Computation of three dimensional subsonic flows in ducts using the PNS approach.

The laminar three dimensional flow in curved ducts of square cross section is analyzed for an incompressible viscous fluid. The flowfield is modelled using the parabolized Navier-Stokes equations. This model enables a marching procedure in main stream direction to be used, which means less computer memory and time than solving the full Navier-Stokes equations. Three momentum equations and the equations for crossflow velocity correction and pressure field have been solved numerically using the LSOR method. Computations are performed for developing laminar flow in straight, curved and S-shaped ducts of square cross section for various Reynolds numbers and radii of curvature. The main and secondary velocity fields and the pressure are examined. Inclusion of an a priori determined inviscid pressure field in the analysis improves the accuracy of the computations and their agreement with measurements. Detailed comparisons of results for an S-bend duct of square cross section with experiment are presented with and without the inviscid pressure term. Computations for the S- bend geometry start from its upstream straight part using uniform inlet flow conditions, so no initial conditions are required when the curved part is reached. (English abstract)