CFD Module

New Functionality in Version 5.2a

Weakly Compressible Flow Option

There is a new compressibility option in the fluid flow interfaces. The new Weakly compressible flow option is suitable for nonisothermal flow, when density variations with respect to pressure are negligible. This is the case for the majority of flows at Mach numbers less than 0.3. The advantage of using this option instead of the Compressible flow (Ma < 0.3) option is that pressure waves, traveling at the speed of sound, need not be resolved in time-dependent simulations.

Gravity Property and Feature

A gravity property is now available for the Single-Phase Flow and Non-Isothermal Flow branches (except Rotating Machinery) and can be selected at the interface level. When the gravity property is activated, a volume force due to gravity is added on all domains where the fluid flow interface is active, and a Gravity feature appears in the model tree. The gravity property adds an option to compensate for the hydrostatic pressure where a pressure-type boundary condition, such as an Outlet, Open Boundary, or Boundary Stress condition, is specified. This compensation is exact for incompressible flow, and for the other two compressibility options, it gives a good approximation of the pressure profile on the outlet. There is also an option to use the reduced pressure — that is, to automatically include the hydrostatic pressure in the definition of the dependent variable for pressure.

Boussinesq Approximation in Nonisothermal Flow

When incompressible nonisothermal flow is simulated using a material for which the coefficient of thermal expansion is defined, a buoyancy force with a linear temperature dependence is added, while all fluid properties (such as density, viscosity, and thermal conductivity) remain constant. This is generally referred to as Boussinesq approximation, and it is a popular modeling approach in nonisothermal flow applications. An alternative to specifying the linearization point using a built-in material is to define the reference density and coefficient of thermal expansion explicitly in the Multiphysics node.

Swirl Flow for the Fan Feature

The flow direction now includes a swirl option for fans applied on inlets. The swirl on the downstream side of the fan is determined by setting the rotation rate and a swirl coefficient defined as the ratio of the angular velocity of the flow to that of the blades.

New Two-Phase Flow, Level Set and Two-Phase Flow, Phase Field Multiphysics Interfaces

New Two-Phase Flow, Level Set and Two-Phase Flow, Phase Field multiphysics interfaces, replacing the previous versions, are available in the Model Wizard. By selecting a Two-Phase Flow interface under the Multiphase Flow branch, a laminar or turbulent Single-Phase Flow interface and a Level Set or Phase Field interface are added to the Model Builder. In addition, a multiphysics coupling feature, Two-Phase Flow, Level Set or Two-Phase Flow, Phase Field, is added under the Multiphysics node. The Two-Phase Flow multiphysics coupling feature has predefined controls and couplings between the separate interfaces. In addition, a Wetted Wall boundary condition feature can be added in the Multiphysics node. Opening an application from an earlier version, the previous Two-Phase Flow interfaces are used.

Updated Crosswind Stabilization

The consistent crosswind stabilization has been improved.