Three-Dimensional Forced Convection Flow Adjacent to Backward-Facing Step

Abstract

Numerical simulations of three-dimensional laminar forced convection e ow adjacent to a backward-facing step in a ductare presented forthecase wheretheduct’ s aspect ratio iseight (AR= 8), itsexpansion 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 signie cance of the three-dimensional e ow on the heat transfer downstream from the step. The e ow 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 e ux. Complex three-dimensional e ow develops downstream from the step with a primary recirculation e ow region and a reattachment length that has a minimum in its spanwise distribution near the sidewall. A spanwise swirling e ow (vortex) develops inside the primary recirculation e ow region and a reverse e ow region develops nearthe sidewall. These three-dimensional features increase in size with increasing Reynolds number. The jetlike e ow that develops near the sidewall within the separating shear layer impinges on the stepped wall causing a 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 coefe cient, and Nusselt number are presented and discussed.