CFD Module Updates

For users of the CFD Module, COMSOL Multiphysics® version 5.5 includes a new physics interface called Viscoelastic Flow, a new Compressible Euler Equations interface, and nonisothermal flow for large eddy simulations (LES). Learn about these and more CFD Module updates below.

Viscoelastic Flow

Many fluids of interest are macromolecular in nature, including polymeric melts used to make plastics, dough used in the food industry, and biological fluids like synovial fluids in joints. When subjected to deformation, these fluids exhibit both viscous and elastic behavior. Users of the CFD Module now have access to a new physics interface, Viscoelastic Flow, under the Single-Phase Flow branch, for studying flow phenomena including elastic effects. The predefined constitutive models include Oldroyd-B, Giesekus, and FENE-P. You can see this new interface in the Flow of Oldroyd-B Viscoelastic Fluid model.

A model of an abdominal aortic aneurysm visualizing the blood flow with streamlines and total wall stress in red. Blood flow in an abdominal aortic aneurysm. The results show the total wall stress, where a brighter red color indicates a larger stress.

Compressible Euler Equations

In many cases of high-speed flow, the dissipative effects of viscosity, as well as thermal conduction and diffusion, are confined to thin boundary layers along exterior walls and interior surfaces of immersed bodies. Neglecting these effects reduces the computational demands while often yielding good results for lift, wave drag, and over- and under-expanded nozzle conditions. The new Compressible Euler Equations interface solves the Euler equations for isentropic, compressible flow of an ideal gas. The physics interface is applicable to exterior and interior flows at transonic and supersonic speeds as encountered in high-speed aerodynamics, supersonic nozzles and ejectors, and vacuum systems.

A gray rocket model with density variations visualized in blue and white. Density variations around a rocket at supersonic speed, where the light color indicates high density.
The COMSOL Multiphysics UI with the Settings window open for the Compressible Euler Equations interface and a rocket model shown to the right. The Settings window for the Compressible Euler Equations interface showing the equations, numerical flux, and limiter sections.

Phase Transport Mixture Model

Most dispersed multiphase flow applications involve multiple sizes of particles, bubbles, or droplets. The new Phase Transport, Mixture Model multiphysics coupling enables you to include an arbitrary number of dispersed phases in multiphase flow simulations. Predefined multiphysics couplings between single-phase flow and phase transport interfaces have been added for laminar flow and all RANS turbulence models. You can see this new functionality in the Oil–Water Flow Through an Orifice — A Droplet Population Model.

A model of oil droplets passing through an orifice and breaking into smaller droplets. Flow streamlines and volume-averaged droplet size (surface) for turbulent flow of five populations of oil droplets suspended in water. The oil droplets are broken up into smaller droplets by the turbulent stresses as the suspension passes through an orifice.

Nonisothermal Large Eddy Simulation (LES)

The nonisothermal flow functionality has been extended to include LES, enabling detailed studies of buoyancy effects in turbulent flow, including analyses of thermal plumes and convective cooling. Predefined multiphysics couplings have been added for the three current LES models: RBVM, RBVMWV, and Smagorinsky.

Thermal plume rising from a hot cylinder. The animation was created using particle tracing with comet-tail plots.

Continuity and Initial Interface Pair Features

On interior boundaries across which the mesh is discontinuous, such as when two domains slide against each other, the phase-field variables can be made continuous by applying one of two new Pair features: the Continuity and Initial Interface pairs. The Initial Interface pair can, in addition to enforcing continuity of the phase-field variables, be used to smooth an initial discontinuity that may occur as a result of specifying different phases on adjacent domains.

A model of a channel with internal gravity waves shown in blue as well as the mesh. Internal gravity waves generated by a volume force active in the lower half of the channel. The Initial Interface pair is used to make the phase-field variables continuous across an assembly boundary with nonmatching tetrahedral and hexahedral meshes, in the lower and upper half of the channel, respectively.

Inelastic Non-Newtonian Constitutive Relations

Many fluids are non-Newtonian, that is, the relationship between strain and stress is nonlinear. Non-Newtonian behavior can, for example, be observed in aqueous solutions of corn starch, ketchup, blood, and paper pulp. Users of the CFD Module can now simulate two-phase flow of inelastic non-Newtonian fluids using either the Level Set or Phase Field models.

The Settings window in COMSOL Multiphysics for the Two-Phase Flow, Level Set multiphysics coupling with the Domain Selection and Fluid Properties sections open. Settings window for the Two-Phase Flow, Level Set multiphysics coupling node, showing the Power Law option in the inelastic non-Newtonian constitutive relation.

New Tutorial Models

Version 5.5 brings several new and updated tutorial models.

Unsteady 3D Flow Past a Cylinder
A 3D model of a gray cylinder in a channel with the flow visualized as streamlines and a blue-white gradient. Instantaneous streamlines and velocity magnitude for periodic 3D flow around a cylinder in a channel.

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Bimetallic Strip in Airflow
A model of a bending bimetallic strip with airflow around it. Velocity and temperature distribution around a bimetallic strip that bends due to the heating from the warm airflow.

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Two-Phase Flow with Fluid-Structure Interaction
A model of a thin elastic membrane with blue liquid flowing around it. This tutorial is updated with fluid-structure interaction of a thin elastic membrane and a liquid with a free surface.

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Viscous Catenary
A model of a viscous catenary supported at either end and hanging under its own weight. Velocity magnitude and shape of a viscous catenary supported at its endpoints and deforming under gravity, at its initial position and after 2 seconds.

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Two-Phase Flow Modeling of Copper Electrowinning Using Bubbly Flow
A 2D model of a self-stirred electrochemical cell. Velocity profile in a self-stirred electrochemical cell. Convection is induced due to bubble evolution on one of the electrodes.

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