A numerical revisit of backward-facing step flow problem

In the present study we take a fresh look at a laminar flow evolving into a larger channel through a step configured in a backward-facing format. We c onduct steady three-dimensional Navier-Stokes flow analysis in the channel using the step geometry and flow conditions reported by Armaly et nl. This allows a direct comparison with the results of physical experiments, thus s erving to validate the numerical results computed in the range of 100 less than or equal to Re less than or equal to 1000. Results show that there is generally excellent agreement between the present results and the experimen tal data for Re = 100 and 389. Fair agreement for Re = 1000 is also achieve d, except in the streamwise range of 15 less than or equal to x less than o r equal to 25. The main difference stems from the fact that the roof eddy i s not, extended toward the midspan in the channel with a span width 35 time s of the height of the upstream channel. In the present study we also revea l that the how at the plane of symmetry develops into a two-dimensional-lik e profile only when the channel width is increased up to 100 times of the u pstream step height for the case with Re = 800. The present computational r esults allow the topological features of the flow to be identified using cr itical point theory. The insight thus gained is useful in revealing a mecha nism for the development of an end-wall-induced three-dimensional vortical flow with increasing Reynolds number. (C) 1999 American Institute of Physic s. [S1070-6631(99)00704-7].