angular momentum in swirling flows

[rt1980a]

Hi, I am working with CFD to analyze a swirling burner with a square section combustor. When I calculate the angular and the axial momentum inside the combustor, it decreases the more I check downstream to the burner exit. Do you know what would create a decrease in the angular and axial momentum inside a square section combustor? Should the swirl number variate inside the combustor?

 

Thank you very much for your help.

[Bignose]

Unless there is a source for the angular momentum, wouldn't the fluid's own viscosity slow the swirl down. Your coffee doesn't swirl forever when you mix the sugar into it.