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-   -   Rosin Rammler Distribution (http://www.cfd-online.com/Forums/openfoam/77062-rosin-rammler-distribution.html)

mystix June 11, 2010 08:24

Rosin Rammler Distribution
 
Hallo guys,

you can define a RosinRammlerPDF at the sprayProperties of the tutorial aachenbomb (dieselFoam solver).

Does anyone knows what the parameter d defines?

I think it could be the representative diameter D0.5 = drop diameter such that 50% of total liquid volume is in drops of smaller diameter. So it would be the mass median diameter (MMD).

But I dont know for sure.. can someone help me please?

Best regards
mystix

-----------
Sorry, I wanted to post this to the OpenFOAM Forum. Can someone move this thread there?

Nam June 11, 2010 19:17

I believe this is the mean diameter of the particles.

mystix June 14, 2010 05:58

The Problem is that changing d to lower values (60Ám to 20Ám) results in a shift of the maximum to the right at a PDF-Histogramm:

time after injection 1000ms:

d=60Ám
http://mystix.lima-city.de/64.png
d=20Ám
http://mystix.lima-city.de/68.png

I would like to know how the RosinRammler Distribution works in OF. Do I define the distribution of parcels at the starting and how can I controll it?

jurich June 14, 2010 11:00

Hello,

There are source files for a Rosin Rammler pdf in the directory src/thermophysicalModels/pdfs/RosinRammler. I didn't trace the dependencies to be certain if this is called by dieselFoam, but it seems likely. It might offer you more information.

CYMa August 23, 2010 08:18

The Rosin-Rammler distribution is frequently used to describe the particle size distribution of powers of various types and sizes. The function is particularyly suited to representing particles generated by grinding, milling and crushing operations. The conventional Rosin-Rammler function is described by http://www.codecogs.com/images/eqns/...2f4a01d6c7.gif(1)

where R is the retained weight fraction of particles with a diameter greater than D, D is the particle size and http://www.codecogs.com/images/eqns/...1634e5fc00.gif is the mean particle size, and n is a measure of the spread of particle sizes. The Cumulative Distribution Function (CDF) is therefore http://www.codecogs.com/images/eqns/...1e7dcfe55a.gif(2)

As an additional note, the PDF is: http://www.codecogs.com/images/eqns/...7151fb185d.gifParameters:

Dmmean particle diameternmeasure of the spread of particle sizesDparticle size

mystix August 23, 2010 09:12

Thank you for answer, CYMa.

I agree, that the cumulative distribution rosin rammler function is right. :)

But I found in

J. Madsen
Computational and Experimental Study of Sprays from the Breakup of Water Sheets.
Dissertation, Faculty of Engineering and Science, Aalborg University, 2006.

Page 207,

that the probability density function is:
f(d) = \frac{n}{d_{mean} \Gamma ( 1-3/n ) } (  \frac{d}{d_{mean}} )^{n-4}  exp (- (  \frac{d}{  d_{mean}} )^n )

What is correct?
Where did you get your eq from?


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