Buoyancy-driven turbulent convection in a bundle of vertical heated cylinders

etc15 Tracking Number 145

Buoyant, turbulent convective heat transfer around cylindrical rods arranged in bundles is a technically relevant heat transfer configuration which finds application in steam generators, cooling of reactor core fuel assemblies and heat exchangers in general. Most of the research performed so far considered forced convection conditions on vertical rod bundles, corresponding for example to the configuration of a nuclear reactor primary loop. Fewer works have focused on the effect of buoyancy, with or without an external source of momentum. This paper reports a Direct Numerical Simulation study of the fully developed, mixed convection in a bundle of vertical, heated cylinders, where each cylinder releases an equal, uniform heat flux distribution, and a Boussinesq approximation is introduced to represent buoyancy effects. Simulations are performed for Gr = 10^7 , Reτ = 180 and Pr = 0.1. As experimental velocity and temperature profiles are not available in the literature, a preliminary validation of the method employed is performed by the comparison of the global quantities like f and Nu. The time averaged velocity and temperature fields are reported in the paper, together with first order and higher-order statistics. In addition the main turbulent flow features are described through coherent structure eduction methods.