Near-wake flow and thermal characteristics of three side-by-side circular cylinders for large temperature differences using large-eddy simulation

Abstract

The trailing edge of a gas turbine blade contains rows of short circular cylinders which extract the heat from blade, with the help of the coolant. Large temperature differences exist between the incoming coolant and the blade, and its effect on the flow and thermal characteristics need to be understood. To this end, in the present work, non-isothermal flow over three side-by-side circular cylinders is investigated for a Reynolds number of 3900 using large-eddy simulation (LES). The numerical solver used is validated for isothermal flow using reference experimental data. Large temperature differences, ranging from 25∘C to 300∘C, between the incoming flow and the surface of the cylinders are considered and their effect on the flow and thermal characteristics in the near wake region of cylinders are analyzed. The cylinder-surface and wake characteristics are analyzed using instantaneous and mean quantities. The surface characteristics of the cylinders are studied using Nusselt number, wall shear stress, and lift and drag coefficients. The wake characteristics are studied using Reynolds stresses, turbulent heat flux, and turbulence anisotropy invariant maps. Phase-averaging is used to analyze the unsteady flow and topology of the wake. It is observed that, compared to the middle cylinder the production of turbulence and diffusion of heat is higher behind the two outer cylinders, and their location remains stationed independent of the time. Convection and diffusion of heat takes place along the free shear layer of the wake of the middle cylinder. The vortex shedding behind the cylinders are noted to have multiple frequencies. Further, the vortices shed by the outer cylinders contain more energy and at higher-frequencies when compared to those shed by the middle cylinder.