®
COMSOL Multiphysics

Laminar Flow ModelingLaminar Flow

DemoOutlet

Model Definition Laminar flow in water Fully developed flow at the inlet
 Pressure condition at the outlet
 No-slip conditions at walls
 Symmetry conditions at the twolateral surfaces
 Why?
Typical expansion found in manysystems, e.g. in medtech
Benchmark with flow separation

Inlet

Walls

Symmetry

SymmetryDue to symmetry, we only have to model one eight of the model domain, provided that the flow is steady andthat the inlet flow is perpendicular to the inlet boundary.

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3

4THE FIRST STEPThe Model Wizard
When creating a new model, theModel Wizard assists with selecting: Dimension (3D, 2D, 1D, or 0D)
 Physics interface(s) from the physics list
 Study for the physics interfaces

1. Select Model Wizard.
2. Select space dimension.
3. Select physics interfaces.
4. Select study.

Application Builder andModel Manager
Buttons to switch to theApplication Builder orModel Manager.

RibbonIncludes controls for all steps of the modeling process.

Graphics Window Toolbar

COMSOL Desktop®
Model Builder

Model Builder Window
The model tree, together
with the associatedtoolbar buttons, provides
an overview of the model.
The modeling process canbe controlled fromcontext-sensitive menus.

Graphics WindowSettings Window
Shows the settings for thenode that is selected in
the model tree.

Presents interactive
graphics for geometry,mesh, and results.

Information Window Shows messages, progress, and log.

Definitions Geometry

Model tree shows
sequences ofoperations

Definitions
Geometry
Materials
Physics
Mesh
StudyResults

Materials Physics

Mesh

Study Results

Ribbon tabs for all steps in
the modeling process

Definitions Geometry

Model tree showssequences ofoperations

Definitions
Geometry
Materials
Physics
MeshStudyResults

Materials Physics Mesh Study Results

Home tab with the mostcommon commands in themodeling process

ModelImplementation
First model example:
 Define the model and solve theproblem in a minimum of steps
 Once solved, we will go back andbriefly review the procedure

Definitions:- Load parameters from file
Geometry:- Import sequence
Materials:- Load from Material Library
Physics:- Define inlet, symmetry, and outlet
Mesh:- Select mesh
Study:- Select compute
Results:- Plot streamlines
Overview of procedure for first model example

Demo: Model Wizard
1. Select Model Wizard

2. Select space dimension

3. Select physics interfaces

4. Select study

Demo: Parameters & Geometry

Navigate the course material and choose“backstep_parameters.txt”

Navigate the course material and choose“backstep_geom_sequence.mph”

Demo: Materials

Demo: Laminar Flow - Inlet

Demo: Laminar Flow - Outlet

Demo: Laminar Flow - Symmetry

Demo: Mesh & StudyDemo: Results – Velocity Streamlines

Results
 Flow and pressure fields
 Length of recirculation zone
 Total pressure loss Extending the model:
How is the recirculation zone
affected by the inlet velocity?
When do we need to elongate theoutlet section?
When do we need to use aturbulence model?
How can we create an app?

u0 = 1[cm/s]

ModelImplementation
 Model extension:
Variables for computing
recirculation zone
Parametric sweep of inlet velocity
Mesh convergence study
Create an app

Definitions:- Variable for evaluation
Geometry:- Unchanged
Materials:- Unchanged
Physics:- Unchanged
Mesh:- Unchanged
Study:- Add a parametric sweep
Results:- Plot length of recirculation zone
Overview of procedure for extended model example

Results
 Flow and pressure fields
 Length of recirculation zone Note:Recirculation reaches the outlet-> elongate the outlet section

u0 = 1.5[cm/s]

Results
 Flow and pressure fields
 Length of recirculation zone Next possible step:
Mesh convergence analysis, howdoes the length of the zone changewith mesh size?
Seems to converge around a valueof 1.89 cm

u0 = 1[cm/s]

Exercise
Reproduce backstep modelwith varying inlet velocity

OutletModel Definition Laminar flow in water Fully developed flow at the inlet
 Pressure condition at the outlet
 No-slip conditions at walls
 Symmetry conditions at the twolateral surfaces
 Why?
Typical expansion found in manysystems, e.g. in medtech
Benchmark with flow separation

Inlet

Walls

Symmetry

SymmetryDue to symmetry, we only have to model one eight of the model domain, provided that the flow is steady andthat the inlet flow is perpendicular to the inlet boundary.

ModelImplementation
 First step:
Define the model and solve theproblem for one parameter value
Variable for computing the lengthof the recirculation zone Second step:
Extend the model with a parameter
sweep
Plot recirculation zone as afunction of inlet velocity

Definitions:- Load parameters from file
Geometry:- Import sequence
Materials:- Load from Material Library
Physics:- Define inlet, symmetry, and outlet
Mesh:- Select mesh
Study:- Select compute
Results:- Plot streamlines
Overview of procedure for first model example