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  • FLUENT - Flow over an Airfoil- Step 6

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Panel

Problem Specification
1. Create Geometry in GAMBIT
2. Mesh Geometry in GAMBIT
3. Specify Boundary Types in GAMBIT
4. Set Up Problem in FLUENT
5. Solve!
6. Analyze Results
7. Refine Mesh
Problem 1
Problem 2

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 > VectorsUse the default setting by clicking

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

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As can be seen, the velocity of the upper airfoil surface is faster than the velocity on the lower airfoil.

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surface.

Tip
titleWhite 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?"



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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. 
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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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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 Image Removed where  Image Removed
 Latex
where p is the static pressure, Image Removed
Pref is the reference pressure, and  Image Removedand
qref is the reference dynamic pressure defined by Image Removed
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 . 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.
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Click Plot. 
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The lower curve is the The negative part of the plot is 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 Static Pressure Coefficient from under Contours Of. Click Display. Check also the Filled and Draw Grid under Options menu. Set Levels to 50. 
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 From the contour of pressure coefficientFrom the figure, we see that in one grid, there is no more than 3 different pressure contours which suggests that our mesh is fine enough.How can we compare the pressure contour with velocity vector plot? We see that the pressure a region of high pressure at the leading edge (stagnation point) and region of low pressure on the upper surface is negative while the velocity on the upper surface is higher than the reference velocity. Whenever 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 vectors, we have low pressures pressure and vise versa. The phenomenon that we see comply with the Bernoulli equation.
Comparisons
With our simulation data, we can now compare the Fluent with experimental data. The summary of result is shown in the table.
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 FLUENT 
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 Theory 
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Go to Step 7: Refine Mesh
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