Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W15: Instabilities & Turbulence |
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Sponsoring Units: DFD Chair: James Brasseur, Pennsylvania State University Room: 304 |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W15.00001: Linear stability analysis of two phase stratified one dimensional Poiseuille flow with surfactant at the interface, in a channel Ashutosh Singh, Subramaniam Pushpavanam Linear stability analysis of one dimensional Poiseuille flow of two superposed fluids with surfactant at the interface is considered in a channel . Three dimensional disturbance is considered for arriving at the Orr-Sommerfeld equations for both the fluids. The mathematical formulation yields a generalized eigen value problem Ax$=$cBx, which is solved by numerically by spectral collocation technique. Gaussian elimination is employed to recast the eigen value problem as A'x'$=$cB'x' in order to get rid of the zero rows in B as explained by Boomkamp. Dispersion curves are plotted for different Reynolds numbers in order to distinguish between interfacial and shear modes for both the cases ;with and without surfactant at the interface. The role of surfactant in stabilization is investigated and the results for pure interface case are compared with that of Yiantsios and Higgins. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W15.00002: Buoyancy Driven Mixing Induced by Volumetric Energy Deposition Adam J. Wachtor, Veronika Mocko, Farzaneh F. Jebrail, Malcolm J. Andrews, Robert A. Gore A two fluid, buoyancy driven mixing experiment, which transitions from a Rayleigh-Taylor stable configuration to a Rayleigh-Taylor unstable configuration via preferential heating obtained with microwaves, is presented. The experiment is initiated with a light, non-polar fluid at rest atop a heavier, more polar fluid. Microwave energy causes rotation of the polar molecules in the heavier fluid, and the density of the bottom fluid begins to drop due to thermal expansion. As heating of the bottom fluid continues, the system passes through the neutral stability point and buoyancy driven mixing ensues. Challenges for designing an experimental facility, and data collection limitations, for this investigation are discussed. Experimental and numerical predictions of the neutral stability point, and onset of buoyancy driven mixing, are compared, and differences with classical Rayleigh-Taylor driven turbulence are discussed. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W15.00003: Instability of displacement of Oldroyd-B fluid by air in a Hele-Shaw cell Prabir Daripa We study the displacement of an Oldroyd-B fluid in a Hele-Shaw cell when driven by air. In particular, we explicitly obtain an analytical expression for the growth rate of instability which depends on the relaxation and retardation (time) constants, denoted by $\lambda$, and $\lambda_1$ respectively, appearing in the Oldroyd-B constitutive relations. When these two constants are zero, we recover the classical Saffman-Taylor result for a Newtonian liquid displaced by air. Our results show that this displacement process is more unstable than the case when a Newtonian fluid is displaced by air. The analytical results are plotted and compared with numerical results on this unstable displacement process available in the literature. The agreement is found to be excellent. In particular, results show that the non-Newtonian case (i.e., Oldroyd-B) is more unstable than the Newtonian case. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W15.00004: The Transition in Structure of the Atmospheric Boundary Layer from Neutral with Surface Heating James Brasseur, Balaji Jayaraman The scales, strengths and detailed structure of atmospheric boundary layer (ABL) turbulence are strongly dependent on the relative contributions of buoyancy-driven vertical motions from surface heating and shear driven motions from geostrophic winds at the mesoscale, as characterized by the global stability state parameter --$z_{i}$/$L$. In the shear-dominant neutral limit, the ABL is characterized by streamwise-elongated coherent eddies of negative fluctuating horizontal velocity As surface heating is increased, buoyancy drives vertical fluctuations strongly correlated with shear-driven motions that eventually organize to generate streamwise rolls that couple upper with lower boundary layer. We use large-eddy simulation (LES) to study this transition between ``near neutral'' and ``moderately convective'' by quantifying correlations and integral scales as a function of -$z_{i}$/$L. $The interactions between outer and the surface layer eddies generate surprising turbulence dynamics that includes a special transitional stability state with unusually enhanced streamwise coherence. The transitional process includes a critical phenomenon with sudden dramatic change in ABL structure, and high sensitivity in horizontal fluctuations to surface heating at a low --$z_{i}$/$L.