Large eddy simulation of flow and heat transfer in a channel with a detached rib array

Ribbed channels are widely used to enhance heat transfer in various heat exchange equipment. However, the heat transfer is locally deteriorated immediately behind the rib due to the flow separation. To overcome this shortcoming, a detached rib array has been proposed recently. In the present study, large eddy simulations (LES) of turbulent flow and heat transfer in a channel with a detached rib array have been conducted. The no-slip and no-jump conditions on the rib surface are satisfied in the Cartesian coordinates by using an immersed boundary method. Experiments are conducted as well to validate the simulation. The velocity and temperature fields are obtained by a hot wire and a thermocouple, respectively. The surface heat transfer is measured using the thermochromic liquid crystal with a high spatial resolution. Compared with the attached rib, the detached one enhances the heat transfer underneath the rib, whereas the channel wall downstream of the rib shows lower heat transfer rate. By investigating the effect of the clearance between the rib and the wall, we have found an intermediate flow pattern, where the counter-rotating vortex pair and the separation bubble coexist. Including the new flow pattern, we discuss the flow characteristics such as the wake length and the locus of the saddle points, and the flow physics behind the local heat transfer distribution on the channel wall based on the instantaneous flow and thermal fields. The turbulence data near the solid surface are also presented, which have not been provided by previous experiments.