1. While meshing a sector i have skewness near 0.9-0.95 at the axis,  will it be a problem ? How to reduce it's skewness.

2. Also orthogonality at the axis is also bad near 0.08 , is it problem ? How to rectify it ?

3. How to decide the angle of rotation of a sector , for now i have 2 deg but what is procedure / strategy to decide one.

4. First order upwind scheme gives convergence upto 1e-6 but second order upwind scheme only gives convergence upto 1e-2 - 1e-3 and rest other variables converges to 1e-6. What could be the problem ? Please note second order upwind scheme are preferred for swirl flow.

Here you can check 2d form of the  Computational domain .

I just rotated the geometry by 2 deg angle about the axis in ansys geometry

Dimensions :

L : 42 cm ,

L1 : 35 cm

Re : 2.8 cm Ro : 7 cm H : 0.8*L(point of interest,irrelevant for computation)

General :  3D , pressure based solver, steady

Model : RSM, Linear pressure strain, Non-Equilibrium wall function

Material : Air

Boundary condition :

Inlet : Velocity inlet :  9.26 m/s (4.634 m/s radial velocity, 8.026 m/s swirl velocity)

outlet : outflow  Faces : periodic BC  wall : No slip

Scheme : SIMPLE, PRESTO! for pressure Controls : 0.5 for momentum

Initialization  : Hybrid