Initial and Conditional Data window shown in Figure 15 can be started by following the menu sequence Data>Initial data . Data included in this window refers to all the information required for defining the initial status of the problem (t=0).
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A description of every option available in the Initial and Conditional Data window is given next.
Pressure Field : Initial (t=0) and reference dynamic pressure field. May be a constant or a function. See Function Syntax section for further information.
Remarks:
If any Pressure Field condition has been assigned to any entity within this material, this field will be used as a base to calculate the boundary condition. If the Fix Initial field has been marked, the pressure will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field has been marked, the pressure will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the pressure this way.
It is possible to assign different initial conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
Velocity X/Y/Z Field : Initial (t=0) and reference OX/OY/OZ velocity field. May be a constant or a function. See Function Syntax section for further information.
Remarks:
If any Velocity Field condition has been assigned to any entity within this material, this field will be used as base to calculate the boundary condition. If the corresponding Fix Initial X/Y/Z field has been marked, the OX/OY/OZ component of the velocity will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field X/Y/Z field has been marked, the OX/OY/OZ component of the velocity will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the velocity this way.
It is possible to assign different initial conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
EddyKEn Field : Initial (t=0) field of the eddy kinetic energy (kinetic energy of the fluctuating component of the velocity). In some cases may be useful to define this field as a function of the so called Turbulence Intensity Level or TIL, defined by the relation k = TIL·V2 , being k the eddy kinetic energy and V a characteristic velocity of the problem. May be a constant or a function. See section Function Syntax for further information.
In external flows over airfoils the turbulence level is typically TIL = 0.003 (0.3%), however in atmospheric boundary layer flows the level can be two orders of magnitude higher (TIL = 0.30). In internal flows a turbulence level of TIL = 0.05 to 0.10 (5 to 10%) is usually appropriate.
Remarks:
If any Fix Turbulence condition has been assigned to any entity within this material, this field will be used as a base to calculate the boundary condition. Turbulence will then be fixed to the initial value (evaluated in t = 0) of the function inserted here.
It is possible to assign different initial conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
EddyKEn Field entry will only be useful for those turbulence models based on Reynolds extended analogy (see Turbulence Modelling section for further information).
EddyLength Field : Initial (t=0) and reference field of the turbulence length scale (L) field, defined by the relation μT = ρ·k½ ·L, being k the eddy kinetic energy, μT the eddy viscosity and ρ the density field. May be a constant or a function. See Function Syntax section for further information.
For external flows remote from boundary layers, a value determined by the assumption that the ratio of turbulent and molecular viscosity μT /μ is between 1 and 10 is a reasonable guess. Taking into account the above definitions:
L=μ/(ρ·TIL1/2 ·V)·(μ/μT )*
where * indicates the prescribed parameter.
For internal flows, a constant value of length scale, derived from a characteristic geometrical feature can be used (e.g. 1 to 10% of the hydraulic diameter for internal flows).
Other possibility is to calculate L from the recommended values for the initial variables of the turbulence model to be used, as shown next (note that next relations are not definitions):
ε=0.009·k2 /(4·μT )
ω>C·V/LD with 10 ≤ C ≤ 100
kτ=0.09/μT
where V and LD are the characteristics velocity and length of the problem.
Remarks:
If any Fix Turbulence condition has been assigned to any entity within this material, this field will be used as a base to calculate the boundaries condition for the turbulence. Turbulence will be then fixed to the initial value (evaluated in t = 0) of the function inserted here.
It is possible to assign different initial conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
EddyKEn Field entry will only be useful for those turbulence models based on Reynolds extended analogy (see Turbulence Modelling section for further information).
Pressure FuncCond : Conditional function used for defining Conditional Pressure boundary conditions. Conditional Pressure boundary conditions will only be applied if the Pressure FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the Pressure FuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
Velocity X/Y/Z FuncCond : Conditional function used for defining Conditional Velocity boundary conditions. Conditional Velocity boundary conditions will only be applied if the Velocity X/Y/Z FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the Velocity X/Y/Z FuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
Temperature Field : Initial (t=0) and reference temperature field. May be a constant or a function. See Function Syntax section for further information.
Remarks:
If any Temperature Field condition has been assigned to any entity within this material, this field will be used as a base to calculate boundary conditions. If the corresponding Fix Initial field has been marked, the temperature will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field has been marked, the temperature will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the temperature this way.
Temperature FuncCond : Conditional function used for defining Conditional Temperature boundary conditions. Conditional Temperature boundary conditions will only be applied if the Temperature FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the Temperature FuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
Concentration Field : Initial (t=0) and reference concentration field. May be a constant or a function (see Function Syntax section for further information). There is one Concentration Field entry for every Species. Available species can be selected by clicking on its name in the listbox at the left of the window.
Remarks:
If any Concentration Field condition has been assigned to any entity within this material, this field will be used as a base to calculate boundary conditions. If the corresponding Fix Initial field has been marked, the concentration of the species will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field has been marked, the concentration of the species will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the concentration of the species this way.
SpeciesFuncCond : Conditional function used for defining Conditional Concentration boundary conditions. Conditional Concentration boundary conditions will only be applied if the Species FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the SpeciesFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step. There is one Species FuncCond field for every Species. Available species can be selected by clicking on its name in the listbox at the left of the window.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
Variable Field : Initial (t=0) and reference variable field. May be a constant or a function (see Function Syntax section for further information). There is one Variable Field entry for every variable. Available variables can be selected by clicking on its name in the listbox at the left of the window.
Remarks:
If any Variable Field condition has been assigned to any entity, this field will be used as a base to calculate boundary conditions. If the corresponding Fix Initial field has been marked, the value of the variable will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field has been marked, the value of the variable will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the variables this way.
Variable FuncCond : Conditional function used for defining Conditional Variable boundary conditions. Conditional Variable boundary conditions will only be applied if the Variable FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the Variable FuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step. There is one Variable FuncCond field for every variable. Available variables can be selected by clicking on its name in the listbox at the left of the window.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).
OddLevelSet Field : Initial (t=0) and reference field for level set function. May be a constant or a function (see Function Syntax section for further information). If the checkbutton is selected, the level set distance function is created from the function entered in OddLevelSet Field . For this purpose, those nodes with positive values conected to nodes with non-positive values are considered to be on the interface between both phases. Primary phase is initiated in those nodes with positive values.
Remarks:
If any ODDLS Field condition has been assigned to any entity, this field will be used as a base to calculate boundary conditions. If the corresponding Fix Initial field has been marked, the value of the variable will be fixed to the initial value (evaluated in t = 0) of the function inserted here.
If the corresponding Fix Field has been marked, the value of the variable will be fixed to the value (for every time step) of the function inserted here. It is possible to define transient boundary conditions for the variables this way.
OddLevelSet FuncCond : Conditional function used for defining Conditional ODDLS boundary conditions. Conditional ODDLS boundary conditions will only be applied if the OddLevelSet FuncCond field value (resulting of the evaluation of the given function) is greater than 0. If the evaluation of the OddLevelSet FuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step. There is one OddLevelSet FuncCond field for every variable. Available variables can be selected by clicking on its name in the listbox at the left of the window.
Remarks:
It is possible to assign different ‘FuncCond’ conditions for every material by using ‘if’ clauses and ‘mat’ function (see Function Syntax section for further information).