CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > FLOW-3D

Surface roughness

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 28, 2010, 12:45
Default Surface roughness
  #1
New Member
 
Han
Join Date: May 2010
Posts: 13
Rep Power: 15
alefem is on a distinguished road
Dear all,

about surface roughness, there is a statement on the THEORY chapter of the manual 3.3.19,

"a surface roughness provided by the user can be used as a multiplicative factor on the geometric area to increase or decrease the effective heat transfer rate. Specifying a zero roughness ,for example, eliminates the heat-structure calculation entirely, which is useful for an adiabatic boundary".
which I think means that if the surface roughness=0, there is no heat transfer happened between the wall and the fluid, is that right?

But the result does not seem right, because the default surface roughness is 0, and I still can find the wall temperature is increaseing and the temperature of the melt is decreasing.
alefem is offline   Reply With Quote

Old   May 29, 2010, 04:32
Default
  #2
Member
 
Join Date: Jan 2010
Posts: 39
Rep Power: 16
ignatz is on a distinguished road
Ale,
I see you have posted some other queries related to casting. Is this the industry you are in? If so, I don't think you need to worry about surface roughness at all.
ignatz is offline   Reply With Quote

Old   May 30, 2010, 10:54
Default
  #3
New Member
 
Han
Join Date: May 2010
Posts: 13
Rep Power: 15
alefem is on a distinguished road
Ignatz,
Yes, I am interestied in casting process.
In fact I am just testing all the manual and function of Flow3d in this stage to make sure that I will not make problem to simulate the real casting problem.

But I dont know why shoud I ignore the surface roughness, could you please give me more information?

Quote:
Originally Posted by ignatz View Post
Ale,
I see you have posted some other queries related to casting. Is this the industry you are in? If so, I don't think you need to worry about surface roughness at all.
alefem is offline   Reply With Quote

Old   June 2, 2010, 10:48
Smile
  #4
Member
 
MC
Join Date: Mar 2009
Posts: 56
Rep Power: 17
melissa is on a distinguished road
You can try using the viscous heating to model the friction that occurs in the gates due to the high speed causing sticking, if this is what you are trying to model. This just needs to be checked in the Physics tab>Heat Transfer>viscous heating.
melissa is offline   Reply With Quote

Old   June 2, 2010, 13:03
Default Possible confusion over roughness variables
  #5
New Member
 
John
Join Date: Jun 2010
Posts: 1
Rep Power: 0
jld61 is on a distinguished road
It looks like there is some confusion due to the dual usage of the term "roughness" on components. The effects of roughness on the viscous forces on a component is introduced through the variable ROUGH() which has a default value of 0.0 but it is not used in heat transfer calculations. The variable ROBS(), which defaults to a value of 1.0, should be set to account for the effects of surface roughness on the heat transfer on a
surface.
jld61 is offline   Reply With Quote

Old   June 3, 2010, 13:48
Default
  #6
New Member
 
Han
Join Date: May 2010
Posts: 13
Rep Power: 15
alefem is on a distinguished road
Thank you melissa,
And I think if the viscous heating is actived, it should work on the whole fuild field, not only on the friction boundary.

Quote:
Originally Posted by melissa View Post
You can try using the viscous heating to model the friction that occurs in the gates due to the high speed causing sticking, if this is what you are trying to model. This just needs to be checked in the Physics tab>Heat Transfer>viscous heating.
alefem is offline   Reply With Quote

Old   June 3, 2010, 13:49
Default
  #7
New Member
 
Han
Join Date: May 2010
Posts: 13
Rep Power: 15
alefem is on a distinguished road
I agree with you, there is some confusion.

Quote:
Originally Posted by jld61 View Post
It looks like there is some confusion due to the dual usage of the term "roughness" on components. The effects of roughness on the viscous forces on a component is introduced through the variable ROUGH() which has a default value of 0.0 but it is not used in heat transfer calculations. The variable ROBS(), which defaults to a value of 1.0, should be set to account for the effects of surface roughness on the heat transfer on a
surface.
alefem 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
nutRoughWallFunction and Surface Roughness Documented AlanR OpenFOAM Programming & Development 64 January 6, 2024 08:13
Surface roughness in Flow-3d Marco FLOW-3D 3 June 3, 2018 03:15
[Gmsh] Error : Self intersecting surface mesh, computing intersections & Error : Impossible velan OpenFOAM Meshing & Mesh Conversion 3 October 22, 2015 12:05
[Gmsh] Problem with Gmsh nishant_hull OpenFOAM Meshing & Mesh Conversion 23 August 5, 2015 03:09
CFX4.3 -build analysis form Chie Min CFX 5 July 13, 2001 00:19


All times are GMT -4. The time now is 06:11.