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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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Visualization of superfluid helium flows in the proximity of boundaries
Hrubcová, Petra ; La Mantia, Marco (advisor) ; Jackson, Martin James (referee)
The investigation of superfluid helium (He II) flows is an active and challenging research field. Progress in our phenomenological understanding of the underlying physics has been achieved in recent years by employing flow visualization techniques that allow following the motion of relatively small particles suspended in the fluid. The flow-induced particle behaviour is studied in the case of thermal counterflow - the most common type of He II flow - close to the flow source, where a significant vorticity enhancement is observed. The work aim is therefore to give a significant contribution to the emerging line of scientific enquiry dedicated to the study of wall-bounded quantum flows.
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Experimental and numerical investigation of quantum turbulence in He II
Varga, Emil ; Skrbek, Ladislav (advisor) ; Golov, Andrei (referee) ; Skyba, Peter (referee)
Superfluid 4 He (He II) is a quantum liquid whose flow is strongly affected by quantum mechanical effects. This thesis presents experimental and numerical studies of turbulent flows in He II - quantum turbulence. Experimentally, quan- tum turbulence is investigated in thermal counterflow, pure superflow and coflow using second sound attenuation, precision local thermometry and by visualisa- tion of helium excimer molecules. The steady state and decay of the vortex line density in pure superflow and counterflow is studied and the universal quasi clas- sical decay is characterised by measurements of the effective kinematic viscosity. General dynamical behaviour is studied in detail in unsteady thermal counter- flow, with various theoretical models tested. A new model where the mean tangle curvature is dependent on the vortex line density is proposed. Temperature de- pendence and enhancement of intermittency in quasi-classical flow in the wake of a moving grid is found using visualisation. Numerically, the interaction of the tangle of quantized vortices with solid tracers is investigated, where a back reaction of the seeding particles on the tangle is identified and its relevance to visualisation experiments is discussed. Additionally, an interesting and as-yet overlooked spherical counterflow is...
