Effects of flow structures on turbulence statistics of Taylor-Couette flow in the torque transition state

摘要

Direct numerical simulations of Taylor-Couette flow from Re = 8000 to 25 000 have been conducted to investigate changes of turbulence statistics in the transition of the Reynolds number dependency of the mean torque near Re = 10 000. The velocity fluctuations are decomposed into contributions of the Taylor vortex and remaining turbulent fluctuations. Significant Reynolds number dependencies of these components are observed in the Reynolds stress and the transmission of the mean torque. The contributions of Taylor vortex and turbulent components in the net amount of mean torque are evaluated. The Taylor vortex component is overtaken by the turbulent counterpart around Re = 15 000 when they are defined as a sum of the low axial wave number components of the azimuthally averaged velocity and the remnants. The results show that the torque transition can be explained by the competition between the contributions of Taylor vortex and near wall turbulence.