
[Sponsors] 
April 17, 2012, 09:32 
plzzz help::energy equation using power law method

#1 
New Member
maryam
Join Date: Jan 2012
Posts: 11
Rep Power: 6 
hello every body
I am writing fortran code for 3D fluid flow in a rectangular duct. I have problem with descritising energy equation using pawer law method (finite volume). integrating viscous term is some how inpossible. one friend told me to take out that part out of integral like a constant number. is it right??????? and if it is right i have other problem descritising terms like d(u)/d(y). should i do it like what i do for momentom equation( i mean the formula used to find a(nb)) or the accsess is gained only through interpolation? thanks. sepideh 

April 17, 2012, 18:36 

#2  
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 390
Rep Power: 10 
Quote:
The temperature equations has viscous heating term = viscosity * shear rate^2 . Thats all. The viscosity is calculated based on what is currently available as best guess for temperature. Typically power law with temperature dependence would be of this form: viscosity = m * EXP(tc * (T  t0)) * shear rate ^ (n1) Where T is temperature. PS: This is not an easy calculation to do. I did last week or two ago for our company and i can tell you it is very tricky business to put into practice. 

April 18, 2012, 01:09 

#3 
New Member
maryam
Join Date: Jan 2012
Posts: 11
Rep Power: 6 
thanks arjun
but I have a problem understanding you. do you mean with integrating energy equation I will reach your last equation? what is tc and t0? i should mention that I am studying steady flow 

April 18, 2012, 03:32 

#4  
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 390
Rep Power: 10 
Quote:
There are no terms related to time in it. Tc and T0 are constant so you can use it for steady case too. In fact i also did steady calculation. 

April 20, 2012, 05:36 

#5  
Senior Member
Join Date: Aug 2011
Posts: 251
Rep Power: 7 
Quote:
Energy equation is a transport equation with a convective term , a diffusive term and sometime a source term. The power law scheme is used to discritize the convective term of the equation (one could use UDS scheme, CDS scheme etc....) The diffusive term are generally discritized using central second order finite difference. To me the both are not linked (power law scheme and diffusive term) Check Patankar' book or Versteek and Malalasekera book. Everything is perfectly explained in it. 

April 20, 2012, 08:05 

#6  
Senior Member
Arjun
Join Date: Mar 2009
Location: Nurenberg, Germany
Posts: 390
Rep Power: 10 
Quote:
O man, I completely mistook him. I thought he was asking about power law fluid with viscous heating in temperature equation. 

Tags 
energy equation, finite volume method, pawerlaw 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
CFX non newtonian power law fluid  Mehmet SORGUN  CFX  4  October 13, 2013 10:25 
Constant velocity of the material  Sas  CFX  15  July 13, 2010 08:56 
about one seventh power law in CFX  Eric  CFX  3  January 10, 2007 08:16 
1/7 power law  Eric  Main CFD Forum  0  December 28, 2006 00:48 
Viscosity  power law  HOC  Main CFD Forum  1  January 15, 2003 16:17 