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  • FLUENT - Flow over an Airfoil- Step 7

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Main Menu > Report > Forces...


Select Forces. Under Force Vector, enter 0.9998 next to X. Enter 0.02094 next to Y. Select airfoil under Wall Zones. Click  Print.

Here's is what we see in the main menu:

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Info
title

In reality, (Cd)skin friction has biggest contribution to drag but ignored because of the inviscid model that we specify. (Cd)pressure should be zero, but not because of inaccuracies and numerical dissipation.

Now, let's look at the lift coefficient.

Main Menu > Report > Forces...

Select Forces. Under Force Vector, enter -0.02094 next to X. Enter 0.9998 next to Y. Select airfoil under Wall Zones. Click  Print.

Here's is what we see in the main menu:

No Format

Force vector: (-0.02094 0.99980003 0)
                                pressure        viscous          total       pressure        viscous          total
zone name                          force          force          force    coefficient    coefficient    coefficient
                                       n              n              n
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
airfoil                        1008.3759              0      1008.3759      0.6585058              0      0.6585058
------------------------- -------------- -------------- -------------- -------------- -------------- --------------
net                            1008.3759              0      1008.3759      0.6585058              0      0.6585058

 

Similarly, lift force is due to the contribution of pressure force and viscous force.

Cl =  (Cl)pressure + (Cl)skin friction

where

(Cl)pressure is due to pressure force.

(Cl)skin friction is due to viscous force.

Since our model is inviscid, (Cl)skin friction is zero. We see that the lift coefficient compare well with the experimental value of 0.6.

Info
title

Do note that the lift coefficient for inviscid model is higher than the experimental value. In reality, if we take into account the effect of viscosity, we will have (Cl)skin friction of negative value. The viscous effect will lower the overall lift coefficient. Since our inviscid model neglect the effect of viscosity, we have a slightly higher lift coefficient compared to the experimental data.



Before we can make any conclusion about the accuracy of our result, we should always make validation check. The most common validation step is grid convergence check.

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