UNDER CONSTRUCTION

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Author: Daniel Kantor and Andrew Einstein, Cornell University

{color:#ff0000}{*}Problem Specification{*}{color}
[1. Create Geometry in GAMBIT|FLUENT - Turbulent Flow Past a Sphere - Step 1]
[2. Mesh Geometry in GAMBIT|FLUENT - Turbulent Flow Past a Sphere - Step 2]
[3. Specify Boundary Types in GAMBIT|FLUENT - Turbulent Flow Past a Sphere - Step 3]
[4. Set Up Problem in FLUENT|FLUENT - Turbulent Flow Past a Sphere - Step 4]
[5. Solve\!|FLUENT - Turbulent Flow Past a Sphere - Step 5]
[6. Analyze Results|FLUENT - Turbulent Flow Past a Sphere - Step 6]
[7. Refine Mesh|FLUENT - Turbulent Flow Past a Sphere - Step 7]
[Problem 1|FLUENT - Turbulent Flow Past a Sphere - Problem 1]

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h2. Step 6: Analyze Results

For all of our analysis we will be looking at the {color:#660099}{*}{_}Sphere{_}{*}{color} surface under {color:#660099}{*}{_}Surfaces{_}{*}{color}, unless otherwise noted.


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 this figure, we see that there is a region of low velocity and recirculation at the back of cylinder.***************
{info:title=Zoom in the cylinder using the middle mouse button.}
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Now, let's take a look at the Contour of Pressure Coefficient variation around the cylinder.

*Display > Contours*

Under {color:#660099}{*}{_}Contours of{_}{*}{color}, choose {color:#660099}{*}{_}Pressure.._{*}{color} and {color:#660099}{*}{_}Pressure Coefficient{_}{*}{color}. Select the {color:#660099}{*}{_}Filled{_}{*}{color} option. Increase the number of contour levels plotted: set {color:#660099}{*}{_}Levels{_}{*}{color} to {{100}}.

!step6_Cphowto.jpg!

Click {color:#660099}{*}{_}Display{_}{*}{color}.
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[!step6_Cp_contoursm.jpg!|^step6_Cp_contour.jpg]

**********Because the cylinder is symmetry in shape, we see that the pressure coefficient profile is symmetry between the top and bottom of cylinder.*********
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h4. Plot Stream Function

Now, let's take a look at the Stream Function.

*Display > Contours*

Under {color:#660099}{*}{_}Contours of{_}{*}{color}, choose {color:#660099}{*}{_}Velocity.._{*}{color} and {color:#660099}{*}{_}Stream Function{_}{*}{color}. Deselect the {color:#660099}{*}{_}Filled{_}{*}{color} option. Click {color:#660099}{*}{_}Display{_}{*}{color}.
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[!step6_streamlinesm.jpg!|^step6_streamline.jpg]

***********Enclosed streamlines at the back of cylinder clearly shows the recirculation region.*************

h4. Plot Vorticity Magnitude

Let's take a look at the Pressure Coefficient variation around the Sphere. Vorticity is a measure of the rate of rotation in a fluid.

*Display > Contours*

Under {color:#660099}{*}{_}Contours of{_}{*}{color}, choose {color:#660099}{*}{_}Velocity.._{*}{color} and {color:#660099}{*}{_}Vorticity Magnitude{_}{*}{color}. Deselect the {color:#660099}{*}{_}Filled{_}{*}{color} option. Click {color:#660099}{*}{_}Display{_}{*}{color}.

[!step6_vorticitysm.jpg!|^step6_vorticity.jpg]

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 reference pressure, density, and velocity are defined in the *Reference Values* panel in Step 5.

Let's plot pressure coefficient vs x-direction along the cylinder.

*Plot > XY Plot...*

Change the {color:#660099}{*}{_}Y Axis Function{_}{*}{color} to {color:#660099}{*}{_}Pressure{_}{*}{color}{color:#660099}...{color}, followed by {color:#660099}{*}{_}Pressure Coefficient{_}{*}{color}. Then, select {color:#660099}{*}{_}Sphere{_}{*}{color} under {color:#660099}{*}{_}Surfaces{_}{*}{color}.

\\  !Step6_CpPanel.png!

Click {color:#660099}{*}{_}Plot{_}{*}{color}.

\\  [!step6_Cpplotsm.jpg!|^step6_Cpplot.jpg]

We see that there is a lot of scatter in our data, so we will be creating a line along the sphere to try and get a better picture of the pressure coefficient.

 
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***AFTER EXPLANATION OF PLOTTING***

Comparison

With our simulation data, we can now compare the Fluent with experimental data.  Click HERE to download the experimental data. The two sets of data for Pressure Coefficients are shown here:
(INSERT PICTURE). 

The two sets of data for drag coefficient are shown here:

|Experimental | 0.1|
|Simulation | 0.4|




*[*Go to Step 7: Refine Mesh*|FLUENT - Turbulent Flow Past a Sphere - Step 7]*

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