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

Fluctuating velocity

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

Like Tree5Likes
  • 1 Post By pd.iiest
  • 1 Post By nasir.iitd
  • 1 Post By nasir.iitd
  • 1 Post By pd.iiest
  • 1 Post By nasir.iitd

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 29, 2014, 05:36
Default Fluctuating velocity
  #1
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
Hi
I am working on turbulent pipe flow problems, three dimensional. I am trying to find out the values of fluctuating velocity of all three components, u',v',w'. Mean velocities inform of velocity magnitude, velocities in x,y,z directions are available but not the fluctuation parts. Please help me. Thanks in advance....
jzc likes this.
pd.iiest is offline   Reply With Quote

Old   September 4, 2014, 03:18
Default
  #2
Member
 
SHEIKH NASIRUDDIN
Join Date: Aug 2013
Location: DELHI
Posts: 52
Rep Power: 12
nasir.iitd is on a distinguished road
In 'General' window tick on transient option. Then for getting u', v' and w' you need to switch ON 'Data sampling for time statistics' option in 'Run Calculation' window for transient flow before starting simulation.
hrsptl likes this.
nasir.iitd is offline   Reply With Quote

Old   September 4, 2014, 04:55
Default
  #3
Super Moderator
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 3,395
Rep Power: 46
flotus1 has a spectacular aura aboutflotus1 has a spectacular aura about
You have several options.
You can run the case in steady-state using a Reynolds stress turbulence model to get the individual components of the Reynolds stress tensor.
Or you can perform a LES or DNS to gather information about the fluctuations.
flotus1 is offline   Reply With Quote

Old   September 4, 2014, 10:04
Default
  #4
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
Thank you all...
pd.iiest is offline   Reply With Quote

Old   September 12, 2014, 01:33
Default
  #5
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
Dear nasir i have done the simulation as per your suggestions..and now i am facing problem to collect data. from where i can get the u',v',w' etc? i am a beginner in post processing. please help me.. thanks
pd.iiest is offline   Reply With Quote

Old   September 12, 2014, 03:46
Default
  #6
Member
 
SHEIKH NASIRUDDIN
Join Date: Aug 2013
Location: DELHI
Posts: 52
Rep Power: 12
nasir.iitd is on a distinguished road
Hi Prasun,
Follow the sequence:
1. Open xy plot window
2. Mention plot direction for your case.
3 On the right of xy plot window, under Y axis function, open the first dropdown list and select unsteady statistics.
4. There after, in the 2nd dropdown list, you will find rms quantities.
5. Before opening xy plot window,
you have to define the line or surface in your domain where you want the plot using following sequence:surface>line/rake or plane>define your line/ plane with specific name.
6. This new surface will be seen in xy plot window under surfaces. select the newly defined surface and click on PLOT.
I think this may help you.
hrsptl likes this.
nasir.iitd is offline   Reply With Quote

Old   September 16, 2014, 06:01
Default
  #7
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
Thank you nasir... its help me a lot.. thanks again
pd.iiest is offline   Reply With Quote

Old   March 19, 2015, 04:27
Default
  #8
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
From fluent the RMS values of velocity fluctuation can be obtained but these are mean values(<u'^2>) how can I get fluctuation velocity (u') with time?
Thanks in adv............
jzc likes this.
pd.iiest is offline   Reply With Quote

Old   March 19, 2015, 08:59
Default Temporal fluctuation
  #9
Member
 
SHEIKH NASIRUDDIN
Join Date: Aug 2013
Location: DELHI
Posts: 52
Rep Power: 12
nasir.iitd is on a distinguished road
Hi Prasun,
If you want to calculate temporal velocity fluctuations, follow the below steps:
1. You need to define the point/points in the domain where you want to calculate the fluctuating components.
2. Then go to Monitors> Surface monitors.
3. In surface monitor panel:Name(file name)>Write(click and write the location where you want to save file)>X axis(choose flow time)> Get data every (choose time step)>Integral (you can choose vertex avg or any suitable)>Field variables(choose velocity) and then your required component>Surface(choose the point you have defined> OK.
4. Then in the directory you specified, under the file name at every time step data (instantaneous value)will be stored.
5. In FFT, there is option for subtracting mean from instantaneous quantity of temporal data.
I hope this may be helpful to you.
hrsptl likes this.
nasir.iitd is offline   Reply With Quote

Old   March 24, 2015, 07:57
Default
  #10
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
thank you nasir.. it works .. in this way i got temporal velocity fluctuations for different points.. but in my problem i have to calculate velocity fluctuations for a lots of points, so is there any option from where i can easily get values of all the points or i have to make separate surface monitor for different points? Like if I create a line or rake or something. Actually my problem is a simple pipe flow simulation, i want to get values of u',v',w' at different locations.
pd.iiest is offline   Reply With Quote

