Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session R41: Minisymposium on Turbulence in Honor of John L. Lumley |
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Chair: Nadine Aubry, Northeastern University Room: Sheraton Constitution A |
Tuesday, November 24, 2015 12:50PM - 1:16PM |
R41.00001: John Leask Lumley: In Memoriam Invited Speaker: Sidney Leibovich John Lumley, a major contributor to turbulence research in the last half century, was a complex man of many talents. This talk is a personal reflection on a friendship of long standing. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R41.00002: Fine-scale turbulence induced axial flow and instability of a vortex column Invited Speaker: Fazle Hussain Interaction of fine-scale turbulence with a coherent vortex column and its possible induction of axial flow leading to column instability is studied using direct numerical simulations. Vortex threads form from the fine-scale turbulence due to mean strain of the column and self-advect in the (primarily) axial and radial directions. Self-advection depends on the thread circulation and orientation, and radial advection causes similar threads with opposite circulations to radially separate, resulting in an axial flow. As axial flow increases both with Reynolds number ($\equiv $vortex circulation/viscosity) and in time, instability due to axial flow (indicated by the ratio of maximum azimuthal velocity to maximum axial velocity, or the $q$ criterion) can cause perturbation growth. For the simplified perturbation of two oppositely oriented vortex threads, axial flow is generated and, at sufficient amplitudes, perturbation amplification occurs, possibly leading to instability. [Preview Abstract] |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R41.00003: Reduced order modeling of wall turbulence Invited Speaker: Parviz Moin Modeling turbulent flow near a wall is a pacing item in computational fluid dynamics for aerospace applications and geophysical flows. Gradual progress has been made in statistical modeling of near wall turbulence using the Reynolds averaged equations of motion, an area of research where John Lumley has made numerous seminal contributions. More recently, Lumley and co-workers\footnote{Aubry \textit{et al.}, JFM, \textbf{192}, 1988.} pioneered dynamical systems modeling of near wall turbulence, and demonstrated that the experimentally observed turbulence dynamics can be predicted using low dimensional dynamical systems. The discovery of minimal flow unit\footnote{Jimenez and Moin, JFM, \textbf{225}, 1991.} provides further evidence that the near wall turbulence is amenable to reduced order modeling. The underlying rationale for potential success in using low dimensional dynamical systems theory is based on the fact that the Reynolds number is low in close proximity to the wall. Presumably for the same reason, low dimensional models are expected to be successful in modeling of the laminar/turbulence transition region. This has been shown recently using dynamic mode decomposition.\footnote{Sayadi \textit{et al.}, JFM, \textbf{748}, 2014.} Furthermore, it is shown that the near wall flow structure and statistics in the late and non-linear transition region is strikingly similar to that in higher Reynolds number fully developed turbulence.\footnote{Sayadi \textit{et al.}, JFM, \textbf{724}, 2013.} In this presentation, I will argue that the accumulated evidence suggests that wall modeling for LES using low dimensional dynamical systems is a profitable avenue to pursue. The main challenge would be the numerical integration of such wall models in LES methodology. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R41.00004: POD analysis of turbulent pipe flow Alexander J. Smits, Leo Hellstr\"om, Bharathram Ganapathisubramani Proper Orthogonal Decomposition was introduced into the analysis of turbulent flow by Lumley (1967, 1981). Turbulent flows pose particular challenges for POD analysis because the energy is distributed over a wide range of scales. It has recently been found, however, that POD can be a powerful experimental tool for identifying the largest scales, especially the Large Scale Motions (LSMs) and Very Large Scale Motions (VLSMs) in turbulent pipe flow. It has also been useful, for example, to identify the large-scale motions that dominate the unsteady behavior of the flow downstream of a right-angled bend. Here, we summarize some of these experimental results, and discuss their implications for the understanding of turbulence structure. [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R41.00005: Low dimensional modeling of wall turbulence Invited Speaker: Nadine Aubry In this talk we will review the original low dimensional dynamical model of the wall region of a turbulent boundary layer [Aubry, Holmes, Lumley and Stone, Journal of Fluid Dynamics 192, 1988] and discuss its impact on the field of fluid dynamics. We will also invite a few researchers who would like to make brief comments on the influence Lumley had on their research paths. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R41.00006: John Lumley's Contributions to Turbulence Modeling Invited Speaker: Stephen Pope We recall the contributions that John Lumley made to turbulence modeling in the 1970s and 1980s. In these early days, computer power was feeble by today’s standards, and eddy-viscosity models were prevalent in CFD. Lumley recognized, however, that second-moment closures represent the simplest level at which the physics of turbulent flows can reasonably be represented. This is especially true when the velocity field is coupled to scalar fields through buoyancy, as in the atmosphere and oceans. While Lumley was not the first to propose second-moment closures, he can be credited with establishing the rational approach to constructing such closures. This includes the application of various invariance principles and tensor representation theorems, imposing the constraints imposed by realizability, and of course appealing to experimental data in simple, canonical flows. These techniques are now well-accepted and have found application far beyond second-moment closures. [Preview Abstract] |
Tuesday, November 24, 2015 2:21PM - 2:34PM |
