Abstract
Using the standard κ — ε turbulence model, an incompressible, axisymmetric turbulent flow with a sudden expansion was simulated. Effect of upstream hydrodynamic development on flow and heat transfer characteristics downstream of the expansion was investigated. Different hydrodynamic developments were attained by varying the small pipe length-to-diameter ratio, L/d. The simulation revealed circulation downstream of the expansion. A secondary circulation (corner eddy) was also predicted. The maximum Nusselt number was shown to increase with hydrodynamic development, up to 14% for L/d = 30 (fully developed condition) compared to L/d = 5. Similalry, maximum turbulence kinetic energy was found to increase up to 8%. Flow development was shown to affect both magnitude of wall friction and reattachment length. With increasing flow development, there was an increase in wall friction downstream of the reattachment point and a decrease of the reattachment length by a maximum of 7% and one step height, respectively. Effect on turbulence kinetic energy was shown to vanish downstream of the reattachment point.