Mass flow rate: calculation v/s computation
Hi all,
In my simulations density (Rho) is constant. I have computed mass flow rate (M) through an interior face using standard mass flow rate calculation option from fluent. Then I calculated mass averaged velocity (Vm), area weighted averaged velocity (Va) and facet averaged velocity (Vf). To recheck, I calculated the mass flow rate as M' = Rho*A*V. By using all the three above mentioned velocities in the above formula I am not able to get both mass flow rates the same (i.e. M' and M are not equal). Which is the apropriate value of velocity that one should consider to recalculate accurately the mass flow rate? I guess, the mass flow rate is computed in fluent as summation of (Rho*A*V) values at all the facets. Could any body throw some light on this issue? Thanks. aditya 
Hi beguxa, I believe the velocity you want to use is actually the axial velocity. When running my current simulation of flow rate through a nozzle I used surface integrals in the report menu to get an accurate reading but when calculating the flow through use of a custom field function the velocity which returned the same value for flow rate was the axial velocity.

you can use standard massflow option in fluent. but to check this use velocity normal to the surface in your calculation. I think both should agree.

Dear beguxa
If you define a variable in the Define> Custom Field Functions... as Density*Velocity, and then integrated this variable in the report>surface integral using the "integral" in the "Report type" you can observe that this value is equal to the mass flow rate in your desired surface, which is reported by FLUENT post processing from Report> FLuxes 
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