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Abstract: The critical velocity v c for the onset of quantum turbulence in oscillatoryflows of superfluid helium is universal and scales as v c \sim\sqrt{\kappa\omega}, where \kappa is the circulation quantum and \omega is theoscillation frequency. This result can be derived from a general argument basedon the -superfluid Reynolds number-. Only the numerical prefactor may dependsomewhat on the geometry of the oscillating object because the flow velocity atthe surface of the object may differ from the velocity amplitude of the body. Amore detailed analysis derived from the dynamics of the turbulent state givesv c \approx \sqrt{8\kappa\omega-\beta}, where \beta \sim 1 depends on themutual friction parameters. This universality is compared with the recentlydiscovered universality of classical oscillatory flows. We also discuss theeffect of remanent vorticity on the onset of quantum turbulence. Finally, byemploying the -superfluid Reynolds number- again, we argue how v c changes whenthe steady case \omega = 0 is approached. In that case v c scales as \kappa-R,where R is the size of the object.



Author: R. Hänninen, W. Schoepe

Source: https://arxiv.org/



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