## Step 6: Analyze Results

#### Lift Coefficient

The solution converged after about 480 iterations.

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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

**. Click**

*Skip***.**

*Display*newwindow | ||||
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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.

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To get white background go to: in Color section. Click Coloring. Click Preview when prompted "NoReset graphics window?" |

newwindow | ||||
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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 | ||||
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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.

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

where *p* is the static pressure,

*P** _{ref}* is the reference pressure, and

*q** _{ref}* is the reference dynamic pressure defined by

Latex |
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\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

**..., followed by**

*Pressure***. Then, select**

*Pressure Coefficient***under**

*airfoil***.**

*Surfaces*Click ** Plot**.

newwindow | ||||
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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

**from under**

*Pressure Coefficient***. Check the**

*Contours Of***and**

*Filled***under**

*Draw Grid***menu. Set Levels to**

*Options*`50`

. Click

**.**

*Display*newwindow | ||||
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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