Large-eddy simulations of turbulent flow in a rotating square duct

The turbulent flow at low Reynolds numbers in a rotating straight square du ct was simulated using the large-eddy simulation technique. The rotation ax is is parallel to two opposite walls of the duct, and the pressure-driven f low is assumed to be fully developed, isothermal and incompressible. The Re ynolds number based on the friction velocity (Re-tau=300) was kept constant in the range of the rotational numbers studied (0 less than or equal to Ro (tau)less than or equal to 1.5) Computations were carried out using a secon d-order finite volume code with a localized one-equation dynamic subgrid sc ale model. Simulations of rotating channel flows were initially carried out and were seen to be in agreement with experiments and direct numerical sim ulations reported in the literature. The study of the flow in a rotating sq uare duct revealed the influence of the Coriolis force on the spatial distr ibution of the average velocity fields and Reynolds stresses. At low rotati on rates, turbulence-driven secondary flows developed near the corners conv ect the rotation-generated cross-stream currents. At moderate and high rota tion rates, the mean secondary flow structure consists essentially of two l arge counter-rotating cells convecting low/high momentum fluid from the sta ble/unstable side to the unstable/stable side. Inspection of the terms of t he transport equations of the average axial velocity and vorticity componen ts shows the mechanisms responsible for the changes in the average flow str ucture. Spatial distributions of the Reynolds stresses are mainly influence d by the changes that rotation induces in the main strain rates. It has bee n found that, globally, at the low Reynolds number studied, rotation tends to significantly reduce the overall turbulence level of the flow. (C) 2000 American Institute of Physics. [S1070-6631(00)51011-3].