$ \textit{Supported by DOE}. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W15.00005: Logarithmic scaling in the longitudinal velocity variance explained by a spectral budget in a neutral and unstable atmosphere Tirtha Banerjee, Gabriel Katul, Scott Salesky, Marcelo Chamecki A logarithmic scaling for the streamwise turbulent intensity $\sigma_u^2/{{u_*}^2}=B_1-A_1\,\ln\left({z}/{\delta}\right)$ was reported across several high Reynolds number laboratory experiments as predicted from Townsend's attached eddy hypothesis, where $u_*$ is the friction velocity and $z$ is the height normalized by the boundary layer thickness $\delta$. A phenomenological explanation for the origin of this log-law in the intermediate region is provided here based on a solution to a spectral budget where the production and energy transfer terms are modeled. The solution to this spectral budget predicts $A_1=C_o/{\kappa^{2/3}}$ and $B_1=(3/2) A_1$, where $C_o$ and $\kappa$ are the Kolmogorov and von K\'arm\'an constants. The spectral budget approach is then extended to explore the scaling behavior of $\sigma_u/{{u_*}}$ in the unstably stratified atmosphere. It is demonstrated with support from recent datasets that $\sigma_u/{{u_*}}$ does not only depend on $\delta/L$ but also depends on the atmospheric stability parameter $\zeta=z/L$. Thus, the proposed spectral budget shows how Townsend's attached eddy hypothesis, the $k^{-1}$ spectral law in low wavenumbers and the similarity arguments for a stratified atmosphere are all interconnected. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W15.00006: Study of Turbulence Statistics in Large-Eddy Simulation of Ocean Current Turbine Environments Spencer Alexander, Peter Hamlington As ocean current turbines move from the design stage into production and installation, a better understanding of both oceanic turbulent flows and localized loading is needed by researchers and members of industry. The use of realistic ocean turbulence in Large-Eddy Simulations (LES) of ocean turbines is essential in obtaining realistic ocean turbine loading and characteristics. In this study, an ocean current turbine environment is simulated using the National Center for Atmospheric Research (NCAR) LES model. The inflow and boundary conditions are designed to represent conditions during an observational campaign at Admiralty Inlet in Puget Sound (Thomson, et al. 2012). Comparisons are first made between the LES simulation results and available measurements from the Admiralty Inlet, and further measures are then presented from the LES results, including vertical profiles of Reynolds stresses, anisotropy, turbulent loading, and two point correlations. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W15.00007: Local Dissipation Scales in Homogeneous Sheared Turbulence Ryan King, Peter Hamlington The effects of shear on local dissipation scales in turbulent flows have been examined using direct numerical simulations (DNS) of homogeneously sheared turbulence. In the classical theory of turbulence it is assumed that there is a universal equilibrium range and effects of a large-scale shear are lost at small spatial scales. Recent numerical and experimental studies have shown that large-scale anisotropy can remain significant at small scales. Furthermore, the local dissipation scale distributions have been found to depend on wall distance in turbulent pipe and channel flows and on measurement location in backward-facing step flows. The exact influence of mean shear and large-scale flow properties in these flows remains unclear due to the presence of confounding wall effects or flow separation. We use DNS of homogeneously sheared turbulence to determine the dependence of local dissipation scales on the shear and Reynolds number in the absence of these wall or flow separation effects. This study also tests the assumption that a universal equilibrium range exists and that small-scale behavior is independent of large-scale flow properties. Finally, comparisons are made with prior studies of local dissipation scales in both homogeneous, isotropic and wall-bounded shear flows. