Comsol - CFD Modeling Software for Single-Phase and Multiphase Flows
From Fluid Flow & Heat Transfer Modules
Define and solve models for studying systems containing fluid flow and fluid flow coupled to other physical phenomena with the CFD Module, an add-on product to the COMSOL Multiphysics® simulation platform.
The CFD Module provides tools for modeling the cor...
The CFD Module provides tools for modeling the cornerstones of fluid flow analyses, including:
- Internal and external flows
- Incompressible and compressible flows
- Laminar and turbulent flows
- Single-phase and multiphase flows
- Free and porous media flows
The multiphysics capabilities are virtually unlimited within the module and in combination with other add-on modules to COMSOL Multiphysics®. The CFD Module provides you with the tools to model nonisothermal flow with conjugate heat transfer, reacting flow, fluid–structure interaction (FSI), and electrohydrodynamics (EHD). Additional multiphysics couplings can be added together with other modules from the COMSOL product suite, such as combining fluid flow with large structural deformations in FSI. The simulation environment looks the same regardless of what you are modeling.
Laminar and Creeping Flow
Model transient and steady laminar flow with the Navier–Stokes equations or creeping flow with the Stokes equations.
In addition to modeling fluids with constant density and viscosity, you can study fluids where the viscosity and density depend on the temperature, local composition, electric field, or any other modeled field or variable. In general, density, viscosity, and momentum sources can be arbitrary functions of any dependent variable, as well as derivatives of dependent variables.
For non-Newtonian fluids, you can use the generic yet predefined rheology models for viscosity, such as Power Law, Carreau, Bingham, Herschel–Bulkley or Casson for easy model setup.
You can also model laminar flow in moving structures, for example opening and closing valves or rotating impellers.
Turbulent Flow
A comprehensive set of Reynolds-averaged Navier–Stokes (RANS) turbulence models are available in predefined flow interfaces in the CFD Module. These models allow you to simulate a wide range of steady and transient turbulent flows. You can also change or extend the model equations directly in the user interface to create turbulence models that are not yet included.
RANS Turbulence Models
Two-Equation Models
- k-ε
- Realizable k-ε
- k-ω
- SST
- Low-Re k-ε
Additional Transport Equation Models
- Spalart–Allmaras
- v2-f
Algebraic Turbulence Models
- Algebraic yPlus
- L-VEL
Wall Treatment
Wall Functions
Robust and applicable for coarse meshes, with limited accuracy.
Low-Reynolds-Number Treatment
Resolves the flow all the way down to the walls. Accurate but requires a fine mesh.
Automatic Wall Treatment
Inherits the robustness provided by wall functions, with an accuracy of low-Re treatment in well-resolved regions.
Large Eddy Simulation (LES)
Large eddy simulation (LES) is used for resolving larger three-dimensional unsteady turbulent eddies, whereas the effects of the smaller eddies are approximately represented. When combined with boundary layer meshing, this technique gives an accurate description of a transient flow field as well as accurate fluxes and forces at the boundaries. The available LES models are residual-based variational multiscale (RBVM), residual-based variational multiscale with viscosity (RBVMWV), and Smagorinsky.
In separated multiphase flow systems, you can use surface tracking methods to model and simulate the behavior of bubbles and droplets, as well as free surfaces. For such cases, by using the level set and phase field methods, the shape of the phase boundary can be described in detail, including surface tension effects and topology changes.
When bubbles, droplets, or particles are small compared to the computational domain and there is a large number of them, you can use dispersed multiphase flow models. These models keep track of the mass or volume fractions of the different phases and the influence that the dispersed bubbles, droplets, or particles have on the transfer of momentum in the fluid in an averaged sense. The flow models available are: the bubbly flow, mixture, Euler–Euler, and phase transport mixture models.
The CFD Module makes it simple to simulate fluid flow in porous media using three different porous media flow models. The Darcy's Law model is a robust and computationally inexpensive description of flows in porous structures. It is also available for multiphase flow. The Brinkman Equations model is an extension of Darcy's law that accounts for the dissipation of kinetic energy by viscous shear, and can include inertial effects. Relevant for highly open structures with high porosity, this model is more general than Darcy's law, but also more computationally expensive.
The Free and Porous Media Flow model couples flow in porous domains with laminar or turbulent flow in free domains. The model formulates the Brinkman equations for the porous domain and the Navier–Stokes equations for the free domains.
For more details on specific features and functionality, see the Porous Media Flow Module or Subsurface Flow Module.
Model transonic and supersonic flows of compressible fluids in both laminar and turbulent regimes. The laminar flow model is typically used for low-pressure systems and it automatically defines the equations for momentum, mass, and energy balances for ideal gases. High Mach number flow is also available for the k-ε and Spalart–Allmaras turbulence models.
In both cases, when solving these models, automatic mesh refinement can be used to resolve the shock pattern by refining the mesh in regions with very high velocity and pressure gradients.
Rotating machines, such as mixers and pumps, are common in processes and equipment where fluid flow occurs. The CFD Module provides rotating machinery interfaces that formulate the fluid flow equations in rotating frames, available for both laminar and turbulent flow. You can solve problems using either a full time-dependent description of the rotating system or an averaged approach based on the frozen rotor approximation. The frozen rotor approach is computationally inexpensive and can be used to estimate averaged velocities, pressure changes, mixing levels, averaged temperature and concentration distributions, and more.
