Effects of stagnating and thermal shielding of an upstream promoter on forced convection of flow past a square cylinder in a channel

Abstract

Abstract This work performs a direct simulation on forced convection heat transfer of flow past a square cylinder in a channel with an upstream promoter. The promoter is small in size that the incoming flow is stagnated and heated, thus the flow in the gap between the promoter and main cylinder keeps steady and the heating by the main cylinder gets weak as it develops downstream. The objective of the present study is to explore the effects of two parameters, i.e., Reynolds number and gap ratio, on the thermal and flow characteristics for Re\u2009=\u200970-140 and GR\u2009=\u20092-8. The effects of the two parameters are presented and analyzed by the thermal and flow fields, variations of global characteristics quantities, local heat transfer characteristics, patterns of flow in the gap and near-wake region, and temperature on the channel walls. We emphasize both time-averaged and fluctuating quantities to reflect the mean and pulsating characteristics of the flow. Numerical results reveal that although the promoter produces a steady flow in the gap, it alters the velocity profile of the gap flow and consequently changes the shearing properties, thus influences the flow around and even in the wake downstream of the main cylinder. In general, the small promoter partially stabilizes the wake flow and reduces the amplitude of fluctuating forces acting on the main cylinder compared with the single cylinder configuration, and the stabilization is more remarkable for small gap ratios. However, the fluctuation of heat transfer rate on the surface of main cylinder may increase. A further analysis indicates that as the promoter is placed close to the main cylinder, the recovery rate of deficit wake flow is slower and the fluctuating amplitude of velocity and temperature is relatively smaller due to the stabilized flow.