Index

Viscosity function

Ver: 1
 

DESCRIPTION

For the White-Metzner model, entering this menu allows the user to select the shear-rate dependence of the viscosity.
The general form for the viscosity is written as
  visc = F(g) ,   where g is the shear-rate.

Three laws are available for F(g) :
 

* the constant viscosity F(g) = fac
  * the Bird-Carreau law F(g) = facinf + (fac-facinf) * [ 1 + (tnat * g)2](expo-1)/2
  * the Power law F(g) = fac *(tnat * g)expo-1.


For the Bird-Carreau and Power laws, tnat is a natural time, which is not to be confused with the relaxation time of the trelax of the
White-Metzner model.

Before specifying material data, the user must select a viscosity law.

By default, fac = 1.

  OPTIONS
 
-1 
 Upper level menu
1 
 Constant viscosity
2 
 Bird-Carreau law
3 
 Power law
4 
 Modify fac    = 1.0000000E+00
Always available
5 
 Modify tnat   = 1.0000000E+00
Available for non constant viscosity laws
6 
 Modify expo   = 1.0000000E+00
Available for non constant viscosity laws
7 
 Modify facinf = 0.0000000E+00
Available for the Bird-Carreau law
NOTES A low value for the power law index expo leads to strong non-linearities.
A Picard iteration is recommended instead of a full Newton iteration for cases where
expo < 0.7. An evolution scheme can also be used, starting from expo = 1 and decreasing expo.

The units for g and the parameters fac, facinf, tnat and expo are :
 
Parameter
Mass
Length
Time
Temperature
        g
-
-
-1
-
        fac
1
-1
-1
-
        facinf
1
-1
-1
-
        tnat
-
-
   1
-
        expo
-
-
-
-

 SEE ALSO