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rotation velocity of a water wheel and rotating domain

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Old   November 12, 2014, 10:50
Default rotation velocity of a water wheel and rotating domain
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Hy everybody.

I am simulating a water wheel with an angular velocity v [rad/s].

1) I have imposed the velocity v in "cell zone conditions", both in the reference frame, both in the mesh motion.
When I plot "Graphic and Animation-Contours-velocity magnitude", if there is no water inside the wheel, so only air, the velocity w in a certain point must be w=v*R, where R is the distance between the point and the rotation axle. But the plotted velocity is w=2*v*R and I can't understand why. I have to impose only the rotational velocity v in the mesh motion? if yes, why? It is strange because even if the tangential velocity appears to be wrong w=2*v*R, instead the actual one w=v*R, the wheel makes a complete turn of 360=6.28rad in time=6.28/v, so v is right. How it is possible that w is calculated badly, while the wheel rotates at the right velocity v?

2) If there is no water, the static pressure is only due to the air weight, so it increase from the top of the wheel toward the lowest point of the wheel (since the air is lightweigh the difference of static pressure has to be small, but if I plot it the difference is 300 N/mq!! And the wheel is only 2 m in diameter.

Thank you very much
I hope in some advises
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mesh motion, reference frame, rotating domain, turbine, water wheel

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