flow in perforated pipe distributor
 

hello all

Could anyone tell how to model fluid flow in perforated pipe distributor. The perforated pipe is to inject hot air and mix it with a cold air stream flowing perpendicular to axis of the perforated pipe.
The pipe is 300mm in diameter with 30mm diameter of hole and 10mm gap between the holes. There are cca. 880 of the holes on the pipe.
The pipe is sideways insererted in the larger duct.

I tried to model the perforation (in fluent) with porous jump using inertial loss therm alone (C2) neglecting permeability.
For the actual configuration of the holes C2 is cca. 450 (comutated according to fluent help) and fluid flow computation shows quite huge maldistribution of mas flow rate along length of the perforated pipe.

The task is to evenly distribute the flow. I tried to increase C2 to cca 5000, simulating smaler holes with higher resistant to flow, but the result show almost the same maldistribution.
Even higher values of C2 (50000) causes divergence.

What should be appropriate model for perforated pipe distributor or setting for porous jup model? (apart from detail gridding and flow modelling out of every hole)

thanks.