I am trying to simulate the highly swirl flow in confined tube using axi-symmetric swirl (2D geometry).

Version : 2019 R3,R2,R1 (all gives same)

Geometry : 150mm (dia)X 6145 mm(length) rectangle (axisymmetric cylinder)

Working fluid : Air

Model : RSM , stress-omega

solver : Pressure based

Type : Steady

scheme : SIMPLE for coupling , PRESTO for pressure , SOU's for other

Reynolds no : 50 K

Inlet : Velocity profile (axial,radial, swirl)

outlet : Pressure outlet ( Avg pressure = 0)

I am unable to get zero velocity at the axis when RSM is employed but this kind of problem is not there with other turbulence models. Please help.