Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations.

• LES study of heated tandem cylinders at sub-critical Re number for a range of gap ratios (1.0 ≤ L / D ≤ 5.0) are investigated (in increments of 0.25) to study the flow physics and heat transfer. • Based on the gap ratios three distinct flow regimes are reported and discussed: Extended body regime, Shear layer reattachment regime and Co-shedding regime. • Two different Prandtl numbers are investigated to see their effects on the Nusselt numbers. • Flow patterns, lift, drag, pressure coefficients along with Strouhal and Nusselt numbers are presented and discussed for all gap ratios. This study analyses the heat transfer and flow characteristics of cross-flow over two heated infinite cylinders in a tandem (in-line) configuration. Non-isothermal Large Eddy Simulations (LES) using the dynamic Smagorinsky model were conducted at a fixed Reynolds number of 3 , 000 (based on the free stream velocity and the cylinder diameter). A range of cylinder gap ratios (1.0 ≤ L / D ≤ 5.0) was investigated (in increments of 0.25) with two different Prandtl numbers Pr = 0.1 and 1.0. Results show that the flow structures vary according to the order of the patterns: (i) Extended body regime: without attachment for low L / D (1.0 - 1.25) where cylinders behave as a single bluff body with top–bottom vortex shedding, (ii) Shear layer reattachment regime: with reattachment for moderate L / D (1.5 - 3.75) where the detached shear layer from the upstream cylinder reattaches to the downstream cylinder, and (iii) Co-shedding regime: for high gap ratios (3.75 ≤ L / D ≤ 5.0) a phenomenon called "jumping", where the two cylinders behave as isolated bluff bodies. Furthermore, it was observed that the average Nusselt number of both cylinders experience a drastic variation at a critical spacing ratio (between 3.75 ≤ L / D ≤ 4.0). For L / D ≤ 3.0 , the average Nusselt number of the upstream cylinder was found to be higher than that of the downstream one. However, for spacing ratios L / D > 3.0 , the average Nusselt number was similar for both cylinders. For the downstream cylinder, the maximum Nusselt number was located at the separation angle and was found to be independent of the spacing ratio. [ABSTRACT FROM AUTHOR]