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

WOULD YOU PLEASE HELP ME??

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 15, 2006, 00:18
Default WOULD YOU PLEASE HELP ME??
  #1
REZA
Guest
 
Posts: n/a
HI IS IT POSSIBLE TO CONSIDER THE AIR FLOW INSIDE THE WIND TUNNEL WITH THE SPEED OF 20 m/s OVER A CYLINDER AS AN INCOMPRESSIBLE FLOW? WHAT KIND OF TURBULANCE MODEL WILL GIVE A BETTER RESULTS? THANKS REZA
  Reply With Quote

Old   February 15, 2006, 04:56
Default Re: WOULD YOU PLEASE HELP ME??
  #2
MANOJKUMAR
Guest
 
Posts: n/a
IN VISCOUS SELECT K-EPSILON(2-EQUATION)
  Reply With Quote

Old   February 15, 2006, 06:56
Default Re: WOULD YOU PLEASE HELP ME??
  #3
Rajesh
Guest
 
Posts: n/a
You can calculate the Mach number of the flow from the equation M=u/c, where u is the flow velocity and c is the sound speed and is calculated as sqrt(gamma*R*temp). Normally, at room temperature, air flow at this velocity (20 m/s) has a Mach number of 0.05 ...so it can be an incompressible flow. You can consider any flow at Mach numer less than 0.3 as incompressible. Since this is a wind tunnel flow, just take care of the temperature at the test section, which is normally not the room temparture.

Also calculate the Reynolds number of the flow to determine whether the flow is turbulent. Regrading the turbulent models, have a look at the fluent manual as a fisrt step and follow the instuctions..then compare the results with standard experiments. In your case, standard K-E is a good model to start with.

All the best Rajesh
  Reply With Quote

Old   February 15, 2006, 07:16
Default Re: WOULD YOU PLEASE HELP ME??
  #4
Giuseppe
Guest
 
Posts: n/a
Hello Rajesh,

I Have the same problem; do you know the values of turbulence intensity and length scale which i have to set at the velocity inlet?

Thanks
  Reply With Quote

Old   February 15, 2006, 07:19
Default Re: WOULD YOU PLEASE HELP ME??
  #5
Rajesh
Guest
 
Posts: n/a
Are you doing the same problem with same domain and boundary conditions?
  Reply With Quote

Old   February 15, 2006, 07:27
Default Re: WOULD YOU PLEASE HELP ME??
  #6
Giuseppe
Guest
 
Posts: n/a
I have to simulate a bidimensional flow past a circular cylinder! The flow is air with temperature of about 15-20C at the velocity of 25 m/s! The domain is a rectangular domain of dimensions 25Dx32D where D is the diameter of the cylinder.
  Reply With Quote

Old   February 15, 2006, 07:55
Default Re: WOULD YOU PLEASE HELP ME??
  #7
Michael Bo Hansen
Guest
 
Posts: n/a
Never use a k-epsilon for flow over a cylinder whith no sharp edges since the k-epsilon "sticks" to much to the surface. Use a k-omega based model like the SST (Shear Stress Transport). Check this : http://www.pbase.com/michaelbo/cfd

- Michael Bo
  Reply With Quote

Old   February 15, 2006, 08:04
Default Re: WOULD YOU PLEASE HELP ME??
  #8
Giuseppe
Guest
 
Posts: n/a
the model laminar is good for this problem? if no, why?
  Reply With Quote

Old   February 15, 2006, 08:06
Default Re: WOULD YOU PLEASE HELP ME??
  #9
Michael Bo Hansen
Guest
 
Posts: n/a
What do you mean? If the flow is turbulent use a turbulence model, otherwise don't!

  Reply With Quote

Old   February 15, 2006, 08:40
Default Re: WOULD YOU PLEASE HELP ME??
  #10
Giuseppe
Guest
 
Posts: n/a
therefore, I have to calculate the reynolds number with the formula Re=density*velocity*D/viscosity, before making the simulation, to see if it is laminar or turbulence?

  Reply With Quote

Old   February 15, 2006, 09:28
Default Re: WOULD YOU PLEASE HELP ME??
  #11
Michael Bo Hansen
Guest
 
Posts: n/a
yes. Read this http://www.centennialofflight.gov/es...d_Flow/TH9.htm
  Reply With Quote

Old   February 15, 2006, 13:39
Default Re: WOULD YOU PLEASE HELP ME??
  #12
Giuseppe
Guest
 
Posts: n/a
Thanks for the link.

then is mistaken to carry out a laminar simulation with a value of Reynolds number of about 2000000?

  Reply With Quote

Old   February 15, 2006, 13:51
Default Re: WOULD YOU PLEASE HELP ME??
  #13
REZA
Guest
 
Posts: n/a
Thanks alot. Reza
  Reply With Quote

Old   February 16, 2006, 04:01
Default Re: WOULD YOU PLEASE HELP ME??
  #14
Michael Bo Hansen
Guest
 
Posts: n/a
It is highly turbulent flow at that Reynolds no.
  Reply With Quote

Old   February 16, 2006, 05:15
Default Re: WOULD YOU PLEASE HELP ME??
  #15
SAN
Guest
 
Posts: n/a
HI..everybody... I also have some problem about k-e in wind tunnel. In the k-e,it has three choice at NEAR-WALL Treatment,my Re about 25000;it has a heat sink in the wind tunnel.and which one is better for my case to use.(standard wall functions、non-equilibrium wall functions、enhance wall functions?)thanks.
  Reply With Quote

Old   February 16, 2006, 05:38
Default Re: WOULD YOU PLEASE HELP ME??
  #16
Michael Bo Hansen
Guest
 
Posts: n/a
Read the Fluent help section 11.9.1 and 11.9.2 - Michael Bo
  Reply With Quote

Old   February 16, 2006, 22:32
Default Re: WOULD YOU PLEASE HELP ME??
  #17
SAN
Guest
 
Posts: n/a
I can't find the section 11.9.1 and 11.9.2?My user's Guide only have section11.5.6.ths

  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On



All times are GMT -4. The time now is 17:39.