Flow in a pipe with a ring-type obstacle

Abstract

Turbulent calculations have been carried out to investigate flows in a circular pipe with a ring-type obstacle attached to the wall for Reynolds numbers from 102 to 105. The numerical procedure is based on the solution of the primitive variable formulation of the Reynolds-averaged Navier-Stokes governing equations and the k - ε turbulence model in axisymmetric co-ordinate system and with a non-staggered grid. 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 Reynolds number on the flow fields. With the Reynolds number varying from 102 to 105, the reattachment length (Zr/D) increases to a maximum of 3.1 at Re = 5 × 102 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 shear stress (τmax) varies in a range from 0.2 to 0.4 and the pressure loss (fioss) across the obstacle varies between 8.0 and 11.0, while the maximum vorticity (Ωmax) remains unchanged at a value of 16.2. At Re = 5 × 102 and 103, laminar cores exist downstream of the obstacle. For the cases of Re>3 × 104, the τmax and Ploss remain unchanged at 0.32 and 10.5, respectively. The flow field structures are similar. The distributions of the centreline turbulent kinetic energy, velocity and pressure along axial distance remain unchanged.