swirl (number) in jet flow
 

I have an equilibrium swirling flow in a coaxial jet with a center flow and a swirling outer flow as inlet conditions (the Roback and Johnson configuration). The flow is assumed to be steady/non-transient for now. Inlet boundary conditions are given in terms of swirl numbers, which are in the range of [0.2, 0.5]. How can this be put into the boundary condition at the inlet?

regards, N.A.Beishuizen