title: Transition from laminar to turbulent drag in flow due to a vibrating quartz fork.
abstract: Flow due to a commercially available vibrating quartz fork is studied in gaseous helium, He I and He II, over a wide range of temperatures and pressures. On increasing the driving force applied to the fork, the drag changes in character from laminar (characterized by a linear drive vs velocity dependence) to turbulent (characterized by a quadratic drive vs velocity dependence). We characterize this transition by a critical Reynolds number Recrdelta=Ucrdelta/nu, where Ucr is the critical velocity, nu stands for the kinematic viscosity, delta=sqrt[2nu/omega] is the viscous penetration depth, and omega is the angular frequency of oscillations. We have experimentally verified that the corresponding scaling Ucr proportional, sqrt[nuomega] holds in a classical viscous fluid over two decades of nu.
authors.affiliation: Joint Low Temperature Laboratory, Institute of Physics ASCR and Faculty of Mathematics and Physics, Charles University, V Holesovickách 2, 180 00 Prague, Czech Republic.
authors.forename: M
authors.initials: M
authors.lastname: Blazková
authors.forename: D
authors.initials: D
authors.lastname: Schmoranzer
authors.forename: L
authors.initials: L
authors.lastname: Skrbek