Turbulent Forced Convection in a Plane Asymmetric Diffuser: Effect of Diffuser Angle

Abstract

A simulation of two-dimensional turbulent forced convection in a plane asymmetric diffuser with an expansion ratio of 4.7 is performed, and the effect of the diffuser angle on the flow and heat transfer is reported. This geometry is common in many heat exchanging devices, and the turbulent convective heat transfer in it has not been examined. The momentum transport in this geometry, however, has received significant attention already, and the studies show that the results from the υ2¯‐f type turbulence models provide better agreement with measured velocity distributions than that from the k‐ε or k‐ω turbulence models. In addition, the υ2¯‐f type turbulence models have been shown to provide good heat transfer results for separated and reattached flows. The k‐ε‐ζ (υ2¯‐f type) turbulence model is used in this study due to its improved numerical robustness, and the FLUENT-CFD code is used as the simulation platform. User defined functions for the k‐ε‐ζ turbulence model were developed and incorporated into the FLUENT-CFD code, and that process is validated by simulating the flow and the heat transfer in typical benchmark problems and comparing these results with available measurements. This new capability is used to study the effect of the diffuser angle on forced convection in an asymmetric diffuser, and the results show that the angle influences significantly both the flow and the thermal field. The increase in that angle increases the size of the recirculation flow region and enhances the rate of the heat transfer.