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Steady state and decay of quantum turbulence generated in channel flows and detected by second sound attenuation
Varga, Emil ; Skrbek, Ladislav (advisor) ; Vinen, William Frank (referee)
Steady state and decay of quantum turbulence generated in channel flows and detected by second sound attenuation Bc. Emil Varga Abstract Quantum turbulence is studied in superfluid 4 He under classical flow condi- tions. Turbulence is generated by a flow through a 7 × 7 mm square channel with a flow conditioner either with an additional grid or without it. The flow is generated mechanically by squeezing a stainless steel bellows. Vortex line den- sity is measured by attenuation of second sound in both steady state and decay for a range of temperatures 1.17 - 2.16 K. In the steady state, temperature- independent scaling of the vortex line density with flow velocity of the form L ∝ V 3/2 is observed. In the decay the expected late-time behaviour L ∝ t−3/2 is observed. Explanation for both of these observations is based on a quasi- classical model of quantum turbulence, that allows the extraction of the effective kinematic viscosity νeff, which approximately agree with the values available in the literature. Two models based on counterflow theory are also explored and the effect of inhomogeneous vortex line distribution on the measurement tech- nique is studied.
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Generation and detection of quantum turbulence in He II by second sound
Midlik, Šimon ; Schmoranzer, David (advisor) ; La Mantia, Marco (referee)
We have performed a study of quantum turbulence generated in oscillatory counterflow as a continuation of previous experiments on various channel flows of superfluid helium, in the form of coflow, thermal DC counterflow and pure superflow. We have investigated its development, steady state properties and temporal decay, as well as the effect of the resonant mode used to generate the turbulence at three different temperatures, 1.45 K, 1.65 K and 1.83 K. The attenuation of low amplitude second sound, orientated perpendicularly to the long axis of the resonator, was used to determine the amount of quantized vortices created. One of the main goals of this work was to characterize the critical parameters for the onset of instabilities in oscillatory counterflow and to determine their values. Decay measurements of the vortex line density allowed us to distinguish between Vinen-type and Kolmogorov- type decays of quantum turbulence.
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Generation and detection of quantum turbulence in He II by second sound
Midlik, Šimon ; Schmoranzer, David (advisor) ; La Mantia, Marco (referee)
We have performed a study of quantum turbulence generated in oscillatory counterflow as a continuation of previous experiments on various channel flows of superfluid helium, in the form of coflow, thermal DC counterflow and pure superflow. We have investigated its development, steady state properties and temporal decay, as well as the effect of the resonant mode used to generate the turbulence at three different temperatures, 1.45 K, 1.65 K and 1.83 K. The attenuation of low amplitude second sound, orientated perpendicularly to the long axis of the resonator, was used to determine the amount of quantized vortices created. One of the main goals of this work was to characterize the critical parameters for the onset of instabilities in oscillatory counterflow and to determine their values. Decay measurements of the vortex line density allowed us to distinguish between Vinen-type and Kolmogorov- type decays of quantum turbulence.
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Steady state and decay of quantum turbulence generated in channel flows and detected by second sound attenuation
Varga, Emil ; Skrbek, Ladislav (advisor) ; Vinen, William Frank (referee)
Steady state and decay of quantum turbulence generated in channel flows and detected by second sound attenuation Bc. Emil Varga Abstract Quantum turbulence is studied in superfluid 4 He under classical flow condi- tions. Turbulence is generated by a flow through a 7 × 7 mm square channel with a flow conditioner either with an additional grid or without it. The flow is generated mechanically by squeezing a stainless steel bellows. Vortex line den- sity is measured by attenuation of second sound in both steady state and decay for a range of temperatures 1.17 - 2.16 K. In the steady state, temperature- independent scaling of the vortex line density with flow velocity of the form L ∝ V 3/2 is observed. In the decay the expected late-time behaviour L ∝ t−3/2 is observed. Explanation for both of these observations is based on a quasi- classical model of quantum turbulence, that allows the extraction of the effective kinematic viscosity νeff, which approximately agree with the values available in the literature. Two models based on counterflow theory are also explored and the effect of inhomogeneous vortex line distribution on the measurement tech- nique is studied.
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