Abstract
Direct numerical simulation results of the three-dimensional separated flow and heat transfer around a backward-facing step of channel expansion ratio 1.5 and step aspect ratio 36.0 are presented. The finite differnce method was used in the Reynolds number Re from 300 to 1000. The flow is steady up to Re=500 accompanying the longitudinal vortices near the side walls, bringing about heat transfer enhancement there. The flow becomes unsteady at Re=700, resulting in the maximum Nusselt number in the channel central region far downstream of the time averaged reattachment point. At Re=1000, a severely complicated unsteady three-dimensional flow brings about a complex thermal field. The importance of the three-dimensional calculation of the unsteady flow is presented even in a very large step aspect ratio.