R41.00007: My Interactions with John Lumley on the Subject of Passive Scalars Invited Speaker: Zellman Warhaft In the mid nineteen seventies, John Lumley and others were making rapid progress in the development of second order and other models for the prediction of turbulent flows. It became apparent that experiments on the decay of passive scalars (such as temperature fluctuations) in grid turbulence showed large variations, with important consequences for single scale models. With Lumley, I carried out scalar decay measurements and found dependence of the scalar variance decay rate on the initial scalar length scale. These experiments led to many more on passive scalars, both on their large and small-scale characteristics. Here I describe my interactions with John Lumley during this period, and relate it to the work of other groups. I also show that there are still unresolved problems in this area. [Preview Abstract] |
Tuesday, November 24, 2015 2:34PM - 2:47PM |
R41.00008: On turbulence in a stratified environment Invited Speaker: Sutanu Sarkar John Lumley, motivated by atmospheric observations, made seminal contributions to the statistical theory (Lumley and Panofsky 1964, Lumley 1964) and second-order modeling (Zeman and Lumley 1976) of turbulence in the environment. Turbulent processes in the ocean share many features with the atmosphere, e.g., shear, stratification, rotation and rough topography. Results from direct and large eddy simulations of two model problems will be used to illustrate some of the features of turbulence in a stratified environment. The first problem concerns a shear layer in nonuniform stratification, a situation typical of both the atmosphere and the ocean. The second problem, considered to be responsible for much of the turbulent mixing that occurs in the ocean interior, concerns topographically generated internal gravity waves. Connections will be made to data taken during observational campaigns in the ocean. [Preview Abstract] |
Tuesday, November 24, 2015 2:47PM - 3:00PM |
R41.00009: A Brief History of the Lumley 'Projection' Invited Speaker: William George Few ideas in the history have turbulence have generated more intense feelings and reaction than Lumley's 1966 (1) proposal for replacing a random turbulent velocity field by maximizing a deterministic projection upon it. Nor have few ideas been less understood, both by those hostile to it and more recently by some of its advocates. This talk will review what was truly great about Lumley's idea -- the projection itself. And explore briefly some of the sources of the misunderstanding and emotions surrounding it. It will be argued that the original idea still holds the key to moving forward toward a deeper understanding of turbulence. Reference: 1. J. L. Lumley (1967) "The structure of inhomogeneous turbulent flows" in Atmospheric Turbulence and Radio Wave Propagation (A. M. Yaglom and V. I. Tatarsky eds.), Nauka, Moscow, USSR, 166--176. [Preview Abstract] |
Tuesday, November 24, 2015 3:00PM - 3:13PM |
R41.00010: Seismic sounding of convection in the Sun Invited Speaker: Katepalli R. Sreenivasan Thermal convection is the dominant mechanism of energy transport in the outer envelope of the Sun (one-third by radius). It drives global fluid circulations and magnetic fields observed on the solar surface. Convection excites a broadband spectrum of acoustic waves that propagate within the interior and set up modal resonances. These acoustic waves, also called seismic waves, are observed at the surface of the Sun by space- and ground-based telescopes. Seismic sounding, the study of these seismic waves to infer the internal properties of the Sun, constitutes helioseismology. Here we review our knowledge of solar convection, especially that obtained through seismic inference. Several characteristics of solar convection, such as differential rotation, anisotropic Reynolds stresses, the influence of rotation on convection and supergranulation, are considered. On larger scales, several inferences suggest that convective velocities are substantially smaller than those predicted by theory and simulations. This discrepancy challenges the models of internal differential rotation that rely on convective stresses as a driving mechanism and provide an important benchmark for numerical simulations.\\[4pt] In collaboration with Shravan Hanasoge, Tata Institute of Fundamental Research, Mumbai and Laurent Gizon, Max-Planck-Institut fuer Sonnensystemforschung, Goettingen. [Preview Abstract] |
Tuesday, November 24, 2015 3:13PM - 3:26PM |
R41.00011: Decay and Spatial Diffusion of Turbulent Kinetic Energy In The Presence of a Linear Kinetic Energy Gradient Invited Speaker: Charles Meneveau A topic that elicited the interest of John Lumley is pressure transport in turbulence. In 1978 (JL, in Advances in Applied Mechanics, pages 123-176) he showed that pressure transport likely acts in the opposite direction to the spatial flux of kinetic energy due to triple velocity correlations. Here we examine a flow in which the interplay of turbulent decay and spatial transport is particularly relevant. Specifically, using a specially designed active grid and screens placed in the Corrsin wind tunnel, such a flow is realized. Data are acquired using X-wire thermal anemometry at different spanwise and downstream locations. In order to resolve the dissipation rate accurately, measurements are also acquired using the NSTAP probe developed and manufactured by Princeton researchers and kindly provided to us (M. Hultmark, Y. Fan, L. Smits). The results show power-law decay with downstream distance, with a decay exponent that becomes larger in the high kinetic energy side of the flow. Measurements of the dissipation enable us to obtain the spanwise gradient of the spatial flux. One possible explanation for the observations is upgrading transport of kinetic energy due to pressure-velocity correlations, although its magnitude required to close the budget appears very large. Absence of simultaneous pressure velocity measurement preclude us to fully elucidate the observed trends. \\[4pt] In collaboration with Adrien Thormann, Johns Hopkins University. [Preview Abstract] |
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