##### Child pages
• FLUENT - Flow over an Airfoil- Step 6

# Page History

## Key

• This line was removed.
• Formatting was changed.
Comment: Migration of unmigrated content due to installation of a new plugin

## Step 6: Analyze Results

#### Lift Coefficient

The solution converged after about 480 iterations.

No Format
   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


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.

#### Plot Velocity Vectors

Let's see the velocity vectors along the airfoil.

Display > Vectors

Enter 4 next to Scale. Enter 3 next to Skip. Click Display.

newwindow
 Higher Resolution Image Higher Resolution Image
https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude.jpg

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 Reverse Foreground/Background is checked and select Color in Coloring section. Click Preview. Click No when prompted "Reset graphics window?"

newwindow
 Higher Resolution Image Higher Resolution Image
 https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude%20leading%20edge.jpg

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.

newwindow
 Higher Resolution Image Higher Resolution Image
https://confluence.cornell.edu/download/attachments/90744040/velocity%20magnitude%20trailing%20edge.jpg

On the trailing edge, the flow on the upper surface decelerates and converge with the flow on the lower surface.

Info

Do note that the time for fluid to travel top and bottom surface of the airfoil is not necessarily the same, as common misconception

#### Plot Pressure Coefficient

Pressure Coefficient is a dimensionless parameter defined by the equation

Latex
\large
$${C_p} = {{(p-p_{ref})} \over q_{ref}}$$


where p is the static pressure,

Pref is the reference pressure, and

qref is the reference dynamic pressure defined by

Latex
\large
$$q_{ref} = {1 \over 2}\rho_{ref}{v_{ref}}^2$$


The reference pressure, density, and velocity are defined in the Reference Values panel in Step 5. Please refer to FLUENT's help for more information. Go to Help > User's Guide Index for help.

Plot > XY Plot...

Change the Y Axis Function to Pressure..., followed by Pressure Coefficient. Then, select airfoil under Surfaces.

Click Plot.

newwindow
 Higher Resolution Image Higher Resolution Image
https://confluence.cornell.edu/download/attachments/90744040/pressure%20coefficient%20plot.jpg

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.

#### Plot Pressure Contours

Plot static pressure contours.

Display > Contours...

Select Pressure... and Pressure Coefficient from under Contours Of. Check the Filled and Draw Grid under Options menu. Set Levels to 50.

Click Display.

newwindow
 Higher Resolution Image Higher Resolution Image
https://confluence.cornell.edu/download/attachments/90744040/presssure%20coefficient%20contour%20plot.jpg

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.

Go to Step 7: Refine Mesh

See and rate the complete Learning Module