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

Melting ice - Sudden phase change of entire interior

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 8, 2019, 07:10
Default Melting ice - Sudden phase change of entire interior
  #1
New Member
 
Emil Helgren
Join Date: Feb 2019
Posts: 7
Rep Power: 7
emilhelgren is on a distinguished road
I'm trying to model the melting of a piece of ice next to some water using the melting/solidification model. I've attached the model ("Model") so you can see where the ice is and where the water is (of course, the whole rectangle is meshed even though it doesn't show). The goal is to get something that makes sense and looks right, and then i will change properties and layout and so on to be more realistic later.

I'm getting wierd results that i will explain at the bottom, but if you're interested here's first how i set up everything:

I am doing a transient study with gravity applied.
I defined a "ice-water" material with the properties of liquid water using boussinesq density. I also defined the latent heat, and i set T_liq = 270K and T_sol = 272K just to "give it some play". For boundary conditions, the edges of the ice block are adiabatic, and there is a 0.1kg/s mass flow in from the bottom edge of the water and out from the top - as if water is rising up - at 300K. The left edge is specified shear = 0 and also 300K. I initialized using hybrid initialization and patched the water interior at 272K, and the ice at 268K.
I changed Energy URF to 0.75 and liquid-factor URF to 0.2, because i was getting floating point error with the default values (is this even the best way to fix that problem?). My timestep is 0.1 and i have max 10 iterations per timestep.

RESULTS:
when i do mass-fraction contour at 20 sec ("time_20"), i see the result i expected, the water slowly melts away at the ice. But at 30 sec ("time_30"), there is a sudden phase change for the entire ice region!?
I also attached the temperature contoures at 20 ("temp_time_20") and 30 ("temp_time_30") sec, where it's very clear something is wrong as well. Do you have any ideas what i'm doing wrong and what might be causing this problem?
Attached Images
File Type: png Model.PNG (16.0 KB, 10 views)
File Type: png temp_time_20.PNG (62.8 KB, 8 views)
File Type: png temp_time_30.PNG (81.7 KB, 8 views)
File Type: png time_20.PNG (45.0 KB, 7 views)
File Type: png time_30.PNG (43.1 KB, 6 views)
emilhelgren is offline   Reply With Quote

Old   May 16, 2019, 12:30
Default Answer
  #2
New Member
 
Emil Helgren
Join Date: Feb 2019
Posts: 7
Rep Power: 7
emilhelgren is on a distinguished road
Just wanted to note to anyone interested that when i changed from SIMPLE to PISO and from second order pressure to PRESTO! i stopped getting this problem.

ANSYS recommends PISO for transient analysis and PRESTO! when there is large changes in momentum source/sink, which is very much present when using enthalpy-porosity method of modelling phase change, so i attribute the error to that.
emilhelgren is offline   Reply With Quote

Reply

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
Phase Change in VOF Evaporation/Condensation Models yoshiurr STAR-CCM+ 3 March 21, 2019 08:12
Melting Phase Change Materials sa har Main CFD Forum 0 July 21, 2018 03:08
Simulation of Phase change material (PCM) and nanoparticles together farah Main CFD Forum 0 November 2, 2015 15:30
Solid/liquid phase change fabian_roesler OpenFOAM 10 December 24, 2012 07:37
help needed about phase change Yanhu Guo Main CFD Forum 4 January 24, 2001 00:16


All times are GMT -4. The time now is 07:24.