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

h2. Step 6: Analyze Results


h4. Lift Coefficient

The solution converged after about 480 iterations.
{noformat}
   476 1.0131e-06 4.3049e-09 1.5504e-09 6.4674e-01 2.4911e-03  0:00:48  524
!  477 solution is converged
   477 9.9334e-07 4.2226e-09 1.5039e-09 6.4674e-01 2.4910e-03  0:00:38  523
{noformat}
From FLUENT main window, we see that the lift coefficient is 0.647. This compare fairly well with the literature result of 0.6 from [Abbott et al.\|FLUENT - Flow over an Airfoil\- Step 7 #ref\]
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h4. Plot Velocity Vectors

Let's see the velocity vectors along the airfoil.

*Display > Vectors*

Enter 4 next to {color:#660099}{*}{_}Scale{_}{*}{color}. Enter 3 next to {color:#660099}{*}{_}Skip{_}{*}{color}. Click {color:#660099}{*}{_}Display{_}{*}{color}.
\\  !velocity magnitude_sm.jpg!
{newwindow: Higher Resolution Image}https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude.jpg{newwindow}
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As can be seen, the velocity of the upper surface is faster than the velocity on the lower surface.
{tip:title=White Background on Graphics Window} To get white background go to:
*Main Menu > File > Hardcopy*
Make sure that {color:#660099}{*}{_}Reverse Foreground/Background{_}{*}{color} is checked and select {color:#660099}{*}{_}Color{_}{*}{color} in {color:#660099}{*}{_}Coloring{_}{*}{color} section. Click {color:#660099}{*}{_}Preview{_}{*}{color}. Click {color:#660099}{*}{_}No{_}{*}{color} when prompted "_Reset graphics window?_"
{tip}
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\\  !velocity magnitude leading edge_sm.jpg!
{newwindow: Higher Resolution Image} https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude%20leading%20edge.jpg{newwindow}
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On the leading edge, we see a stagnation point where the velocity of the flow is nearly zero. The fluid accelerates on the upper surface as can be seen from the change in colors of the vectors.
\\  !velocity magnitude trailing edge_sm.jpg!
{newwindow: Higher Resolution Image}https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude%20trailing%20edge.jpg{newwindow}
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On the trailing edge, the flow on the upper surface decelerates and converge with the flow on the lower surface.
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{info:title=}Do note that the time for fluid to travel top and bottom surface of the airfoil is not necessarily the same, as common misconception
{info}

h4. Plot Pressure Coefficient

*Pressure Coefficient* is a dimensionless parameter defined by the equation
{latex}
\large
$$
{C_p} = {{(p-p_{ref})} \over q_{ref}}
$$
{latex}
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|FLUENT - Flow over an Airfoil- Step 5]. Please refer to FLUENT's help for more information. Go to {color:#660099}{*}{_}Help > User's Guide Index{_}{*}{color} for help.

*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}{*}{_}airfoil{_}{*}{color} under {color:#660099}{*}{_}Surfaces{_}{*}{color}.

!pressure coefficient menu.jpg!

Click {color:#660099}{*}{_}Plot{_}{*}{color}.
\\  !pressure coefficient plot_sm.jpg!\\
{newwindow:Higher Resolution Image}https://confluence.cornell.edu/download/attachments/90744040/pressure%20coefficient%20plot.jpg{newwindow}
The lower curve is the upper surface of the airfoil and have a negative pressure coefficient as the pressure is lower than the reference pressure.

h4. Plot  Pressure Contours

Plot static pressure contours.

*Display > Contours...*

Select {color:#660099}{*}{_}Pressure..._{*}{color} and {color:#660099}{*}{_}Pressure Coefficient{_}{*}{color} from under {color:#660099}{*}{_}Contours Of{_}{*}{color}. Check the {color:#660099}{*}{_}Filled{_}{*}{color} and {color:#660099}{*}{_}Draw Grid{_}{*}{color} under {color:#660099}{*}{_}Options{_}{*}{color} menu. Set Levels to {{50}}.
\\  !presssure coefficient contour menu.jpg!
Click {color:#660099}{*}{_}Display{_}{*}{color}. &nbsp;
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\\  !presssure coefficient contour plot_sm.jpg!\\
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{newwindow:Higher Resolution Image}https://confluence.cornell.edu/download/attachments/90744040/presssure%20coefficient%20contour%20plot.jpg{newwindow}
&nbsp;
From the contour of pressure coefficient, we see that there is a region of high pressure at the leading edge (stagnation point) and region of low pressure on the upper surface of airfoil. This is of what we expected from analysis of velocity vector plot. From Bernoulli equation, we know that whenever there is high velocity, we have low pressure and vise versa.&nbsp;
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Go to [Step 7: Refine Mesh|FLUENT - Flow over an Airfoil- Step 7]

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