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Mathematical modelling of selected problems in cryogenic fluid mechanics
Hodic, Jan ; La Mantia, Marco (advisor) ; Kreml, Ondřej (referee)
The dynamics of low-temperature fluids, such as superfluid helium 4, is an open scientific problem. The experimental study of similarities and differences between quantum (superfluid) and classical (viscous) flows is specifically an active research field, which already led to significant progress in our phenomenological understanding of the underlying physics. It also revealed that a comprehensive theoretical description is still missing, as, for example, in the case of the observed behaviour of moving bodies in quantum flows. The work aim is to derive the existence theory for the weak ort he strong solution of a relevant system of equations based on the Landau model of superfluid helium 4 and appropriate properties of the solution.
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Quantum turbulence in superfluid helium studied by particle tracking velocimetry visualization technique
Duda, Daniel ; Skrbek, Ladislav (advisor) ; Chára, Zdeněk (referee) ; Skyba, Peter (referee)
❚✐t❧❡✿ ◗✉❛♥t✉♠ t✉r❜✉❧❡♥❝❡ ✐♥ s✉♣❡r✢✉✐❞ ❤❡❧✐✉♠ st✉❞✐❡❞ ❜② ♣❛rt✐❝❧❡ tr❛❝❦✐♥❣ ✈❡❧♦❝✐♠❡tr② ✈✐s✉❛❧✐③❛t✐♦♥ t❡❝❤♥✐q✉❡ ❆✉t❤♦r✿ ❘◆❉r✳ ❉❛♥✐❡❧ ❉✉❞❛ ❉❡♣❛rt♠❡♥t✿ ❉❡♣❛rt♠❡♥t ♦❢ ▲♦✇ ❚❡♠♣❡r❛t✉r❡ P❤②s✐❝s ❙✉♣❡r✈✐s♦r✿ ♣r♦❢✳ ❘◆❉r✳ ▲❛❞✐s❧❛✈ ❙❦r❜❡❦✱ ❉r❙❝✳ ❆❜str❛❝t✿ ❚❤❡ P❛rt✐❝❧❡ ❚r❛❝❦✐♥❣ ❱❡❧♦❝✐♠❡tr② ✈✐s✉❛❧✐③❛t✐♦♥ t❡❝❤♥✐q✉❡ ✉s✐♥❣ ♠✐❝✲ r♦♠❡t❡r s✐③❡ s♦❧✐❞ ❞❡✉t❡r✐✉♠ ♣❛rt✐❝❧❡s ❛s tr❛❝❡rs ❤❛s ❜❡❡♥ ❛♣♣❧✐❡❞ t♦ st✉❞② ♦s❝✐❧✲ ❧❛t♦r② ✢♦✇s ♦❢ ❍❡ ■■✱ ✇❤✐❝❤ ✐s ❛ q✉❛♥t✉♠ ✢✉✐❞ ✇✐t❤ q✉❛♥t✐③❡❞ ✈♦rt✐❝✐t②✱ ❛s ✇❡❧❧ ❛s ✢♦✇s ♦❢ ❍❡ ■✱ ✇❤✐❝❤ ✐s ❛ ❝❧❛ss✐❝❛❧ ✈✐s❝♦✉s ❧✐q✉✐❞✱ ❢♦❝✉s✐♥❣ ♦♥ t❤❡ s✐♠✐❧❛r✐t✐❡s ❛♥❞ ❞✐✛❡r❡♥❝❡s ❜❡t✇❡❡♥ t❤❡ q✉❛♥t✉♠ ❛♥❞ ❝❧❛ss✐❝❛❧ ✢♦✇s✳ ❚❤r❡❡ ❡①♣❡r✐♠❡♥ts ❛r❡ ❞❡s❝r✐❜❡❞✿ t❤❡ ✢♦✇ ♣❛st ❛ ❧❛r❣❡✲❛♠♣❧✐t✉❞❡ ❧♦✇✲❢r❡q✉❡♥❝② ♦s❝✐❧❧❛t✐♥❣ ♦❜st❛❝❧❡ ✐♥ t❤❡ ❢♦r♠ ♦❢ ❛ ♣r✐s♠❀ t❤❡ st❡❛❞② str❡❛♠✐♥❣ ✢♦✇ ❞✉❡ t♦ ❛ s♠❛❧❧✲❛♠♣❧✐t✉❞❡ ❧❛r❣❡✲ ❢r❡q✉❡♥❝② ♦s❝✐❧❧❛t✐♥❣ q✉❛rt③ t✉♥✐♥❣ ❢♦r❦ ✲ ❛ ✇✐❞❡❧② ✉s❡❞ t♦♦❧ t♦ st✉❞② q✉❛♥t✉♠ t✉r❜✉❧❡♥❝❡❀ ❛♥❞ t❤❡ ♣r♦❞✉❝t✐♦♥ ♦❢ ❝❛✈✐t❛t✐♦♥ ✐♥ t❤❡ ✈✐❝✐♥✐t② ♦❢ ❛ ❢❛st✲♦s❝✐❧❧❛t✐♥❣ t✉♥✐♥❣ ❢♦r❦✳ ❚❤❡ ♠❛✐♥ ♦✉t❝♦♠❡ ✐s t❤❡ ♦❜s❡r✈❛t✐♦♥ t❤❛t t❤❡s❡ ✢♦✇s ❛r❡ s✐♠✐❧❛r ✐♥ ❍❡ ■ ❛♥❞ ✐♥ ❍❡ ■■ ❛t ❧❛r❣❡ ❧❡♥❣t❤✲s❝❛❧❡s✱ ✇❤❡r❡❛s ❛t s♠❛❧❧ s❝❛❧❡s✱ t❤❡② ❡①❤✐❜✐t t♦t❛❧❧② ❞✐✛❡r❡♥t st❛t✐st✐❝❛❧ ♣r♦♣❡rt✐❡s✳ ▼♦r❡♦✈❡r✱ ✐♥ ❍❡ ■■✱ t❤❡s❡ s♠❛❧❧ s❝❛❧❡ st❛✲ t✐st✐❝❛❧ ♣r♦♣❡rt✐❡s ❛r❡ ✉♥✐✈❡rs❛❧ ✐♥ t❤❛t t❤❡② ❞♦ ♥♦t ❞❡♣❡♥❞ ♦♥ t❤❡ t②♣❡ ♦❢ t❤❡ ✐♠♣♦s❡❞ ♠❡❛♥ ✢♦✇ ♦❢ t❤❡ s✉♣❡r✢✉✐❞ ❛♥❞ ♥♦r♠❛❧...
