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general momentum source in cylindrical direction

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Old   May 31, 2006, 08:32
Default general momentum source in cylindrical direction
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Atit
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I'm modeling the turbine in pipe using actuator disc with wake rotation. I use 'Expression' to enter CEL in CFX-Pre. I define Smt, Smr, and Sma as the momentum source in tangential, radial, and axial direction, respectively. For example, Smt=-density*v*a/r. The axial direction coincide to the y-axis.

I use the 'General Momentum Source' with 'Cylindrical Componets' option. At 'Axis Definition' of 'Sources' tab, I choose 'Global Y' as the rotation axis.

However examining vector plot and contour plot from CFX-POST suggests that 'r' that I enter in 'Expression' might not be sqrt(x*x+z*z). Is this possible? and if it is, how can I fix this problem.
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Old   May 31, 2006, 09:05
Default Re: general momentum source in cylindrical directi
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opaque
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Dear Atit,

From the manual, r = sqrt(x*x+y*y) regardless of your axis.. r is the radial coordinate on the local frame where theta is measured from x and z is the axis.

If you want to access the cylindrical coordinates from an axis defintion you must use any of the triplets (raxis,taxis,aaxis). taxis is only available if you defined the axis using any of the local frame coordinate axis. This appeared in ANSYS CFX-10.0.

Hope this helps,

Opaque
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