The effect of forced flow on turbulent natural convetion adjacent to a vertical backward-facing step

摘要

Turbulent mixed convection adjacent to a two dimensional, vertical backward-facing step is predicted numerically to explore the effect of forced flow velocity on turbulent natural convection. A two-equation k-#epsilon# tubulence model is utilized in the numerical simulation. Computations are performed for air with a Prandtl number of 0.71 for a step height of 2.2 cm and a temperature difference of 30 deg C between the heated upstream and downstream plates and the free steam. The efects of increasing the forced flow velocity on the reattachment length, the local Nusselt number, the mean velocity and temperature distributions, the turbulent kinetic energy and its dissipation rate are examined. The computational results have revealed that the introduction of small forced flow velcoities (0.1 approx 1.0 m/s) to an existing turbulent natural convection flow suppresses the turbulence intensity, decreases the heat transfer rate from the wall, and delays the transition location from laminar to turbulent flow. An interesting feature is that the turbulent natural convection flow changes from buoyancy-dominated turbulent mixed convection to laminar mixed convection and that is followed by turbuent force convection as the forced flow velocity increases beyond 1.0 m/s.