Three-dimensional forced convection flow adjacent to backward-facing step

Numerical simulations of three-dimensional laminar forced convection flow adjacent to a backward-facing step in a duct are presented for the case where the duct's aspect ratio is eight (AR = 8), its expansion ratio is two (ER = 2), and the step height S is 1.00 cm. This relatively small aspect ratio duct was selected to increase the significance of the three-dimensional flow on the heat transfer downstream from the step. The flow upstream of the step is treated as fully developed and isothermal. The duct walls are treated as adiabatic surfaces with the exception of the stepped wall that is downstream from the step that is treated as being heated with uniform heat flux. Complex three-dimensional flow develops downstream from the step with a primary recirculation flow region and a reattachment length that has a minimum in its spanwise distribution near the sidewall. A spanwise swirling flow (vortex) develops inside the primary recirculation flow region and a reverse flow region develops near the sidewall. These three-dimensional features increase in size with increasing Reynolds number. The jetlike flow that develops near the sidewall within the separating shear layer impinges on the stepped wall causing I minimum to develop in the reattachment length and a maximum to develop in the Nusselt number near the sidewall, The distributions of the three velocity components, reattachment length, friction coefficient, and Nusselt number are presented and discussed.