New Functionality in Version 4.1
- A new Spalart-Allmaras Turbulence Model interface is available, which is suited for modeling wings and airfoils.
- Permeability and porosity can be obtained from the Material Library in the Darcy’s Law and Brinkman’s Equation interfaces.
Backward Compatibility vs. Version 3.5a
K-ε Turbulence Model
The new wall functions have the potential to deliver higher accuracy than the formulation used in 3.5a. They might, however, require finer wall resolution. Hence, a 3.5a turbulence model can often benefit from an additional boundary layer mesh or refined boundary layer mesh when imported into 4.1.
K-ω Turbulence Model
The K-ω turbulence model physics interface is not yet implemented in version 4.0a. It is planned for the CFD Module in version 4.2.
Version 4.1 includes automatic translation of models built with the previous k-ω turbulence model. When opened, the full model, including initial values and boundary conditions, is converted to the k-ε turbulence model. Once opened, the model can also be also be changed to the Low-Reynolds k-e Turbulence Model interface. The latter physics interface present an excellent alternative for higher accuracy in models including confined flows.
Pseudo Application Modes
The Pseudo application modes for species transport in version 3.5a allow for the use of the dependent variable for time as a space coordinate in the direction of the flow.
The corresponding physics interfaces are not yet implemented in version 4.1. They are planned for a later version
Meanwhile, you can either create this alternative description manually, by relating time to a position along the length of the reactor using the axial velocity, or you can use a full 2D or 3D model.
Special Basis Functions or Elements
None of the special basis functions or elements for the finite element formulation of flow problems included in version 3.5a are available in version 4.0. However, bubble elements and streamline diffusion are equivalent. Hence, old model that utilized bubble elements can be solved using streamline diffusion instead.
Other special elements that were available in 3.5a will not be re-implemented in version 4. The reason for this is that the stabilized formulation in version 4.0a gives high accuracy to a relatively small computational cost compared to the special elements.
Thin Boundary Layer Pair Boundary Conditions
The Contact Resistance, Transition, and Perfect Magnetic Conductor boundary conditions are not yet available as assembly Pair boundary conditions.
Pair Boundary Conditions
The thin boundary layer approximation approximates the mass flux perpendicular to an interface according to:
where ni denotes the flux of species i, n the normal vector, cs the surface concentration, and cb the bulk concentration of species i.
In the case where cs actually is a concentration in a separate domain, so that the interface between two domains requires a discontinuous concentration but a continuous flux, this condition could be defined in 3.5a using pair boundary conditions.
Figure 1-1: Example of two domains with two separate dependent variables for chemical concentration.
Version 3.5a models using this functionality are not automatically converted to version 4.1. However, you can covert these models manually in version 4.1 by using separate fields for the surface and bulk concentrations.