Direct Numerical Simulation Of Turbulent Taylor-Couette Flow

This thesis is dedicated to the study on the turbulent Taylor-Couette (TC) flow through direct numerical simulations(DNS). Specifically, the effects of the Reynolds number (Re), the ratio between the inner and outer cylinder radii, and the counter rotation of the outer cylinder on the large-scale Taylor vortices and in turn the turbulence fluctuations are closely examined. Moreover, the contribution of the Taylor vortices to the turbulence statistics quantitified and discussed. Also, the underlying mechanism of turbulent TC flow relevant to the change in turbulence behavior has been explored.The effects of the Re number on the turbulent TC flow is found that increasing Re leads to an enhanced turbulent flow state. Specifically, for a higher Re the mean flow shear is more intensive at the inner cylinder wall which results in a larger peak value of turbulence intensity that shifts towards the cylinder walls. Moreover, the large-scale Taylor voticies distorted in shape contribute less to the turbulenc statistics. For the higher Re TC flow, the dynamic processes linked to the production, dissipation and redistribution of the turbulence fluctuations become more intensive, in particular the radial fluctuating motions become dominant in redistributing the turbulent kinetic energy.The effects of the radius ratio on the turbulent TC flow is found as follows. In response to the increase of the radius ratio, the random fluctuating motions become to contribute less, in comensurate with an increase of the contributions from the large-scale Taylor vortices to the turbulence statistics. For a small radius ratio, the TC flow is mainly dominated by the random fluctuating motions, and the radial flucutuationg motions contribute a main part of the turbulent kinetic energy. For a large radius ratio, however, the TC flow is dominated by the vertical motion of the Taylor vortices, leads to the flow features similar to those of a turbulent planar Couette flow.The effects of the counter rotation of the outer cylinder wall on the turbulent TC flow is found as follows. For a small counter rotating speed at the outer wall, the large-scale Taylor vortices act as an important role in the production, dissipation and redistribution of turbulent kinetic energy and Reynolds stresses. When increasing the counter rotating speed at the outer wall, the mean flow shear in the wall regions bec- omes to dominate the dynamic processes linked to the turbulence fluctuations, and in the center region the turbulent flow features are determined by the random flucutating motions...