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Induced drag, pressure drag, viscous drag.

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Old   August 22, 2015, 07:41
Default Induced drag, pressure drag, viscous drag.
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aleix de toro diaz
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I am having problems understanding the fluent results regarding the drag obtained by fluent (pressure drag and viscous drag).

Pressure drag and viscous drag comes form the parasite drag. Induced drag is not related to pressure drag neither viscous drag because it is related to the generation of lift.

So how can I obtain the induced drag with fluent?

I have read that by having the value of drag with 0 lift, and subtracting the value of drag at another angle of attack, it will give the induced drag. I don't thing this solution is accurate.

Does someone know how to do that?

Many thanks
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Old   August 24, 2015, 12:13
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Lucky Tran
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The total drag is the sum of parasitic drag and induced drag. The parasitic drag is the sum of pressure and viscous drag. You just need to subtract the parasitic drag from the total drag to get the induced drag, maybe.

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Originally Posted by aleix.de.toro View Post
I have read that by having the value of drag with 0 lift, and subtracting the value of drag at another angle of attack, it will give the induced drag. I don't thing this solution is accurate.
You can also use this method. However, the turning of the airfoil is "conceptual". You do not actually test the airfoil at another angle of attack. The task is to find the vector projection of the effective lift (the lift that is perpendicular to the effective airflow) with the actual vertical lift. The difference between these two vectors is the induced-drag, the drag that arises because the effective lift force is partially aligned with the drag direction.
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Old   August 24, 2015, 18:00
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aleix de toro diaz
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Thanks for the answer luckytran.

The problem is that fluent only gives the results of pressure and viscous drag (parasite drag), not the total drag. So the induced drag does not appears anywhere.

And for the other method, how could fluent gives the vector projection of the effective lift?
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