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Drag coefficient CEL expression

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Old   September 27, 2017, 16:55
Default Drag coefficient CEL expression
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cfxtwophaseflow
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Hi,
I'm doing CFD for an air-water bubble column. I'm using Euler-Euler Model with no turbulence model. I want to use a user drag coefficient example Mei coefficient.
I defined :
relative velocity: Ur = sqrt((air. u-Water. u)^2+(air. v-Water. v)^2+(air. w-Water. w)^2)
Volume fraction : epsilon = air.vf
Reynolds number : Re = 2*Water.density*Ur*air.mean particle diameter/Water.viscosity+10^-17 (10^-17 is just to avoid zero division).
Drag coefficient CD= (16/Re)*(1+(2/((16/Re)+(3.315/sqrt(Re))+1))).
I'm getting this error :
+-------------------------------------------------------------------
| ERROR #001100279 has occurred in subroutine ErrAction.
| Message:
| Floating point exception: Overflow

| ERROR #001100279 has occurred in subroutine ErrAction.
| Message:
| Stopped in routine FPX: C_FPX_HANDLER

For the Ishii Zuber coefficient, which already exists in cfx, works great but not with the CEL expression Mei coefficient.
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Old   September 28, 2017, 02:48
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Lance
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Quote:
Originally Posted by sarrazs View Post
Reynolds number : Re = 2*Water.density*Ur*air.mean particle diameter/(Water.viscosity+10^-17) (10^-17 is just to avoid zero division).
if you want to avoid division by zero you should add the parenthesis in bold - but why would Water.viscosity be zero?
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Old   September 28, 2017, 10:21
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Thank you Lance for your reply. I added 10^-17 to the reynold number not the viscosity. Initially, all velocities are zero and it may be at on point Ur=0 so I want to avoid zero division in the drag coefficient CD
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