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

Space-Time correlation wind

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

Like Tree1Likes
  • 1 Post By FMDenaro

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 6, 2016, 13:14
Default Space-Time correlation wind
  #1
New Member
 
(None)
Join Date: Jul 2016
Posts: 3
Rep Power: 9
David_I is on a distinguished road
I am trying to comprehend a problem about atmospheric turbulence to which some of you may share some opinions. I have implemented a divergence-free algorithm for synthetic inlent turbulence for LES and I obtain good results for anisiotropic fluctuating time histories in Eulerian description (Huang 2010). Now I want to somehow transfer these in Lagrangian coordinates for one time instance to have the time-history basically spread out along one line of x+dx (dx=Udt with Taylor's approximation, U beeing free stream velocity) which will give me as many points in longitudinal direction as number of time steps and U'(t) would be U'(x). Now I know Taylor's approximation works only for certain frequencies only and my question is - is this right to do? And if it is, do I have a constrain on the frequency spectrum that I am simulating? I hope it is not nonsense. Thanks!
David_I is offline   Reply With Quote

Old   July 7, 2016, 04:39
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,756
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by David_I View Post
I am trying to comprehend a problem about atmospheric turbulence to which some of you may share some opinions. I have implemented a divergence-free algorithm for synthetic inlent turbulence for LES and I obtain good results for anisiotropic fluctuating time histories in Eulerian description (Huang 2010). Now I want to somehow transfer these in Lagrangian coordinates for one time instance to have the time-history basically spread out along one line of x+dx (dx=Udt with Taylor's approximation, U beeing free stream velocity) which will give me as many points in longitudinal direction as number of time steps and U'(t) would be U'(x). Now I know Taylor's approximation works only for certain frequencies only and my question is - is this right to do? And if it is, do I have a constrain on the frequency spectrum that I am simulating? I hope it is not nonsense. Thanks!

To tell the truth, I am not sure of what you want to do ....could you better explain?
David_I likes this.
FMDenaro is offline   Reply With Quote

Old   July 7, 2016, 14:30
Smile
  #3
New Member
 
(None)
Join Date: Jul 2016
Posts: 3
Rep Power: 9
David_I is on a distinguished road
Quote:
Originally Posted by FMDenaro View Post
To tell the truth, I am not sure of what you want to do ....could you better explain?
Thanks for your answer.
What I mean is: say you generate a signal U((x0,y0),t), t=i*dt with i=1:NSteps at one point with coordinates (x0,y0) with U_mean along x direction. Is it correct to say that the signal can be represented as U(x,(y0,t0)) having
at one time instance (t0) instantaneous velocity at points (x0,y0),(x1,y0),(x2,y0),(x3,y0).. (xi,y)as xi=i*U_mean*dt? In 2D this would mean a plane of a velocity field (ofc for Ux and Uy) along the mean wind direction for one time instance.

And one additional question: is anyone aware of a method computing divergence free velocity field including points along the mean velocity? Instead of points on a plane, you generate signals for points in a cube lets say. I guess
this would mean including a phase in the random signal generation.

I come from different background than CFD, and I know you can compute these type of stochastic multivariate multidimensional ergodic time histories but it does not satisfy the divergence free condition. Again, what I am asking it might be nonsense, but hopefully there is an answer.
Thanks .
David_I is offline   Reply With Quote

Old   July 7, 2016, 14:48
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,756
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Therefore, what you are asking is if at any point x0,y0 in an inflow plane z=constant is generated a problem like:

du/dt + U du/dx=0

which has the 1D solution u(x,t)=u(x-Ut,0) where U is an average velocity in streamwise direction. Right?

I doubt you can use the frozen-turbulence Taylor hypothesis ...but it is not clear to me the case you are working on... if you have an inflow plane with velocity data for the LES simulation why do you need to assume arbitrarily the values along x?
FMDenaro is offline   Reply With Quote

Old   July 7, 2016, 15:00
Default
  #5
New Member
 
(None)
Join Date: Jul 2016
Posts: 3
Rep Power: 9
David_I is on a distinguished road
Yep, it is the problem you described in 1D. So I guess you don't think its right to use the Taylor's hypothesis?

I am working with another method, not with FV - LES and trying to figure it out something which could be used for synthetic turbulence generation. Say how to compute random instantaneous turbulence field in a cube with certain statistical characteristics, rather than inflow conditions. Or even a 2D (x,y) plane in which
U_mean is along x.

I'll check it out using Lagrangian statistics, but I am quite new in here so I am not aware if the method works.

Thanks anyway!
David_I is offline   Reply With Quote

Old   July 7, 2016, 15:04
Default
  #6
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,756
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Quote:
Originally Posted by David_I View Post
Yep, it is the problem you described in 1D. So I guess you don't think its right to use the Taylor's hypothesis?

I am working with another method, not with FV - LES and trying to figure it out something which could be used for synthetic turbulence generation. Say how to compute random instantaneous turbulence field in a cube with certain statistical characteristics, rather than inflow conditions. Or even a 2D (x,y) plane in which
U_mean is along x.

I'll check it out using Lagrangian statistics, but I am quite new in here so I am not aware if the method works.

Thanks anyway!
I strongly suggest to follow the assessed technique presented in the literature. For example in this review

http://www.annualreviews.org/doi/abs...rnalCode=fluid
FMDenaro is offline   Reply With Quote

Reply

Tags
space conservation law, time discretization

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
Star cd es-ice solver error ernarasimman STAR-CD 2 September 12, 2014 01:01
AMI interDyMFoam for mixer nu problem danny123 OpenFOAM Programming & Development 8 September 6, 2013 03:34
mixerVesselAMI2D's mass is not balancing sharonyue OpenFOAM Running, Solving & CFD 6 June 10, 2013 10:34
same geometry,structured and unstructured mesh,different behaviour. sharonyue OpenFOAM Running, Solving & CFD 13 January 2, 2013 23:40
Orifice Plate with a fully developed flow - Problems with convergence jonmec OpenFOAM Running, Solving & CFD 3 July 28, 2011 06:24


All times are GMT -4. The time now is 02:38.