Three-Dimensional Forced Convection Flow in Plane Symmetric Sudden Expansion

Simulations of three-dimensional flow and heat transfer in laminar incompressible forced convection in plane symmetric sudden expansion (backward-facing step in rectangular duct) are presented for different Reynolds numbers. The duct\u27s downstream (H) and upstream (h) heights are 0.04m and 0.02m, respectively, thus providing a step height (S) of 0.01m and an expansion ratio of 2. The duct\u27s width (W) is 0.08m, thus resulting in an aspect ratio of 4 before and 2 after the expansion, respectively. The incoming flow is considered to be isothermal, hydro-dynamically steady and fully developed. Uniform and constant heat flux is specified on the stepped walls, while the other walls are treated as adiabatic surfaces. The flow appears to be symmetric for the low Reynolds number range that is considered in this study (Re = 150). A “jet-like” flow develops near the sidewall and its impingement on the stepped wall creates a swirling flow inside the primary recirculation region adjacent to the stepped wall, and that is responsible for creating a maximum in the Nusselt number distribution. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped wall does not coincide with the location of the outer edge of the primary recirculation region, especially in the region near the sidewall. Neither one of these boundary lines represents the reattachment region of the separated flow in the region adjacent to the sidewall. The maximum Nusselt number on the stepped wall is located inside the primary recirculation region and is not identical to the “jet-like” flow impingement point. The maximum friction coefficient on the stepped wall is located inside the primary recirculation region, and it is at the center of the duct for the Reynolds number range considered in this study. The minimum friction coefficient on the stepped wall is located at the impingement of the “jet-like” flow