Anyone have used or using UDF for defining Cd for speheres in a gas-particle flow...? In other words anyone has used DEFINE_DPM_DRAG, given by fluent...?

I have a question/doubt in that UDF.

Fluent wants the user to return a non-dimensional number as drag number, which is equivalent to 18*Cd*Re/24. But how does a drag force be dimensionless....If it is Cd it makes sense...but how a drag force is non-dimensionless...?

Please clarify!

I have written UDFs using DEFINE_DPM_DRAG. That macro must return a value for (18*Cd*Re/24) to Fluent. The drag force is then calculated as FD = (18*Cd*Re/24)*(my/(rho_p*d_p^2)), as stated in the Fluent manual. This might seem a bit strange but it does not cause you any problems, really? As both Cd and Re_p are dimensionless, the product (18*Cd*Re/24) is of course also dimensionless.

/Henrik