Old   March 24, 2015, 08:47
Default Fluctuations
  #11
Member
 
SHEIKH NASIRUDDIN
Join Date: Aug 2013
Location: DELHI
Posts: 52
Rep Power: 12
nasir.iitd is on a distinguished road
Hi Prasun,
Can you tell me, by getting fluctuating components of the velocity field,1. what do you want plot? 2. Plotting along axial location or diametrical location? 3. Plotting of temporal or spatial data?
nasir.iitd is offline   Reply With Quote

Old   March 25, 2015, 03:51
Default
  #12
New Member
 
Prasun Dutta
Join Date: Aug 2014
Posts: 13
Rep Power: 11
pd.iiest is on a distinguished road
Actually I want to plot total turbulent kinetic energy budget in different axial and redial direction in a pipe bend flow. Reynolds stress transport equation can be defined as:
∂k/∂t= Pk + εk + πk + Dk + Tk − Ck
where
(i) Production (Pk) = −<uiuj> ∂Ui/∂xj
(ii) Dissipation (εk) = −ν <∂ui/∂xj∂ui/∂xj>
(iii) Pressure diffusion (πk) = −1/ρ ∂(<pui>)/∂xi
(iv) Viscous diffusion (Dk) = (ν/2) ∂^2(<uiui>)/∂xj^2
(v) Turbulent diffusion (Tk) = −(1/2) ∂<uiuiuj>/∂xj
(vi) Convection (Ck) = <uj>/2 ∂(<uiui>)/∂xj
That's why i need u',v',w'

plz find the attachment for better understanding of positions where i want to obtain the values of u',v',w'.

Thanking you nasir for your help...
Attached Images
File Type: jpg Untitled_pd.jpg (49.2 KB, 36 views)
pd.iiest is offline   Reply With Quote

Old   October 20, 2020, 15:20
Default
  #13
p.1
New Member
 
Italia
Join Date: Oct 2020
Posts: 19
Rep Power: 5
p.1 is on a distinguished road
Quote:
Originally Posted by pd.iiest View Post
Actually I want to plot total turbulent kinetic energy budget in different axial and redial direction in a pipe bend flow. Reynolds stress transport equation can be defined as:
∂k/∂t= Pk + εk + πk + Dk + Tk − Ck
where
(i) Production (Pk) = −<uiuj> ∂Ui/∂xj
(ii) Dissipation (εk) = −ν <∂ui/∂xj∂ui/∂xj>
(iii) Pressure diffusion (πk) = −1/ρ ∂(<pui>)/∂xi
(iv) Viscous diffusion (Dk) = (ν/2) ∂^2(<uiui>)/∂xj^2
(v) Turbulent diffusion (Tk) = −(1/2) ∂<uiuiuj>/∂xj
(vi) Convection (Ck) = <uj>/2 ∂(<uiui>)/∂xj
That's why i need u',v',w'

plz find the attachment for better understanding of positions where i want to obtain the values of u',v',w'.

Thanking you nasir for your help...
Hi, I have to do the same thing. Could you please tell me how to do?
p.1 is offline   Reply With Quote

Old   October 30, 2022, 23:39
Default ask for help
  #14
New Member
 
Jinjun Ye
Join Date: Oct 2022
Posts: 2
Rep Power: 0
Jinjun Ye is on a distinguished road
Quote:
Originally Posted by flotus1 View Post
You have several options.
You can run the case in steady-state using a Reynolds stress turbulence model to get the individual components of the Reynolds stress tensor.
Or you can perform a LES or DNS to gather information about the fluctuations.
Hi, I would like to know how to obtain the individual components of the fluctuating velocity, under the condition of steady state calculation with the RSM model.
Thanks for your reply!
Jinjun Ye is offline   Reply With Quote

Old   October 30, 2022, 23:43
Default
  #15
New Member
 
Jinjun Ye
Join Date: Oct 2022
Posts: 2
Rep Power: 0
Jinjun Ye is on a distinguished road
Quote:
Originally Posted by pd.iiest View Post
From fluent the RMS values of velocity fluctuation can be obtained but these are mean values(<u'^2>) how can I get fluctuation velocity (u') with time?
Thanks in adv............
Hi, I would like to know how to obtain the RMS values of velocity fluctuation, in the steady state using the RSM model.
thanks
Jinjun Ye is offline   Reply With Quote

Reply

Tags
fluctuation velocity, turbulent flow

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
Problem with assigned inlet velocity profile as a boundary condition Ozgur_ FLUENT 5 August 25, 2015 05:58
Velocity profile disturbance due to loss coefficient rks171 Main CFD Forum 3 May 25, 2012 18:30
LES : fluctuating velocity algorithm Frank FLUENT 0 February 5, 2006 04:54
HOW to GET FLUCTUATING VELOCITY COMPONENT at FLUEN Seyfettin FLUENT 2 December 1, 2005 04:51
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 10:11


All times are GMT -4. The time now is 07:13.