Sign-up for free online course on ANSYS simulations!Step 6: Analyze Results
Plot Velocity Vectors
Let's plot the velocity vectors obtained from the FLUENT solution.
Display > Vectors
Set the Scale to 14 and Skip to 4. Click Display.
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{panel} [Problem Specification|FLUENT - Steady Flow Past a Cylinder - Problem Specification]\\ [1. Create Geometry in GAMBIT|FLUENT - Steady Flow Past a Cylinder - Step 1]\\ [2. Mesh Geometry in GAMBIT|FLUENT - Steady Flow Past a Cylinder - Step 2]\\ [3. Specify Boundary Types in GAMBIT|FLUENT - Steady Flow Past a Cylinder - Step 3]\\ [4. Set Up Problem in FLUENT|FLUENT - Steady Flow Past a Cylinder - Step 4]\\ [5. Solve|FLUENT - Steady Flow Past a Cylinder - Step 5]\\ {color:#ff0000}{*}6. Analyze Results{*}{color}\\ [7. Refine Mesh|FLUENT - Steady Flow Past a Cylinder - Step 7]\\ [Problem 1|FLUENT - Steady Flow Past a Cylinder - Problem 1]\\ [Problem 2|FLUENT - Steady Flow Past a Cylinder - Problem 2] {panel} h2. Step 6: Analyze Results h4. Plot Velocity Vectors Let's plot the velocity vectors obtained from the FLUENT solution. *Display > Vectors* Set the {color:#660099}{*}{_}Scale{_}{*}{color} to 14 and {color:#660099}{*}{_}Skip{_}{*}{color} to 4. Click {color:#660099}{*}{_}Display{_}{*}{color}. \\ [!step6_velocity_vectorsm.jpg!|^step6_velocity_vector.jpg] {newwindow:Higher Resolution Image}https://confluence.cornell.edu/download/attachments/104400192/step6_velocity_vector.jpg?version=1{newwindow} |
From
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this
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figure,
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we
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see
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that
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there
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is
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a
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region
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of
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low
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velocity
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and
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recirculation
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at
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the
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back
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of
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cylinder.
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Pressure Coefficient
Pressure coefficient is a dimensionless parameter defined by the equation 
where p is the static pressure, p ref is the reference pressure, and q ref is the reference dynamic pressure defined by
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} {info} h4. Pressure Coefficient Pressure coefficient is a dimensionless parameter defined by the equation !step6_cp_equation.gif! where _p_ is the static pressure, _p_ ~ref~ is the reference pressure, and _q_ ~ref~ is the reference dynamic pressure defined by {latex}\large $$ q_{ref} = {1 \over 2}{\rho_{ref}v_{ref}^2}$${latex} |
The
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reference
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pressure,
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density,
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and
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velocity
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are
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defined
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in
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the
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Reference
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Values
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panel
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in
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Step
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5.
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Let's
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plot
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pressure
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coefficient
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vs
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x-direction
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along
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the
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cylinder.
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Plot
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>
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XY
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Plot...
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Change
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the
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Y
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Axis
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Function
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to
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Pressure
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...
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,
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followed
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by
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Pressure
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Coefficient
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.
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Then, select cylinder under Surfaces.
Click Plot.
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select {color:#660099}{*}{_}cylinder{_}{*}{color} under {color:#660099}{*}{_}Surfaces{_}{*}{color}. \\ !Step6_CpPanel.png! Click {color:#660099}{*}{_}Plot{_}{*}{color}. \\ [!step6_Cpplotsm.jpg!|^step6_Cpplot.jpg] {newwindow:Higher Resolution Image}https://confluence.cornell.edu/download/attachments/104400192/step6_Cpplot.jpg?version=1{newwindow} As can be |
As can be seen,
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the
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pressure
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coefficient
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at
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the
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back
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is
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lower
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than
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the
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pressure
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coefficient
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at
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the
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front
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of
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the
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cylinder.
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The
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irrecoverable
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pressure
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is
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due
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to
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the
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separation
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at
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the
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back
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of
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cylinder
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and
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the
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frictional
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loss.
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Now,
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let's
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take
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a
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look
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at
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the
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Contour
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of
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Pressure
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Coefficient
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variation
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around
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the
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cylinder.
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Display
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>
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Contours
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Under Contours of, choose Pressure.. and Pressure Coefficient. Select the Filled option. Increase the number of contour levels plotted: set Levels to 100.
Click Display.
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https://confluence.cornell.edu/download/attachments/104400192/step6_Cp_contour.jpg?version=1 |
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Because the cylinder is symmetry in shape, we see that the pressure coefficient profile is symmetry between the top and bottom of cylinder.
Plot Stream Function
Now, let's take a look at the Stream Function.
Display > Contours
Under Contours of, choose Velocity.. and Stream Function. Deselect the Filled option. Click Display.
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https://confluence.cornell.edu/download/attachments/104400192/step6_streamline.jpg?version=1 |
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Enclosed streamlines at the back of cylinder clearly shows the recirculation region.
Plot Vorticity Magnitude
Let's take a look at the Pressure Coefficient variation around the cylinder. Vorticity is a measure of the rate of rotation in a fluid.
Display > Contours
Under Contours of, choose Velocity.. and Vorticity Magnitude. Deselect the Filled option. Click Display.
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https://confluence.cornell.edu/download/attachments/104400192/step6_vorticity.jpg?version=1 |
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