Fizika Nizkikh Temperatur: Volume 46, Number 10 (October 2020), p. 1147-1154 ( to contents , go back )
The critical velocity of transition to turbulence in 3He –4He liquid solutions
V. A. Vrakina1, E. Ya. Rudavskii1, S. S. Sokolov1, V. K. Chagovets1,2, G. A. Sheshin1, and T. V. Chagovets3
1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine Kharkiv 61103, Ukraine
2V.N. Karazin Kharkiv National University, 4 Svoboda Sq., Kharkiv 61022, Ukraine
3Institute of Physics of the Czech Academy of Sciences, Prague 18221, Czech Republic
Received May 19, 2020, published online August 21, 2020
The transition between laminar and turbulent flows around a quartz tuning fork oscillating in superfluid 4He and concentrated solutions (5 and 15% 3He in 4He) with frequency ω in the temperature range 0.3–2.3 K was studied. The temperature dependences of the transition critical velocity νcr amplitude were obtained and it was shown that the ratio νcr~√with one fitting parameter can be used for describing these dependences in concentrated solutions of 3He in 4He with viscosity η and density ρ, but this ratio does not fulfill for the temperature dependence of vcr of pure 4He in whole studied temperature range. It was also shown that in concentrated solutions 3He–4He, in a contrary to pure 4He, the temperature almost does not affect the value of the flow resistance coefficient in both laminar and turbulent modes. There are constructed the concentration dependences of the flow resistance coefficient in the laminar mode normalized to the effective cross-section area of the oscillating body in the 0.5–1 K temperature range. The calculated dependences showed that in the region of low solution concentrations, with x3 < 1 % of 3Не, the normalized coefficient weakly depends on the concentration of 3He and can be qualitatively described by the ratio λ / S ~√ . In the concentration range with x3 > 1 % of 3Не, the coefficient rises sharply and the reason for this increase is currently not understood. In general, the results of the study show that an increase in the concentration of 3He in a solution leads to an increase in its stability with respect to the occurrence of turbulence with an increase in the excitation force of a quartz tuning fork.
Key words: superfluid solutions 3Не–4Не, quartz tuning fork, turbulence, critical velocity.