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

air flow in a tunnel

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

Like Tree1Likes
  • 1 Post By Kokemoor

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 18, 2013, 06:30
Default air flow in a tunnel
  #1
New Member
 
Tariq
Join Date: Oct 2013
Posts: 6
Rep Power: 12
Tariq Feroze is on a distinguished road
Hi all
I am a new user of fluent, i am trying to simulate air flow in a closed tunnel about 60 m long, the air is coming through a duct (50 m long 0.6m dia), i have modeled and meshed the scene in gambit.
the velocity at the exit of the duct should be 2m/s. the air will come out of the duct hit the end of the tunnel ventilate it and go out.
what boundary conditions should i use at the inlet of the duct, outlet of the duct, the end of the tunnel (if required) and the outlet of the tunnel.
when using velocity inlet boundary condition, how should i decide about the velocity specification method (component, magnitude and direction, and magnitude normal to boundary)
regards
tariq
Tariq Feroze is offline   Reply With Quote

Old   October 19, 2013, 15:48
Default
  #2
Senior Member
 
Ashwani
Join Date: Sep 2013
Location: Hyderabad
Posts: 154
Rep Power: 13
AshwaniAssam is on a distinguished road
Hi,
Do you really need a duct to be modelled. If you need a constant velocity profile you can give that at inlet of tunnel (i.e. in your case 2m/s) using velocity inlet. See help file for knowing the specification method. It is given. At outlet of tunnel you can use mostly Pressure outlet. May be with gauge pressure = 0, i.e. open to atmosphere.
AshwaniAssam is offline   Reply With Quote

Old   October 19, 2013, 18:30
Default
  #3
New Member
 
Tariq
Join Date: Oct 2013
Posts: 6
Rep Power: 12
Tariq Feroze is on a distinguished road
The air has to be delivered by the duct at a certain distance from the closed end of the tunnel, where it will strike the wall and change direction, ventilating the tunnel and go out from the opening of the tunnel. the opening of the tunnel and the inlet of the duct are on the same plane.
Tariq Feroze is offline   Reply With Quote

Old   October 21, 2013, 13:45
Default
  #4
Senior Member
 
Ashwani
Join Date: Sep 2013
Location: Hyderabad
Posts: 154
Rep Power: 13
AshwaniAssam is on a distinguished road
At the end of the duct would you like to have a constant velocity profile or a fully developed profile. From the duct you would get a constant velocity profile. Also, if you do not change the cross-section at the inlet and outlet of the duct, by continuity the velocity will be same (since, your case is incompressible one). So, You can give pressure outlet with pressure =0. While at inlet also, you should also keep pressure zero.
AshwaniAssam is offline   Reply With Quote

Old   October 21, 2013, 15:52
Default
  #5
New Member
 
Tariq
Join Date: Oct 2013
Posts: 6
Rep Power: 12
Tariq Feroze is on a distinguished road
Thanks for the response, u r really giving me company and help:-)

i got your point regarding pressure inlet and out, but what difference will it make if i do not use any velocity profile and just give any required input velocity at the inlet, the velocity at the exit will than automatically be fully developed. what difference will i get with constant velocity, ( i want the actual scenario, in actual the velocity should be fully developed).

the tunnel is very rough, i am not understanding how to cater for the roughness factor of the tunnel or even the duct, i think i am just using the no slip condition. do we have any option of specifying the material or roughness of the duct and tunnel.
what i have understood, this option is not available for all turbulent models, please guide, and where ever it is available the input required is the roughness factor, what value should i use for my tunnel (i mean how should i decide).
regards
Tariq Feroze is offline   Reply With Quote

Old   October 21, 2013, 18:17
Default
  #6
Senior Member
 
Andrew Kokemoor
Join Date: Aug 2013
Posts: 122
Rep Power: 14
Kokemoor is on a distinguished road
You have two options to control the inlet velocity profile:
First, extend your domain farther upstream so that a uniform velocity inlet will have developed by the time it reaches your real inlet location.
Alternatively, look up profiles (Section 6.6 in the Fluent User's Guide) to define your fully developed profile at the real inlet.

Regarding wall roughness: if you don't know anything about your surface characteristics, the default is probably okay. Unless your case is very sensitive to turbulence, it won't have a large effect.
AshwaniAssam likes this.
Kokemoor is offline   Reply With Quote

Old   October 22, 2013, 09:15
Default
  #7
Senior Member
 
Ashwani
Join Date: Sep 2013
Location: Hyderabad
Posts: 154
Rep Power: 13
AshwaniAssam is on a distinguished road
I am sorry, I typed tunnel instead of duct. At inlet of duct you will give constant velocity profile. And outlet of duct you can give Pressure outlet. Then you will have at exit of the duct, a fully developed flow, with avg. velocity 2m/s.
AshwaniAssam is offline   Reply With Quote

Old   January 3, 2014, 17:32
Default
  #8
New Member
 
Tariq
Join Date: Oct 2013
Posts: 6
Rep Power: 12
Tariq Feroze is on a distinguished road
for pressure outlet turbulence specification:- which method should be used and why (intensity and viscosity ratio, k and epsilon, intensity and backflow hydraulic diameter,intensity and length scale)? is the backflow hydraulic diameter the same as hydraulic diameter?
Tariq Feroze is offline   Reply With Quote

Old   January 3, 2014, 17:44
Default
  #9
Senior Member
 
Andrew Kokemoor
Join Date: Aug 2013
Posts: 122
Rep Power: 14
Kokemoor is on a distinguished road
If you expect backflow, then your turbulence specification will depend on the source of that backflow; probably the hydraulic diameter of the tunnel. If you don't expect backflow, then this won't have an effect on your final solution.
Kokemoor is offline   Reply With Quote

Old   January 4, 2014, 03:16
Default
  #10
New Member
 
Tariq
Join Date: Oct 2013
Posts: 6
Rep Power: 12
Tariq Feroze is on a distinguished road
so I should keep the intensity and backflow hydraulic diameter to zero, or use the intensity as per the velocity and use the hydraulic diameter of the exit. how should I choose amongst the available turbulence specification methods?
Tariq Feroze is offline   Reply With Quote

Reply

Tags
flow in a tunnel, tunnel ventilation, tunnel with duct

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
About Some Concepts:Laminar flow, turbulent flow, steady flow and time-dependent flow Jing Main CFD Forum 8 October 5, 2018 17:02
Simulation of air flow inside valve - FSI? Help! farianka Main CFD Forum 0 April 17, 2011 16:30
air bubble is disappear increasing time using vof xujjun CFX 9 June 9, 2009 07:59
Air flow over a cylinder - what regime? momentum_waves Main CFD Forum 6 November 19, 2008 12:08
incompressible air flow in air intake system reza besharati Main CFD Forum 4 June 4, 2001 20:23


All times are GMT -4. The time now is 00:35.