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We present measurements of the damping experienced by custom-made quartz tuning forks submerged in 3He covering frequencies from 20 kHz to 600 kHz. Measurements were conducted in the bulk of normal liquid 3He at temperatures from 1.5 K down to 12 mK and in superfluid 3He-B well below the critical temperature. The presented results complement earlier work on tuning fork damping in 3He, removing possible ambiguities associated with acoustic emission within partially enclosed volumes and extend the probed range of frequencies, leading to a clearly established frequency dependence of the acoustic losses. Our results validate existing models of damping and point toward the same mechanism of wave emission of first sound in normal 3He and liquid 4He and zero sound in superfluid 3He. We observe a steep frequency dependence of the damping ≈ f5.5, which starts to dominate around 100 kHz and restricts the use of tuning forks as efficient sensors in quantum fluids. The acoustic emission model can predict the limiting frequencies for various devices, including micro-electromechanical and nano-electromechanical structures developed for quantum turbulence and single vortex dynamics research.

We present measurements of the damping experienced by custom-made quartz tuning forks submerged in 3He covering frequencies from 20 kHz to 600 kHz. Measurements were conducted in the bulk of normal liquid 3He at temperatures from 1.5 K down to 12 mK and in superfluid 3He-B well below the critical temperature. The presented results complement earlier work on tuning fork damping in 3He, removing possible ambiguities associated with acoustic emission within partially enclosed volumes and extend the probed range of frequencies, leading to a clearly established frequency dependence of the acoustic losses. Our results validate existing models of damping and point toward the same mechanism of wave emission of first sound in normal 3He and liquid 4He and zero sound in superfluid 3He. We observe a steep frequency dependence of the damping ≈ f5.5, which starts to dominate around 100 kHz and restricts the use of tuning forks as efficient sensors in quantum fluids. The acoustic emission model can predict the limiting frequencies for various devices, including micro-electromechanical and nano-electromechanical structures developed for quantum turbulence and single vortex dynamics research.

We present a unified analysis of the drag forces acting on oscillating bodies submerged in superfluid helium such as a vibrating wire resonator, tuning forks, a double-paddle oscillator, and a torsionally oscillating disk. We find that for high-Stokes-number oscillatory flows, the drag force originating from the normal component of superfluid helium exhibits a clearly defined universal scaling. Following classical fluid dynamics, we derive the universal scaling law and define relevant dimensionless parameters such as the Donnelly number. We verify this scaling experimentally using all of our oscillators in superfluid 4 He and validate the results by direct comparison with classical fluids. We use this approach to illustrate the transition from laminar to turbulent drag regime in superfluid oscillatory flows and compare the critical velocities associated to the production of quantized vortices in the superfluid component with the critical velocities for the classical instabilities occurring in the normal component. We show that depending on the temperature and geometry of the flow, either type of instability may occur first and we demonstrate their crossover due to the temperature dependence of the viscosity of the normal fluid. Our results have direct bearing on present investigations of superfluids using nanomechanical devices [Bradley et al., Sci. Rep. 7, 4876 (2017)].

We present a unified analysis of the drag forces acting on oscillating bodies submerged in superfluid helium such as a vibrating wire resonator, tuning forks, a double-paddle oscillator, and a torsionally oscillating disk. We find that for high-Stokes-number oscillatory flows, the drag force originating from the normal component of superfluid helium exhibits a clearly defined universal scaling. Following classical fluid dynamics, we derive the universal scaling law and define relevant dimensionless parameters such as the Donnelly number. We verify this scaling experimentally using all of our oscillators in superfluid 4 He and validate the results by direct comparison with classical fluids. We use this approach to illustrate the transition from laminar to turbulent drag regime in superfluid oscillatory flows and compare the critical velocities associated to the production of quantized vortices in the superfluid component with the critical velocities for the classical instabilities occurring in the normal component. We show that depending on the temperature and geometry of the flow, either type of instability may occur first and we demonstrate their crossover due to the temperature dependence of the viscosity of the normal fluid. Our results have direct bearing on present investigations of superfluids using nanomechanical devices [Bradley et al., Sci. Rep. 7, 4876 (2017)].

"JOHN ADAMS SCHOOL ACTIVITIES will be announced in this new sign purchased and installed by members of the John Adams Key Club. Accepting the gift for the high school is Principal Michael P. Effron (right). Installing the sign are Richard Oleska of 11308 Clarebird Dr., club president (left); Don Brienik, 9814 Dunlop Ave.; Ted Calabrese, 11209 East Blvd.; Bob Dzama, 3443 E. 113th St. and Robert A. Midlik, club adviser and a biology teacher at Adams." - photo verso., A13879