The CFD Module User’s Guide - COMSOL Multiphysics

1 CFD ModuleUser s GuideContact InformationVisit the Contact COMSOL page at to submit general inquiries, contact Technical Support, or search for an address and phone number. You can also visit the Worldwide Sales Offices page at for address and contact you need to contact Support, an online request form is located at the COMSOL Access page at Other useful links include: Support Center: Product Download: Product Updates: COMSOL Blog: Discussion Forum: Events: COMSOL Video Gallery: Support Knowledge Base: number: CM021301 CFD Module User s Guide 1998 2018 COMSOLP rotected by patents listed on , and Patents 7,519,518; 7,596,474; 7,623,991; 8,457,932; 8,954,302; 9,098,106; 9,146,652; 9,323,503; 9,372,673; and 9,454,625. Patents Documentation and the Programs described herein are furnished under the COMSOL Software License Agreement ( ) and may be used or copied only under the terms of the license , the COMSOL logo, COMSOL Multiphysics , COMSOL Desktop, COMSOL Server, and LiveLink are either registered trademarks or trademarks of COMSOL AB.

2 All other trademarks are the property of their respective owners, and COMSOL AB and its subsidiaries and products are not affiliated with, endorsed by, sponsored by, or supported by those trademark owners. For a list of such trademark owners, see : COMSOL | 3 ContentsChapter 1: IntroductionAbout the CFD Module 22 Why CFD is Important for Modeling .. 22 How the CFD Module Helps Improve Your Modeling .. 23 Where Do I Access the Documentation and Application Libraries? .. 24 Overview of the User s Guide 28 Chapter 2: Quick Start GuideModeling and Simulations of fluid Flow 32 Modeling Strategy .. 32 Geometric Complexities .. 33 Material Properties .. 33 Defining the Physics Interfaces and Features .. 34 Meshing .. 35 The Choice of Solver and Solver Settings.. 36 The CFD Module Physics Interface Guide .. 37 Common Physics Interface and Feature Settings and Nodes .. 50 The Liquids and Gases Materials Database .. 50 Chapter 3: Single-Phase Flow InterfacesModeling Single-Phase Flow 52 Selecting the Right Physics Interface.

3 52 The Single-Phase Flow Interface Options .. 53 Coupling to Other Physics Interfaces .. 58 The Creeping Flow, Laminar Flow, Turbulent Flow, and Large 4 | CONTENTSEddy Simulation Interfaces 59 The Creeping Flow Interface .. 60 The Laminar Flow Interface .. 61 The Turbulent Flow, Algebraic yPlus Interface .. 65 The Turbulent Flow, L-VEL Interface .. 67 The Turbulent Flow, k- Interface .. 69 The Turbulent Flow, Realizable k- Interface .. 70 The Turbulent Flow, k- Interface .. 71 The Turbulent Flow, SST Interface .. 73 The Turbulent Flow, Low Re k- Interface .. 74 The Turbulent Flow, Spalart-Allmaras Interface .. 76 The Turbulent Flow, v2-f Interface .. 78 The LES RBVM Interface .. 79 The LES RBVMWV Interface .. 80 The LES Smagorinsky Interface .. 81 fluid Properties .. 83 Volume Force .. 87 Initial Values .. 87 Wall .. 88 Inlet .. 91 Outlet .. 96 Symmetry .. 98 Open Boundary .. 98 Boundary Stress.

4 99 Screen .. 101 Vacuum Pump .. 102 Periodic Flow Condition .. 104 Fan .. 105 Interior Fan .. 107 Interior Wall .. 109 Grille .. 111 Flow Continuity .. 112 Pressure Point Constraint .. 112 Point Mass Source .. 113 Line Mass Source .. 113 Generate New Turbulence Model Interface.. 114 Gravity .. 116 CONTENTS | 5 The Rotating Machinery, Laminar and Turbulent Flow Interfaces 117 Moving Mesh .. 117 The Rotating Machinery, Laminar Flow Interface .. 118 The Rotating Machinery, Turbulent Flow, Algebraic yPlus Interface .. 120 The Rotating Machinery, Turbulent Flow, L-VEL Interface .. 121 The Rotating Machinery, Turbulent Flow, k- Interface .. 122 Domain, Boundary, Point, and Pair Nodes for the Rotating Machinery Interfaces.

5 123 Stationary Free Surface .. 124 Contact Angle .. 126 Theory for the Single-Phase Flow Interfaces 127 General Single-Phase Flow Theory .. 128 Compressible Flow .. 130 Weakly Compressible Flow .. 130 The Mach Number Limit .. 131 Incompressible Flow .. 132 The Reynolds Number.. 132 Non-Newtonian Flow .. 133 Gravity .. 135 Theory for the Wall Boundary Condition .. 138 Prescribing Inlet and Outlet Conditions .. 141 Mass Flow .. 143 Fully Developed Flow (Inlet) .. 144 Fully Developed Flow (Outlet).. 145No Viscous Stress .. 146 Normal Stress Boundary Condition .. 147 Pressure Boundary Condition .. 147 Vacuum Pump Boundary Condition .. 149 Fan Defined on an Interior Boundary .. 150 Fan and Grille Boundary Conditions .. 152 Screen Boundary Condition .. 155 Mass Sources for fluid Flow .. 157 Numerical Stability Stabilization Techniques for fluid Flow.

