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

CFX Simulation Physics

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 9, 2016, 07:30
Default CFX Simulation Physics
  #1
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
Hey,

This is my first post, I am just wondering if anyone could give me a hand understanding the physics behind my model.

The album can be seen here:

http://imgur.com/a/9l1Qw

Air moving at 104 m/s at 300K is coming from the right in the mainstream.

Air moving at roughly 0.5 m/s and 150K is moving up through the bottom inlet.

This creates a cooling film to the left after the hole in the mainstream.

Could anyone explain some of the physics such as shear stress, bouyancy, eddys? and how they effect this fluid flow.

I haven't really done any aerodynamics before so I am at a bit of a loss.

Thank you in advance,

Eddie.
12366636 is offline   Reply With Quote

Old   April 9, 2016, 07:54
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,869
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
There is going to be shear on the walls due to the fluid velocity, but also shear between the fast and slow fluid. This shear will help draw the slow/cold fluid out.

Buoyancy is unlikely to be of significance here are the flow velocities are high.

Eddys: There can be large scale eddies, particularly along the interface of the fast and slow gases (Kelvin Helmholtz instability: https://en.wikipedia.org/wiki/Kelvin...tz_instability). You will also get small turbulent eddies as well, but that is probably handled by your turbulence model.
ghorrocks is offline   Reply With Quote

Old   April 9, 2016, 07:59
Default
  #3
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
Hey ghorrocks,

Thank you so much for your reply, that is very helpful!

Are there any other flow physics that you think would significantly effect this model?

Thanks,

Eddie.
12366636 is offline   Reply With Quote

Old   April 9, 2016, 08:00
Default
  #4
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
Hey ghorrocks,

Thank you so much for your reply, that is very helpful!

Are there any other flow physics that you think would significantly effect this model?

Thanks,

Eddie.
12366636 is offline   Reply With Quote

Old   April 9, 2016, 08:07
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,869
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The velocities are high enough (Mach number = around 0.3) that compressibility effects are likely to be important. So you will need to do a compressible flow for an accurate simulation.
ghorrocks is offline   Reply With Quote

Old   April 9, 2016, 08:15
Default
  #6
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
Brilliant,
Is there anything else I should take into account such as the turbulence of the flow? How the cold fluid is seperating from the surface? Or anything else for that matter.

Sorry if I'm asking stupid questions!

Thanks again,

Eddie.
12366636 is offline   Reply With Quote

Old   April 10, 2016, 07:05
Default
  #7
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,869
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You don't have to include any physics to model separations. You just need an accurate model.
ghorrocks is offline   Reply With Quote

Old   April 10, 2016, 07:09
Default
  #8
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
Okay, that's good to know.

I guess the sepration is just from the turbulence in the mainstream flow is it?
I am just interested to know what physics would effect this model, even in an experimental situation.

Thank you, you have been very helpful.

Eddie.
12366636 is offline   Reply With Quote

Old   April 10, 2016, 08:10
Default
  #9
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,869
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
If there is a separation it could be due to quite a few factors. It could be the momentum of the side jet, it could be a laminar separation bubble from turbulence transition, it could be a buoyancy effect and that is just a few, with a bit of thought I am sure we could come up with more.
ghorrocks is offline   Reply With Quote

Old   April 10, 2016, 09:05
Default
  #10
New Member
 
Eddie
Join Date: Mar 2016
Location: Great Britain
Posts: 10
Rep Power: 10
12366636 is on a distinguished road
These are all things I will have to look into.

Do you know anything about entrainment? Looking through some papers on similar problems it is something I have come across but don't really understand.

Thanks for spending your time helping a beginner!

Eddie.
12366636 is offline   Reply With Quote

Old   April 10, 2016, 19:30
Default
  #11
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,869
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Entrainment is simply the flow of one fluid inducing a flow in another fluid. In simple cases this occurs due to viscous action and/or the pressure field (ie the Navier Stokes equations).
ghorrocks is offline   Reply With Quote

Reply

Tags
ansys, cfx, eddy dissipation, physical, shear stress

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
FSI simulation in ansys cfx Arash67.m CFX 1 September 29, 2017 10:52
CFX vs FLUENT for particle tracking simulation iman ANSYS 2 August 31, 2012 21:34
nucleate boiling simulation in CFX Anil CFX 3 August 25, 2010 15:18
CFX steady simulation gharek CFX 1 April 7, 2010 19:41
Simulation of turbine cascade in CFX. Jonas Pedro Caumo CFX 0 December 9, 2006 14:54


All times are GMT -4. The time now is 08:39.