simulation of natural convection).

I've enabled the species model, and I am using incompressible-ideal-gas for the density of the water vapor, along with a constant mass diffusivity and kinetic-theory for thermal diffusivity.

I expect mass flow to occur with heating, due to density changes creating a concentration gradient. However, when I use the pressure-based solver, this does not occur. Densities (and concentrations) drop on the heated end, but no mass flow occurs. Even stranger, total system mass decreases without any outflow, which appears to me as a violation of mass continuity.

On the other hand, the density-based solver shows small amounts of mass flow due to these density changes (orders of e-2 to e-4 m/s). The total system mass decreases, but the mass flowrate oscillates from positive to negative. I also find this odd because I expect primarily inflow, due to density decreasing within the domain, but I may just be thinking about it wrong.

Any ideas why the pressure-based solver is not showing these diffusion effects? If there's anything I may have missed in my setup, that may be useful to know as well.

Thanks!
andrew-c is offline   Reply With Quote

Reply

Tags
diffusion, fick law, fluent, species

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
Pressure based coupled solver for internal supersonic flow erkampasha Main CFD Forum 1 December 7, 2022 07:07
Density based compressible solver in single precision fxzf Main CFD Forum 0 April 6, 2021 19:22
Pressure based and Density based Solver Xobile Main CFD Forum 39 August 19, 2020 07:04
Pressure referencing in the rhoPimpleFoam solver? cryabroad OpenFOAM Running, Solving & CFD 0 September 23, 2019 22:51
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 16:00


All times are GMT -4. The time now is 03:28.