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-   -   How t odefine head loss coefficient?pls urgent. (http://www.cfd-online.com/Forums/cfx/22070-how-t-odefine-head-loss-coefficient-pls-urgent.html)

mitesh January 20, 2006 10:12

How t odefine head loss coefficient?pls urgent.
 
I want to define darcy's friction factor in cfx?How t odefine it?Head loss=f*l*V^2/2gd.In this i want to define f.How t odefine it in cfx?second thing is that what is its relation wit hlinear and quadratic resistances in subdomain sources.Pls anybody knows then tell me. In cfx linear resistence =CR1=m/Kperm.

CR2=Kloss*density/K. Here Kperm is permeabilty coefficient.how to define this?suppose any obstruction takes 20 percent volume then is it .20.is this right or not? and what is Kloss.is it related to friction factor? I also want to know that is 2D blcoakge possible or not?IN wall we can define by thin surface.but in this there are not any variblaes related to loss coeffcient.Pls help me. Thanking you all.


Jeff January 21, 2006 13:48

Re: How t odefine head loss coefficient?pls urgent
 
There are two properties of a porous media 1. porosity 2. resistance

Until CFX-10.0, porosity was not used. Porosity is the fraction of open volume/area for fluid movement. Porosity only affects the velocity which will be seen in the porous region. (e.g. at 50% porosity, the velocity will accelerate to 2X what it is in the free streem)

The resistance affects the pressure drop through the media, and is a specific property of the media. In a packed bed it will typically be a linear function of velocity, while over large obsticles it will be a quadratic function of velocity. The total resistance (pressure drop) is modeled in CFX as a summation of a linear and quadratic term. Some media types may use one or the other or both. You have to have information on the media, such as the permiability (Kperm) or the form loss coefficient (Kloss). These are either gotten from the literature or from experimental data of pressure drop vs. flow rate for the media you are trying to model.

Hope this helps, Jeff

mitesh January 22, 2006 07:30

Re: How t odefine head loss coefficient?pls urgent
 
Thank u sir.can i apply both conditions i.e. porosity as well as resistances.


Ribeiro January 24, 2006 13:00

Re: How t odefine head loss coefficient?pls urgent
 
For sure


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