Sub-Kolmogorov-scale fluctuations in wall-bounded hydrodynamic and magnetohydrodynamic shear flows
|Principal Investigator(s)||Dr. Thomas Boeck|
The interaction of turbulence and mean shear is an essential feature of many turbulent flows in nature and technology. Many aspects of shear flow turbulence have been studied in experiments and simulations, but on a fundamental level the understanding is far from complete. While numerical simulations cannot compete with experiments in terms of Reynolds number, they can accurately resolve turbulent high-amplitude fluctuations at the smallest scales of the flow. In simulations of homogeneous isotropic turbulence, such a statistical analysis of velocity gradients has recently received significant attention as it appears to be directly linked to the intermittency in the inertial cascade range and to the fundametal issue of universality of turbulence. This approach requires grid spacings below the Kolmogorov dissipation scale and preferably a spectral numerical method for the accurate computation of gradients. In this proposal, we want to extend these analyses to shear turbulence in a channel, where the properties of the flow depend on the wall-normal coordinate. In addition, we wish to examine the effect of a homogeneous, wallnormal magnetic field on the smallest scales. The magnetic damping of turbulence by the induced currents introduces a strong anisotropy of gradients, which should become particularly significant in the dissipation range. The central question is if the small-scale turbulence is affected by shear and magnetic field. Our planned studies require a non-magnetic and a magnetohydrodynamic channel flow simulation with a pseudospectral Fourier-Chebyshev method at resolutions beyond 10243 grid points.