FLOW IN A PIPE WITH A RING-TYPE OBSTACLE

Turbulent calculations have been carried out to investigate flows in a circular pipe with a ring-type obstacle attached to the wall for Reyn olds numbers from 10(2) to 10(5). The numerical procedure is based on the solution of the primitive variable formulation of the Reynolds-ave raged Navier-Stokes governing equations and the k - epsilon turbulence model in axisymmetric co-ordinate system and with a non-staggered gri d. The obstacle opening ratio (d/D) is 0.5, and the obstacle thickness ratio (h/D) is 0.13. The numerical results reveal the effect of the R eynolds number on the flow fields. With the Reynolds number varying fr om 10(2) to 10(5), the reattachment length (Z(r)/D) increases to a max imum of 3.1 at Re = 5 x 10(2) and then decreases gradually to a value of 2.1. The velocity profiles of the fully developed flow change from parabolic to power-law curves. The non-dimensional maximum turbulent s hear stress (tau(max)) varies in a range from 0.2 to 0.4 and the press ure loss (P-loss) across the obstacle varies between 8.0 and 11.0, whi le the maximum vorticity (Omega(max)) remains unchanged at a value of 16.2. At Re = 5 x 10(2) and 10(3), laminar cores exist downstream of t he obstacle. For the cases of Re > 3 x 10(4), the tau(max) and P-loss remain unchanged at 0.32 and 10.5, respectively. The how field structu res are similar. The distributions of the centreline turbulent kinetic energy, velocity and pressure along axial distance remain unchanged.