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

 June 10, 2005, 03:34 doubt about beta PDF #1 CH Guest   Posts: n/a Hi Dear friends, I got one probem. In non premixed LES combustion, f(mixture fraction SGS variance)) variance is assumed to be Beta distribution. I have DNS dat of the 3D reacting(non premixed) jet, I would like to compare actual PDF with the Beta PDF with my DNS data. in beta PDF calculation , I need two parameters one is f average and its variance. as i have only mixture fraction,how to get the variance? please help me Thankyou

 June 10, 2005, 04:45 Re: doubt about beta PDF #2 DES Guest   Posts: n/a In DNS you may try it with statistics.

 June 10, 2005, 05:05 Re: doubt about beta PDF #3 CH Guest   Posts: n/a Hi DES, can u please explain with more details

 June 10, 2005, 05:30 Re: doubt about beta PDF #4 DES Guest   Posts: n/a Can you please be more specific with question? What do you want to know?

 June 10, 2005, 06:30 Re: doubt about beta PDF #5 CH Guest   Posts: n/a my doubt is , I want to calculate pressumed PDF for mixture fraction..its formula is involving of mixture fraction f and its variance f',, i got f from DNS, i would like to know how to get f' in the LES cell.. i,e in DNS we are resolving the small scales,we r going to up to kolmogorov scale,then where is the question of variance again..in prior evaluation of the models for the variance, how we will get exact(DNS )variance? i hope u understood my doubt

 June 10, 2005, 09:46 Re: doubt about beta PDF #6 DES Guest   Posts: n/a I understand nothing. I am sorry.

 June 10, 2005, 10:16 Re: doubt about beta PDF #7 Salvador Guest   Posts: n/a Go back to the basics lets call Z the mixture fraction. In DNS you have Z(x,t) in very point You have to build a filter function that filtered value of Z, MEAN= 1) and the variance is VARIANCE=-^2 2) The definition of the filter function is all you need. If you assumed that the filter is a box filter basically averaging inside the LES cell of width delta (usual approach, not the most correct but the most usual without doubt) Then a function f is filtered as = SUM(f_i)/N (3) where f_i are the DNS points inside a given LES cell. N is the number of those points. The gretaer the N the better the statistics. This is teh simplest way to do it. Use (3) to compute (1) and (2) The beta PDF will depend on your MEAN and VARIANCE, and you will have a PDF in every LES cell.

 June 10, 2005, 10:20 Re: doubt about beta PDF #8 Salvador Guest   Posts: n/a Sorry the equations did not display properly [Z] indicates filtered value of Z 1) MEAN= [Z] 2) VARIANCE= [Z*Z]-[Z]*[Z] 3) [Z]= SUM(Z_i)/N In doubt check Poinsot book, or paper by Jimenez et al (2001) in Physics of fluids,

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Christoph_84 FLUENT 0 November 17, 2009 10:55 mathieu ourliac Main CFD Forum 0 April 10, 2008 05:38 Hanxsi FLUENT 0 February 26, 2006 21:51 vega Main CFD Forum 0 July 5, 2005 02:49 Liaqat Khan CD-adapco 1 October 27, 2000 04:44

All times are GMT -4. The time now is 17:44.