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W15.00008: Suppressing Turbulence and Enhancing the Liquid Suspension Flow in Pipeline with Electromagnetic Fields G.Q. Gu, R. Tao Flows through pipes are the most common and important transportation of fluids. To enhance the flow output along pipeline, it requires reducing the fluid viscosity and suppressing turbulence simultaneously and effectively. Unfortunately, no method is currently available to accomplish both goals simultaneously. Fore example, heating reduces the fluid viscosity, but makes turbulence worse. Here we show that the symmetry breaking physics provides an efficient solution for this issue. When a strong electromagnetic field is applied in the flow direction in a small section of pipeline, the field polarizes and aggregates the particles suspended inside the base liquid into short chains along the flow direction. Such aggregation breaks the symmetry and makes the fluid viscosity anisotropic. Along the flow direction, the viscosity is significantly reduced; in the directions perpendicular to the flow, the viscosity is substantially increased. The turbulence is thus suppressed as all rotating motions and vertexes are suppressed. Only the flow along the pipeline is enhanced and the outflow is improved. The method is extremely energy efficient since it only aggregates the particles and does not heat the suspensions. Recent field tests on pipeline fully support the theoretical prediction. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W15.00009: Modeling the Effects of Turbulence in Rotating Detonation Engines Colin Towery, Katherine Smith, Peter Hamlington, Marthinus Van Schoor Propulsion systems based on detonation waves, such as rotating and pulsed detonation engines, have the potential to substantially improve the efficiency and power density of gas turbine engines. Numerous technical challenges remain to be solved in such systems, however, including obtaining more efficient injection and mixing of air and fuels, more reliable detonation initiation, and better understanding of the flow in the ejection nozzle. These challenges can be addressed using numerical simulations. Such simulations are enormously challenging, however, since accurate descriptions of highly unsteady turbulent flow fields are required in the presence of combustion, shock waves, fluid-structure interactions, and other complex physical processes. In this study, we performed high-fidelity three dimensional simulations of a rotating detonation engine and examined turbulent flow effects on the operation, performance, and efficiency of the engine. Along with experimental data, these simulations were used to test the accuracy of commonly-used Reynolds averaged and subgrid-scale turbulence models when applied to detonation engines. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W15.00010: Studies in Quantum Plasma Turbulence Cassandra Oduola Turbulence is a phenomenon associated with chaotic and stochastic change in properties. At the quantum level, turbulence can be found in quantum fluids also known as super fluids; a friction free state of matter containing charged particles. Super fluidity has recently been observed at the core of neutron stars. These fluids containing also act as superconductors. Studies have found that the remaining protons in the star's core are also in a superfluid state and because they carry a charge also form a superconductor. This study employs the non-linear Schrodinger coupled with Poisson's equation for three dimensional quantum turbulence simulations. These simulations follow Fermi-Dirac statistics. Research has found evidence of soliton solutions to the non-linear Schrodinger. Solitons are self-reinforcing waves in nature that are also symmetric. Evidence of these solitons has been found in quantum turbulence. In order to verify the existence of solitons in this model, we aim to model solutions to the Non Linear Schrodinger in 1D and to obtain data to verify the these solitons. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W15.00011: Generalized Hasimoto Transform, Binormal Flow and Quantized Vortices Scott A. Strong, Lincoln D. Carr A quantized vortex is a topological object central to the study of quantum liquids. Current models of vortex dynamics are motivated by the nonlinear Schr\"odingier equation and porting techniques from classical vortices. Self induction of classical vorticity ideally localized to a space curve asserts that a curved vortex filament propagates at a speed proportional to its curvature, $|\textbf{v}|\propto\kappa$, in the binormal direction of the Frenet frame, $\hat{\textbf{b}}$. Interestingly, this autonomous dynamic can be mapped into the space of solutions to a cubic focusing nonlinear Schr\"odinger equation, $i\psi_{t}+\psi_{ss}+\frac{1}{2}|\psi|^{2}\psi=0$, where $\psi$ is a plane-wave defined by curvature and torsion of the vortex filament, $\psi=\kappa\exp[i\int ds\tau]$. Using these two results, one can define a vortex configuration, within superfluid helium or a Bose-Einstein condensate, and prescribe a binormal evolution. In general, however, binormal flow depends nonlinearly on local curvature and maps to a class of nonlinear integro-differential Schr\"odinger equations. In this talk we discuss how system size affects higher-order nonlinearity and filament geometry which is applicable to theoretical and numerical investigations of vortex dominated quantum hydrodynamics. [Preview Abstract] |
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