angular momentum with swirling flow
 

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.