Modeling rotating and swirling turbulent flows: A perpetual challenge

Several types of rotating and swirling flows for a range of Reynolds numbers and rotation rates or swirl intensities have been studied computationally, aimed at identifying specific features that require special consideration in turbulence modeling. The flows considered include turbulent channel flows subjected to streamwise and spanwise rotation, with stationary and moving boundaries; developing and fully developed flows in axially rotating pipes; and swirling flows in combustor geometries and long pipes. Computations performed with three versions of the second moment closure and two eddy-viscosity models show that the second-moment models are superior, especially when the equations are integrated up to the wall. Such models reproduced the main flow parameters for all flows considered in acceptable agreement with the available experimental data and direct numerical simulations. However, challenges still remain in predicting accurately some specific flow features, such as capturing the transition from a free vortex to solid-body rotation in along straight pipe with a weak swirl, or reproducing the normal stress components in the core region. Also, the so-called (uw) over bar anomaly in fully developed flows with streamwise rotation remains questionable. For rotating flows, the low-Reynolds-number models yield a somewhat premature flow relaminarization at high rotation speeds.