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lift/drag coefficient and inertial

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Old   January 14, 2007, 02:49
Default lift/drag coefficient and inertial
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When trying to simulate a pure sinusodial pitching airfoil at high frequency of around 6Hz with amplitude of 30deg, I get cl of amplitude 1000+ and cd of 300+. I wonder if the inertial force has already been included in this value and must been subtracted to get the actual force produced.

I am confused because in some papers regarding wind tunnel experiment with a fruitfly, they mention subtracting the inertial force from the measured force. If so, how should the calculation be done.

Lastly, does the gravity "g" play any part in this question? In my simulation, I did not include the "g" term and the NS eqn has been nondimensioned.

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Old   January 14, 2007, 08:57
Default Re: lift/drag coefficient and inertial
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Im pretty sure that the inertial force has been accounted while obtaining the forces. Its true that higher force coefficients are observed for a flapping insect wing such as a bumble bee. I usually dont subtract the inertial forces. For example if u take the case of an implusively accelerated cylinder from rest, the forces that are generated during the initial times are inertial and can be obtained thru a closed form expression based on added mass coefficients. So if one subtracts these forces off, it might not make sense.

If u add 'g', you will have different forces obviously. But thats a different case altoghether.

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