Direct Numerical Simulation Of Turbulent Elliptical Pipe Flow Under System Rotation About The Major Axis

The effect of Coriolis forces on the turbulent flow in an elliptical pipe subjected to spanwise rotation about the major axis has been studied using direct numerical simulations (DNS). In response to the system rotation, large-scale secondary flows appear in the cross-stream plane as a pair of counterrotating vortices, which significantly impact the turbulence statistics and structures of the flow. To capture the most energetic turbulent eddy motions in the streamwise direction, the pipe length has been extended to L-z = 20 pi b (here, b is the minor semiaxis of the elliptical pipe), which is the longest in the current literature for the study of elliptical pipe flows. Laminarization occurs on the suction side of the flow and propagates toward the pressure side as the speed of the system rotation increases. The system rotation imposed radically alters the budget balance of Reynolds stresses through its effects on the mean and turbulent flow fields and through the Coriolis term. At a moderate rotation number, the Coriolis term starts to dominate the energy transfer from < w'w'> to < v'v'>, and also acts on < v'w'> as an additional source term. This mechanism far surpasses the role of the pressure-strain term, which undergoes a significant reduction in response to the system rotation. The characteristics of the turbulence field is investigated in both physical and spectral spaces through analyses of the first- and second-order statistical moments, as well as the budget balance of the Reynolds stress transport equation and coherent flow structures.