What do you mean by beginning ?  Swirl is zero near axis @ exit not inlet. Actually based on my experiments with fluent , Simulation with very high swirl velocity shows high velocity jump near axis but very low swirl velocity it is actually low.  Relative jump probably will be same but i will check that.  



This plot is obtained from CFD post which i have taken from presentation which i prepared, that's why black bordered.

Mesh i have already been refining , solution also shows convergence is achieved to the order 1e-5. 

That's where is the real problem is, solution shows convergence(residual stagnates) and still we have appreciable velocity jump. 


Aspect ratio : it was below 10

cell volume : i didn't checked but i think i didn't gave any high bias factor which might give high volume change .

Mesh : 480 X 1200, near axis cell height is ~1.5e-4 m