# Drag coefficient CEL expression

 Register Blogs Members List Search Today's Posts Mark Forums Read

 September 27, 2017, 16:55 Drag coefficient CEL expression #1 Member   cfxtwophaseflow Join Date: Aug 2017 Posts: 46 Rep Power: 8 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.

September 28, 2017, 02:48
#2
Senior Member

Lance
Join Date: Mar 2009
Posts: 669
Rep Power: 22
Quote:
 Originally Posted by sarrazs 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?

 September 28, 2017, 10:21 #3 Member   cfxtwophaseflow Join Date: Aug 2017 Posts: 46 Rep Power: 8 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