Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B08: Superfluids: General |
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Chair: Luminita Danaila, University of Rouen Normandy Room: 212 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B08.00001: Flying in a superfluid: starting flow past an airfoil Seth Musser, Davide Proment, Miguel Onorato, William Irvine We investigate the development of superfluid flow around an airfoil accelerated to a finite velocity from rest. Using both simulations of the Gross-Pitaevskii equation and analytical calculations we find striking similarities to viscous flows: from the production of starting vortices to the convergence of the airfoil circulation onto a quantized version of the classical Kutta-Joukowski circulation. Using a phenomenological argument we predict the number of vortices nucleated by a given foil and find good agreement with numerics. Finally we analyze the lift and drag acting on the airfoil. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B08.00002: Small particle motions in inhomogeneous super fluid turbulence Takumi Maruyama, Shinichiro Waki, Sou Suzuki, Volker Sonnenschein, Hideki Tomita, Yoshiyuki Tsuji, Tetsuo Iguchi Lagrangian trajectories of small particles in a fully developed turbulent state are studied in a rectangular duct. A plate heater is attached on the bottom to generate the thermal counter flow. The bath temperature is changed from $1.9$ K to $2.1$ K, and is controlled within $0.1$ mK. Small particles made of solid hydrogen are visualized by high-speed camera and their trajectories are recorded. Their motions indicate complex features depending not only on bath temperature and heater power, but also on particle size. Particle motions near the wall are different from those at duct center. We report the effect of flow inhomogeneity on the particle motions. Smaller particle tends to be affected by the inhomogeneity than the larger particle sizes. To characterize the particle motions, the Hurst exponent is defined by $|\vec{x}(t+\tau)-\vec{x}(t)| \propto \tau^H$, where $\vec{x}(t)$ denotes the particle position at time $t$. It is found that there is a characteristic time scale $\tau_0$[1]. For small time separation, $\tau \le \tau_0$, the exponent $H$ is small. However, for large time separation, $\tau_0 \ll \tau$, $H$ is nearly $1$. [1] W.Kubo and Y.Tsuji, Journal of Low Temperature Physics, 2019, Volume 196, pp 170–176 [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B08.00003: Quantum turbulence exploration using the Gross-Pitaevskii equation Luminita Danaila, Michikazu Kobayashi, Francky LUDDENS, Corentin Lothode, Philippe PARNAUDEAU, Ionut Danaila, Marc Brachet We solve numerically the Gross-Pitaevskii (GP) equation to simulate the dynamics of Quantum Turbulence (QT) in a periodic box. This intends to model the behaviour of superfluid helium in the low-temperature regime, therefore a viscous-free flow. Simulations are performed with a spectral code solving the GP equation using MPI-OpenMP parallel programming. We assess the effect of different initial conditions on the statistical behaviour of the flow, through both spectra and structure functions. Closures for non-linear energy transfer terms are proposed and validated, mainly based on vortex reconnection mechanism. Analogies and differences between QT and classical turbulence are drawn. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B08.00004: A Laser system for flow field imaging in superfluid helium using He$_{2}$* So Suzuki, Volker Sonnenshein, Takumi Maruyama, Shinichiro Waki, Hideki Tomita, Yoshiyuki Tsuji, Tetsuo Iguchi For visualization of the flow field in superfluid Helium (He II), He$_{2}$* excimer can be traced by using Laser induced fluorescence (LIF). In our group the proposed He$_{2}$* excimer generation method is based on the neutron absorption reaction of naturally abundant $^{3}$He in Helium. Small He$_{2}$* clusters generated by this method are then available for 3D LIF imaging. By applying this method, we already confirmed successful generation of He$_{2}$* excimers using our laser system. In this study, for successful visualization of He$_{2}$* excimer images in superfluid Helium, the required laser parameters, such as f intensity, repetition rate and wavelength were investigated. For systematic characterization of these, an offline system based on a high voltage discharge for excimer generation is being set up to provide a more intense and accessible source of excimers, not requiring the use of a neutron beam. [Preview Abstract] |
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