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Investigation of quantum turbulence using microresonators
Midlik, Šimon ; Schmoranzer, David (advisor) ; Kohout, Jaroslav (referee)
The principal aim of this Thesis is the construction of a cryogenic setup for the investigation of quantum turbulence in superfluid helium (He II) using microresonators and a to perform a study of the transition to turbulence in oscillatory flow of He II in the temperature range from 2.170 K down to 1.293 K. We have designed and constructed a setup consisting of a superconducting vibrating microwire and a so-called fountain pump, and, after initial testing and characterization, used it to probe the instabilities occurring in the flow of He II. Specifically, we were interested in the origin of the instabilities in the flow around the microwire and in the question whether they originate mostly from classical-like flow of the normal component, as is often the case with the well-known tuning forks, or whether they are related to the generation of quantized vortices in the superfluid component of He II. To distinguish between these two types of instabilities, we have derived from the Navier-Stokes equations scaling laws related to drag forces in classical oscillatory flow, which we have applied to the normal component of superfluid helium. This also enabled us to verify the validity of the high-frequency limit of oscillatory flow for the case of the microwire. Finally, we have examined the capability of the...
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Visualization of particle motions in superfluid helium flows
Švančara, Patrik ; La Mantia, Marco (advisor) ; Chagovets, Tim (referee)
Flows of normal and superfluid 4 He (He I and He II, respectively) are investigated experimentally. Relatively small particles of solid hydrogen and deuterium are suspended in the experimental volume and their motions are tracked in both mechanically and thermally driven flows. A statistical study of the particle velocity and velocity increment distributions is performed at scales smaller and larger than the mean distance between quantized vortices, the quantum length scale of the investigated flows. We show that, at small scales, the observed particle dynamics in He II is greatly influenced by that of quantized vortices. We, additionally, report that this behavior is independent of the imposed large-scale flow. Instead, at large scales, we observe that particle motions are quasiclassical, that is, very similar to those reported to occur in turbulent flows of viscous fluids. The study reinforces therefore the idea of close similarity between viscous flows and large-scale (mechanically-driven) flows of He II, and simultaneously highlights the small-scale differences due to the presence of quantized vortices in He II.
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Mathematical modelling of selected problems in cryogenic fluid mechanics
Hodic, Jan ; La Mantia, Marco (advisor) ; Schmoranzer, David (referee)
The dynamics of low-temperature fluids, such as superfluid helium 4, is an open scientific problem. The experimental study of similarities and differences between quantum (superfluid) and classical (viscous) flows is specifically an active research field, which already led to significant progress in our phenomenological understanding of the underlying physics. It also revealed that a comprehensive theoretical description is still missing, as, for example, in the case of the observed behaviour of moving bodies in quantum flows. The work aim is to derive the existence theory for the weak solution of a relevant system of equations based on the Landau model of superfluid helium 4 and appropriate numerical schemes to solve these equations.
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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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Visualization of liquid Helium flows generated by an oscillating rectangular cylinder
Švančara, Patrik ; La Mantia, Marco (advisor) ; Jackson, Martin James (referee)
For the first time, a cylinder of rectangular cross section, performing quasi-harmonic oscillations in liquid helium, was employed for the experimental study of the dynamics of macroscopic vortex structures shed at the sharp edges of the obstacle. The flow of liquid helium was visualized by the motion of small, solidified deuterium particles, dispersed in the experimental cell and illuminated by a thin laser sheet. Experiments in He I, a classical viscous fluid, and He II, a fluid displaying superfluidity, showed, at low frequencies of the oscillating body, a significant difference in the flow, possibly due to the much larger heat conductivity of He I, compared to He I. At large frequencies, the flows appeared instead to be similar, which agrees with the current understanding of quantum flows, at large enough length scales. Powered by TCPDF (www.tcpdf.org)
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