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.

2 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. 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.

3 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.

4 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.. 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.

5 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.

6 87 Wall .. 88 Inlet .. 91 Outlet .. 96 Symmetry .. 98 Open Boundary .. 98 Boundary Stress .. 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.

7 117 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 .. 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.

8 130 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.

9 150 Fan and Grille Boundary Conditions .. 152 Screen Boundary Condition .. 155 Mass Sources for Fluid Flow .. 157 Numerical Stability Stabilization Techniques for Fluid Flow .. 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.

10 172 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.