Viscosity#

Viscosity = {model_name} {float_list} [M/Lt]

Description / Usage#

This card is used to specify the viscosity model for the liquid constitutive equation (see Sackinger et al., 1995). Definitions of the input parameters are as follows:

{model_name}

The name of the viscosity model, which can be one of the following: CONSTANT, USER, USER_GEN, or FILL, LEVEL_SET, CONST_PHASE_FUNCTION.

{float_list}.

One or more floating point numbers (<float1> through <floatn>) whose values are determined by the selection for {model_name}. These are identified in the discussion of each model below. Note that not all models employ a {float_list}.

Thus,

CONSTANT <float1>

This option specifies a constant viscosity for a Newtonian fluid. The {float_list} has a single value:

  • <float1> - value of viscosity

USER <float1>… <floatn

This option specifies that the viscosity will be given by a user-defined model; the model must be incorporated into Goma by modifying function “usr_viscosity” in file user_mp.c. The model parameters are entered in the {float_list} as <float1> through <floatn> and passed to the routine as an array.

USER_GEN <float1>… <floatn>

This option specifies that the viscosity will be given by a generalized user-defined model. This user-defined model must be incorporated by modifying the routine “usr_viscosity_gen” in the file user_mp_gen.c. Any number of parameters can be passed (via <float1> through <floatn>) in here.

FILL <float1> <float2>

The {float_list} for this option requires two values. It invokes a FILL dependent viscosity that is set to the value of float1 if the FILL variable is 1 and float2 if the FILL variable is 0.

LEVEL_SET <float1> <float2> <float3>

This model is used to vary the viscosity in the flow region when a level set function is used to track the boundary between two fluids using level set interface tracking. This choice assures a smooth transition in density across the zero level set contour. The {float_list} contains three values for this model, where:

  • <float1> Fluid viscosity in the negative regions of the level set function, μ-

  • <float2> Fluid viscosity in the positive regions of the level set function, μ+

  • <float3> Length scale over which the transition occurs, \(\alpha\) . If this parameter is set to zero, it will default to one-half the Level Set Length Scale value specified elsewhere in the input deck.

Note: a better way to specify the identical viscosity model is to make use of the 2nd Level Set Viscosity card documented also in this manual.

CONST_PHASE_FUNCTION <floatlist> <float1> <float2>

This model is used to vary the viscosity in the flow regime when phase functions are used to track the motion of muliple phases. This choice assures a smooth transition in viscosity across the phase boundaries. The {float_list} contains a variable number of values that depend on the number phase functions being tracked, where:

  • <floatlist> list of float variables equal to the number of phase functions. These are the constant viscosities associated with each phase in order from 1 to number of phase functions.

  • <float1> Length scale over which the transition between one phases viscosity value to theother occurs, \(\alpha\) . If this parameter is set to zero, it will default to one-half the Level Set Length Scale value already specified.

  • <float3> The “null” value for viscosity. This is the value for viscosity which will be assigned to those regions of the flow where all the phase functions are less than or equal to zero.

The user should examine the CONST_PHASE_FUNCTION density model for a detailed description of the relations used to compute viscosity with this model. That model refers to densities but the same equations apply if viscosities are exchanged for densities.

TABLE <integer1> <character_string1> {LINEAR | BILINEAR} [integer2] [FILE = filenm]

Please see discussion at the beginning of the material properties chapter 5 for input description and options. Currently the only valid options for character_string1 is TEMPERATURE and MASS_FRACTION.

Examples#

The following is a sample card that sets the viscosity to USER:

Viscosity = USER 1. 1. 1. 1. 1.

Viscosity = LEVEL_SET 0.083 0.0001 0.1

Technical Discussion#

The viscosity specified by this input card is used with the NEWTONIAN Liquid Constitutive Equation.

References#

Sackinger, P. A., Schunk, P. R. and Rao, R. R. 1995. “A Newton-Raphson Pseudo-Solid Domain Mapping Technique for Free and Moving Boundary Problems: A Finite Element Implementation”, J. Comp. Phys., 125 (1996) 83-103.