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Computational Fluid Dynamics

With SolidWorks

Laminar Flow in a Pipe

Laminar flow in a pipe is determined by the Reynolds number. The Reynolds number has to

be less than 2000 for laminar flow conditions to exits.

where is the density of the fluid

v is the velocity of the fluid

d is the pipe diameter

is the dynamic viscosity of the pipe.

In this study SolidWorks will be used to investigate the flow of water in a straight pipe. The

pipe has an internal diameter of 25 mm and an external diameter of 28mm. The surface

roughness of the pipe is 8 m. The fluid properties of water are:

Table 1 Fluid properties of water

Property Symbol Value Units

Density 1000 kg/m

Dynamic Viscosity 1.002x10-

The Reynolds number for this analysis is to be 1000. This would be achieved with a velocity

of 0.0401m/s.

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SolidWorks

The first stage of the analysis is to define the geometry in SolidWorks.

Create a New Part.

Choose Extrude Boss/Base from the Features menu.

On the Right Plane draw two circles with their centres at the origin. Dimension the

circles with one at 25 mm diameter and the other at 28mm. Exit the sketch.

Extrude by 300mm

Right Click on Boss-Extrude1 and select Change Transparency from the resulting

menu.

Save the part

To start a fluid flow analysis the part must be saved. The pipe has been made transparent so

that the internal portion can be seen. This helps with selection and result viewing. The flow

simulation can now begin.

Tools Add-Ins...

Tick the SolidWorks Flow Simulation 2011Active Add-ins box

[OK]

A Flow Simulation tab should appear above the graphics window. The problem domain

needs to be defined. For a analysis of internal flow SolidWorks needs to have surfaces to

define where the fluid flows from and where it flows to. This is achieved by creating Lids

at all entry and exit positions. In this case a lid is required at either end of the pipe.

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Select the Flow Simulation Tab

Select the Lids icon

Select the two flat surfaces at either end of the pipe

Accept the selection

The screen should now appear as inFigure 1.

Figure 1 Pipe with lids

The details of the problem can now be defined using the flow Wizard.

Select the Wizard icon

The project configuration dialogue box appears.

Change the Configuration name: to Laminar-Pipe

In the Comments: box add Re=1000

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[Next>]

As the pipe dimensions are in millimetres:

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Select NMM (mm-g-s) as the Unit system:

[Next>]

As the flow is internal and the reference axis is X the default settings can be accepted.

[Next>]

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The fluid used for the simulation needs to be defined. SolidWorks provides a database of

properties of fluids and gases.

Expand the [+] Liquids entry.

Scroll down the list to the bottom

Select Water

[Add]

The surface roughness of the pipe is added at this stage.

Change Roughness to 8 micrometers

[Next>]

This results in the Initial Conditions dialogue box. The default initial conditions are fine for

this analysis.

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[Next>]

[Finish]

The slider for the results resolution increases the fineness of the grid. For this initial analysis

the default analysis will be chosen. Note that increasing the results resolution will lengthen

the analysis considerably.

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In the property manager an additional tab has appeared. This is the Flow Simulation Analysis

tree.

The next stage of the analysis is to apply the boundary conditions. The inlet flow conditions

can be set to fluid velocity, mass flow rate or

Right click Boundary Condition on the flow simulation tree

Insert boundary conditions...

Highlight the Faces to apply boundary conditions box and select the inner face of the

lid at the domain origin.

Select Inlet Velocity from the

Type list

In the Flow Parameters enter the

velocity (40.1mm/s) in the V box

Select OK

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Note that there is an option for fully developed flow conditions to exist in the pipe. In this

case this has not been chosen and the results will be examined to check if the pipe is long

enough for the flow to develop fully.

At the other end of the pipe the fluid will exit at a static pressure. The static pressure will be

ambient pressure.

Right click Boundary Condition on the flow simulation tree

Insert boundary conditions...

Highlight the Faces to apply boundary conditions box and

select the inner face of the lid at the opposite end of the

pipe from the origin.

Select Pressure Openings

In the Type options select Static Pressure

The default values of pressure and temperature are

shown for the static pressure. These are the values to

be used for this analysis.

Select OK

A goal now has to be set. The goal is the value of one of the unknowns being calculated

which is to be used to determine when the solution has converged. In this case the solution

will cease when the average static pressure at the outlet has converged.

Right Click Goals in the flow analysis tree

Select Insert Global Goals...

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Tick the Av (average) box on the Static P(ressure) row.

Select OK

The analysis set-up is now complete. The analysis can now be run.

Select the Run icon

Select [Run]

A solver dialogue box now appears. It shows information as to how the analysis is

progressing. A message will appear at the bottom of the dialogue box when the solver has

finished. The results can now be reviewed. SolidWorks offers a whole range of different

options for view fluid flow results.

Right click Cut Plots

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Insert...

Click on the Contours icon (to deselect it)

Click on the Isolines icon

Change Pressure to Velocity

Change the number of levels to 30

Select OK

This shows a series of lines of constant velocity. It can be seen from the plot that the velocity

profiles changes from the inlet to the outlet. This is because the flow has not fully developed

all the way along the pipe. It can be seen that towards the outlet end of the pipe the contours

seem to be indicating that fully developed flow may have been achieved. It can be seen from

the scale that the fluid velocity is higher along the centre of the pipe and reduces towards the

wall of the pipe. This would be expected as the velocity at the wall would normally be

considered to be zero.

The profile of the velocity at any cross section can be viewed.

Right Click Cut Plot 1

Hide

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Right Click Cut Plots

Insert...

Set the view so that the screen shows the front plane.

Select the Normal to screen, Vertically icon

A line appears on the screen and a box (Vertical Position) with a value of 500.

Changing this value moves the line on the screen to the left or the right.

Set the value so that the line in near the exit of the pipe

In the Contour box change Pressure to Velocity

Select the 3D profile icon

Select OK

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This shows the velocity profile at the section.