Generally speaking, the CFD Module can also solve fluid flow problems on any moving frame, not just on rotating frames, for example opening and closing valves. You can use moving frames to solve a problem where a structure slides in relation to another structure with fluid flow in between, which is easy to set up and solve by employing a moving mesh.
To describe flows in thin domains, such as thin oil films between moving mechanical parts (tribology) or fractured structures, the CFD Module provides the Thin Film Flow interfaces. This formulation is typically used for modeling lubrication, elastohydrodynamics, or effects of fluid damping between moving parts due to the presence of gases or liquids (for example, in MEMS).
The shallow water equations allow you to model flow below a free surface under the condition that the horizontal length scale is much greater than the vertical length scale. The shallow water equations are obtained by depth-averaging the Navier–Stokes equations. The dependent variables are the water depth and momentum flux. The equations can be used to model effects of tsunamis and flooding.
Creating Real-World Multiphysics Models
Modeling multiple physics phenomena in COMSOL Multiphysics® is no different than a single-physics problem.
Laminar Nonisothermal Flow
Temperature-dependent fluid properties and buoyancy forces; continuous temperature and heat flux across the solid–fluid boundary.
A detailed view of the smoke produced by an incense stick at three different times.
Turbulent Nonisothermal Flow
Low-Re formulation or thermal wall functions for the conjugate heat transfer at solid–fluid boundaries with RANS or LES.
FSI: One-Way Studies
Fluid–structure interaction where the flow creates a load on a structure but the deformations are so small that they do not impact the flow.
FSI: Fully Coupled1
Fluid–structure interaction where the flow creates loads on a structure, and the deformations are large and affect the flow.
General Reacting Flow
Multicomponent transport and reactions in diluted and concentrated mixtures, using the mixture-averaged model or Fick's law.
Advanced Reacting Flow2
The full Maxwell–Stefan multicomponent transport equations for laminar flows.
Mixers3
Multiphase flow and free surfaces for rotating machinery, as well as a Part Library for impellers and vessels.
Particle Tracing4
Euler–Lagrange multiphase flow models, where particles or droplets are modeled as discrete entities.
Pipe Flow and CFD5
Pipes and channels connected to 2D/3D fluid domains with nonisothermal flows, for both laminar and turbulent flows.
General Functionality Adapted for Solving CFD Problems
The Fluid Flow Interfaces
In order to model laminar, turbulent, multiphase, compressible, high Mach number, and thin film flows, as well as the shallow water equations, the CFD Module provides a large number of fluid flow interfaces tailored for different regimes of these flows. Each fluid flow interface defines sets of domain equations, boundary conditions, initial conditions, predefined meshes, predefined studies with solver settings for steady and transient analyses, as well as predefined plots and derived values.
Materials
The CFD Module includes a material library with the most common gases and liquids. In combination with the Chemical Reaction Engineering Module or the Liquid & Gas Properties Module, you can also access generic descriptions for thermodynamic properties of fluids (such as viscosity, density, diffusivity, thermal conductivity, heat of formation, and phase transformation).
Discretization
The fluid flow interfaces use Galerkin/least-square and Petrov–Galerkin methods to discretize the flow equations and generate the numerical model in space (2D, 2D axisymmetry, and 3D). The test functions are designed to stabilize the hyperbolic terms and the pressure term in the transport equations. Shock-capturing techniques further reduce spurious oscillations. Additionally, discontinuous Galerkin formulations are used to conserve momentum, mass, and energy over internal and external boundaries.
Evaluating and Visualizing Results
The fluid flow interfaces generate a number of default plots to analyze the velocity and pressure fields. Streamline plots are available to visualize flow and flow direction. Surface and volume plots can be used to show pressure and the velocity vector's magnitude. There is also an extensive list of derived values and variables that can be easily accessed to extract analytical results, for example the drag coefficient.
Geometry
Generate flow domains, such as a bounding box, around imported CAD geometries. Additionally, tools are available to automatically or manually remove details that may not be relevant for fluid flow. With the CAD Import Module, you are able to import most CAD file formats and perform repair and defeaturing operations. The built-in geometry tools for CAD are also able to create complex geometries and domains.
Meshing
The physics-controlled mesh functionality in the CFD Module takes the boundary conditions in the fluid flow problem into consideration when generating the mesh sequence. A boundary layer mesh is automatically generated in order to resolve the gradients in velocity that usually arise at the surfaces where wall conditions are applied.
Solvers
The flow equations are usually highly nonlinear. To solve the numerical model equations, the automatic solver settings select a suitable damped Newton method. For large problems, the linear iterations in the Newton method are accelerated by state-of-the-art algebraic multigrid or geometric multigrid methods specifically designed for transport problems.
For transient problems, time-stepping techniques with automatic time stepping and automatic polynomial orders are used to resolve the velocity and pressure fields with the highest possible accuracy, in combination with the aforementioned nonlinear solvers.
Simulation Applications
You can build user interfaces on top of any existing model using the Application Builder, which is included in COMSOL Multiphysics®. This tool enables you to create applications for very specific purposes with well-defined inputs and outputs. Applications can be used for many different purposes: automate difficult and repetitive tasks, create and update reports, provide user-friendly interfaces for nonexperts, increase access to models within your organization, and gain a competitive edge with your customers.
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