Numerical study of impeller-driven von Karman flows via a volume penalization method

Abstract: The von Karman flow apparatus produces a highly turbulent flow inside a cylinder vessel driven by two counter-rotating impellers. Over more than two decades, this experiment has become a very classic turbulence tool, studied for a wide range of physical systems by many groups, with incompressible flow, compressible flow, for magnetohydrodynamics and dynamo studies inside liquid metal, for particle tracking purposes, and recently with turbulent super-fluid helium. We present a direct numerical simulation (DNS) version the von Karman flow, forced by two rotating impellers. The cylinder geometry and the rotating objects are modelled via a penalization method and implemented in a massive parallel pseudo-spectral Navier-Stokes solver. We choose a special configuration (TM28) of the impellers to be able to compare with set of water experiments well documented. But our good comparison results implied, that our numerical modelling could also be applied to many physical systems and configurations driven by the von Karman flow. The decomposition into poloidal, toroidal components and the mean velocity fields from our simulations are in agreement with experimental results. We analyzed also the flow structure close to the impeller blades and found different vortex topologies.