6 159 Solvers for Laminar Flow .. 161 Pseudo Time Stepping for Laminar Flow Models .. 163 Discontinuous Galerkin Formulation .. 1656 | CONTENTSP article Tracing in fluid Flow .. 165 References for the Single-Phase Flow, Laminar Flow Interfaces .. 166 Theory for the Turbulent Flow Interfaces 168 Turbulence Modeling .. 168 The Algebraic yPlus Turbulence Model .. 172 The L-VEL Turbulence Model .. 176 The k- Turbulence Model .. 178 The Realizable k- Turbulence Model .. 185 The k- Turbulence Model .. 186 The SST Turbulence Model .. 191 The Low Reynolds Number k- Turbulence Model .. 194 The Spalart-Allmaras Turbulence Model .. 198 The v2-f Turbulence Model .. 201 Inlet Values for the Turbulence Length Scale and Turbulent Intensity .. 206 Theory for Buoyancy-Induced Turbulence .. 207 Theory for the Pressure, No Viscous Stress Boundary Condition .. 208 Initial Values for Generate New Turbulence Model Interfaces.

7 209 Solvers for Turbulent Flow .. 211 Pseudo Time Stepping for Turbulent Flow Models .. 212 References for the Single-Phase Flow, Turbulent Flow Interfaces .. 212 Theory for the Large Eddy Simulation Interfaces 215 References for LES .. 217 Theory for the Rotating Machinery Interfaces 218 Frozen Rotor .. 219 Setting Up a Rotating Machinery Model .. 221 References .. 222 Chapter 4: Heat Transfer and Nonisothermal Flow InterfacesModeling Heat Transfer in the CFD Module 224 Selecting the Right Physics Interface.. 224 CONTENTS | 7 Coupling to Other Physics Interfaces .. 226 The Nonisothermal Flow and Conjugate Heat Transfer, Laminar Flow and Turbulent Flow Interfaces 228 Advantages of Using the Multiphysics Interfaces .. 228 The Nonisothermal Flow, Laminar Flow and Turbulent Flow Interfaces .. 229 The Conjugate Heat Transfer, Laminar Flow and Turbulent Flow Interfaces .. 230 Settings for Physics Interfaces and Coupling Features.

8 231 Coupling Features .. 231 Physics Interface Features .. 232 Nonisothermal Flow .. 233 Flow Coupling .. 237 Marangoni Effect .. 239 Theory for the Nonisothermal Flow and Conjugate Heat Transfer Interfaces 241 The Nonisothermal Flow and Conjugate Heat Transfer Equations .. 241 Turbulent Nonisothermal Flow Theory .. 243 The Boussinesq Approximation .. 248 Theory for the Nonisothermal Screen Boundary Condition.. 249 Theory for the Interior Fan Boundary Condition .. 250 References for the Nonisothermal Flow and Conjugate Heat Transfer Interfaces .. 250 Chapter 5: High Mach Number Flow InterfacesThe High Mach Number Flow Interfaces 254 The High Mach Number Flow, Laminar Interface .. 255 The High Mach Number Flow, k- Interface.. 257 The High Mach Number Flow, Spalart-Allmaras Interface .. 259 Domain, Boundary, Edge, Point, and Pair Nodes for the High Mach Number Flow Laminar and Turbulent Interfaces.

9 260 Initial Values .. 262 fluid .. 2628 | CONTENTSI nlet .. 265 Outlet .. 266 Symmetry .. 267 Theory for the High Mach Number Flow Interfaces 269 Compressible Flow for All Mach Numbers .. 269 Sutherland s Law .. 271 Consistent Inlet and Outlet Conditions .. 272 Pseudo Time Stepping for High Mach Number Flow Models .. 276 References for the High Mach Number Flow Interfaces .. 277 Chapter 6: Multiphase Flow InterfacesModeling Multiphase Flow 280 Selecting the Right Physics Interface.. 280 The Multiphase Flow Interface Options .. 281 The Relationship Between the Physics Interfaces .. 281 Coupling to Other Physics Interfaces .. 288 The Two-Phase Flow, Level Set and Phase Field Interfaces 290 The Laminar Two-Phase Flow, Level Set Interface .. 290 The Turbulent Two-Phase Flow, Level Set Interfaces .. 291 The Two-Phase Flow, Level Set Coupling Feature .. 293 The Wetted Wall Coupling Feature.

10 295 The Interior Wetted Wall Coupling Feature .. 298 The Laminar Two-Phase Flow, Phase Field Interface .. 300 The Turbulent Two-Phase Flow, Phase Field Interfaces .. 301 The Two-Phase Flow, Phase Field Coupling Feature.. 302 Domain, Boundary, Point, and Pair Nodes for the Laminar and Turbulent Flow, Two-Phase, Level Set and Phase Field Interfaces .. 305 The Three-Phase Flow, Phase Field Interface 306 The Laminar Three-Phase Flow, Phase Field Interface .. 306 The Three-Phase Flow, Phase Field Coupling Feature .. 307 Domain, Boundary, Point, and Pair Nodes for the Laminar Three-Phase Flow, Phase Field Interface .. 309 CONTENTS | 9 The Bubbly Flow Interfaces 311 The Laminar Bubbly Flow Interface .. 311 The Bubbly Flow, Algebraic yPlus Interface .. 314 The Bubbly Flow, L-VEL Interface .. 315 The Bubbly Flow, k- Interface.. 317 The Bubbly Flow, Realizable k- Interface.. 319 The Bubbly Flow, k- Interface.