Large eddy simulation of separated flow to investigate heat transfer characteristics in an asymmetric diffuser subjected to constant wall heat flux

Abstract

In the present study, heat transfer characteristics of an asymmetric diffuser with separated flow has been studied. The flow separation is triggered due to wall expansion in two directions. Large Eddy Simulation (LES) approach is adopted to solve the turbulent separated flow and heat transfer in such diffuser at Reynolds number of 10000. For this purpose, a finite volume solver is extended in the OpenFOAM framework to solve the energy equation for incompressible flow. The extended solver has been adjusted to deal with backscatter phenomena and to prevent non-physical heat transfer results and numerical instability. An appropriate grid resolution is employed to perform LES calculations and predict the characteristics of the heat transfer within the separated flow. The numerical results are validated against measurements and Direct Numerical Simulation (DNS) results. The present study showed that the low mean velocity and turbulent kinetic energy (TKE) in a separated flow region are responsible for generating high temperature hot spots resulted from significant reduction of heat transfer from the walls. It has been observed that the heat transfer from the wall is increased slightly before the flow re-attachment region. The applicability of the Reynolds analogy in the separated flow zone for this problem has been examined. Moreover, the analysis of the computational performance showed that increasing the number of computational cells can improve, to certain extent, the convergence rate of the solver and therefor, reduced the computation cost.