I am modelling the laminar flow in the curved duct of square cross section. My problem is when I use the low Dean number equal 150, I have two counters rotating secondary vortices. Or the critical Dean number in my geometry is 150 since the literature(ie at Dn=150, logically I found four counters rotating secondary vortices) Please give me some help, Thank you.

i am not sure what's problem you meet.do you want two counters rotat the ssecondary vortex?what's mean? please explain in detail,ok?

Thanks for you leon. I want use an UDF to change the hydraulic diameter in the Navier Stokes equations with the channel width of a curved rectangular channel. Happy new year