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

Pressure Spectrum

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 22, 2017, 04:06
Default Pressure Spectrum
  #1
New Member
 
Amar
Join Date: Dec 2016
Posts: 7
Rep Power: 9
AmarAli is on a distinguished road
Hello everyone,

I've a simple question , and hope to check with you. I calculate the one dimensional spectra of the pressure in streamwise in channel flow from DNS. My procedure is as follows:

1) get the fluctuations p_prime(i,j,it)=p_ins(i,j,it)-p_m(k)

" For p_ins the instantenous field, p_m is the mean value at certain height from the bottom wall. (i,j,k,it) stand for (streamwsie, spanwise ,wall-normal,time), respectively.

2) get fft of p_rime ==> p_r+i p_i
3) get the spectra of E_pp(k_x)=(p_r^2+p_i^2)*(L_x/2pai) "L_x box length in x-direction"

4) Averge over spanwsie and time domains

5) check with the r.m.s of the pressure p_rms^2=Integration(-inf to +inf E_pp(k_x) d k_x ) "k_x is streamwise wave number"

However, the resulting spectrum seems to be not smooth enough. In addition the curve is little bit lower than the expected value from other studies eve if the check is correct (step # 5).

Sorry for this long explnation, but any suggestions will be appreciated.
AmarAli is offline   Reply With Quote

Old   March 22, 2017, 04:10
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,793
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
I have never worked on pressure spectrum, could you post your results?

Then, do you get good results for the velocity spectra compared to those in the database?
FMDenaro is online now   Reply With Quote

Old   March 22, 2017, 04:33
Default
  #3
New Member
 
Amar
Join Date: Dec 2016
Posts: 7
Rep Power: 9
AmarAli is on a distinguished road
Thanks for you reply,

the wall pressure spectra is attached.

Actually, I follow the same procedure in the velocity spectra and I obtained reasonable results. I guess the same steps can be applied for the pressure.

I'm sorry for this unintended mistake, Re=1000, based on the friction velocity.
Attached Images
File Type: png wall_p_cfd_online.png (5.1 KB, 16 views)
AmarAli is offline   Reply With Quote

Old   March 22, 2017, 04:39
Default
  #4
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,793
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
I don't see the plots... what about the Re number? could you post also the comparisons of the velocity spectra?
FMDenaro is online now   Reply With Quote

Old   March 22, 2017, 04:57
Default
  #5
New Member
 
Amar
Join Date: Dec 2016
Posts: 7
Rep Power: 9
AmarAli is on a distinguished road
I'm sorry for the mistake. I reloaded the pressure spectrum.

the velocity spectrum at the y^+=15 is attached in loglog scale.
Attached Images
File Type: png vel_spectrum_cfd.png (3.0 KB, 13 views)
AmarAli is offline   Reply With Quote

Old   March 22, 2017, 05:34
Default
  #6
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,793
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
I am no sure if the DNS database contains the pressure spectra, have you already checked there?

I have no experience in the pressure wavenumbers distribution for the channel flow but it seems reasonable, there is no theoretical reason to have an inertial slope like that in the velocity
FMDenaro is online now   Reply With Quote

Old   March 22, 2017, 05:53
Default
  #7
New Member
 
Amar
Join Date: Dec 2016
Posts: 7
Rep Power: 9
AmarAli is on a distinguished road
Some DNS data base provide the pressure spectra, like those of John Hopkins
http://turbulence.pha.jhu.edu/

I compared my analysis with them at the same Reynolds number and obtained a difference between the results. This makes me doubts about the methodology if it is like the velocity or not.

Pressure is expected theoretically to introduce a k-1 slope in the intertial subrange at the high Reynolds number. However, this slope was just approched in the experiments introduced by Tsuji et al. (2007), and up to now, it is not achieved in DNS.
AmarAli is offline   Reply With Quote

Old   March 22, 2017, 06:42
Default
  #8
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,793
Rep Power: 71
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
Well, could you sumperimpose your pressure spectrum and that in the database? Start with y+ corresponding to half-height channel (you wrote 1000), I do not believe you have a theoretical inertial slope close to the wall.
FMDenaro is online now   Reply With Quote

Reply

Tags
dns, spectra

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
question regarding LES of pipe flow - pimpleFoam Dan1788 OpenFOAM Running, Solving & CFD 37 December 26, 2017 14:42
Outlet pressure aja1345 FLUENT 5 August 18, 2015 11:02
Calculation of the Governing Equations Mihail CFX 7 September 7, 2014 06:27
Pulsatile pressure inlet with pressure outlet a.lynchy FLUENT 3 March 23, 2012 13:45
Sound pressure level (SPL) spectrum cfd novice CFX 0 October 12, 2008 11:15


All times are GMT -4. The time now is 16:34.