Modeling of Flow Passing Backward Facing Step

Abstract

Flows passing sudden diameter expansion of ducts can be found in many industrial situations such as flows in annular spaces between drill pipes and open or cased holes while circulating drilling fluids down the wells and up the annular spaces to surface during oil and gas wells drilling. As a first step towards understanding the flow behavior in situation like theses, a simulation of flows similar to this has been carried out. This paper presents results of a computational study of steady, compressible flow over a backward facing-step in a wide, two dimensional duct. The flow in this duct has been investigated experimentally by previous workers ]1[ and so provides a useful benchmark test case. In the present work the commercial CFD code Fluent v6.0.20 is used to compute results for the range of Reynolds numbers 70 < Re < 7000, where Re is based on two-thirds of maximum velocity and duct height upstream of the step. This range includes the laminar, transitional and low Reynolds number turbulent flow regimes, for which significant variations in the separation length have been measured. The results to be presented will include the variation of velocity distributions and separation lengths for the recirculating flow region downstream of the step with Reynolds number