Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session A12: Turbulence Simulation I |
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Chair: Rayhaneh Akhavan, University of Michigan Room: 315 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A12.00001: Alternative Forcing for Homogeneous Isotropic Turbulence in Real Space G. Mallouppas, B.G.M. van Wachem, W.K. George An alternative to the linear forcing of Lundgren [1] is suggested for sustaining homogeneous and isotropic turbulence. The method depends on a random pseudo-velocity field produced initially from an arbitrary spectrum. Energy can be fed into a variety of different range of wavenumbers so that the resulting total turbulent kinetic energy remains constant. This talk will first introduce the methodology used to obtain 1D spectra and correlation functions which will then be used to validate the homogeneity and isotropy of the sustained turbulence. The effects of window functions on 1D spectra and correlations will be also addressed. Finally, the effect of initial conditions (i.e. triggering at different wavenumbers) on the statistics, especially spectra and correlation functions will be investigated, with a particular view toward understanding the variety of spectra generated by experiments, e.g., [2,3].\\[4pt] [1] Lundgren, T. S. \ (2003) \ Ann. Res. Briefs, CTR, Stanford\\[0pt] [2] Comte-Bellot, G.\ and Corrsin, S.\ (1971) JFM, 48, 273-337.\\[0pt] [3] Seoud, R.\ and Vassilicos, J.\ C.\ (2007) Phys Flds. 19. [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A12.00002: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A12.00003: Methods and issues for highly-scalable simulation of isotropic homogeneous turbulence Orlando Ayala, Charles Andersen, Hossein Parishani, Lian-Ping Wang Direct numerical simulations (DNS) of homogeneous isotropic turbulence have served as a reliable quantitative research tool for studying the physics and dynamics of small-scale turbulence. It is desirable to extend the range of scales or equivalently the flow Reynolds number so a more complete understanding of related physical processes can be obtained. While the pseudo-spectral method is known to be the most accurate DNS approach, it has the challenge of performing global data communication (i.e., Fast Fourier Transform) which may not scale well on the state-of-the-art PetaScale computers with O(100,000) processors. Alternative approaches, such as high-order finite difference, finite-volume, and lattice Boltzmann equation, have been proposed to replace the pseudo-spectral method. The question we wish to address in this talk is: how do different approaches compare in terms of accuracy and parallel efficiency? Complexity analyses of several approaches will be discussed and be used to understand scalability data obtained from several parallel computers. The simulated flows will also be compared to examine the resolution requirements for various approaches to achieve a comparable accuracy. Detailed implementation issues related to multi-dimensional domain decompositions and large-scale forcing scheme will be discussed. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A12.00004: A comparison between eddy-viscosity models and direct numerical simulation: the response of turbulent flow to a volume force Paolo Luchini, Serena Russo Inspired by P. Luchini \& F. Charru's\footnote{Luchini, P., Charru, F., The phase lead of shear stress in shallow-water flow over a perturbed bottom, \textit{J. Fluid Mech.} \textbf{665}, 516-539 (2010)} analysis of the phase lead of the wall-shear stress at a channel's perturbed bottom, we identified a benchmark problem simple enough that it can be solved both by an eddy-viscosity model, similar to those typically used in shallow-water flow calculations, and by direct numerical simulation. This is the linear response of a turbulent flow's mean-velocity profile to an external volume force. Such a force, of unspecified origin in the present context, was found in\footnote{Ibid.} to be representative of the perturbation induced by bottom topography, and its consequences were analysed by means of an eddy-viscosity model. On the other hand, a modification of Luchini, Quadrio \& Zuccher's\footnote{Luchini, P., Quadrio, M., Zuccher, S., The phase-locked mean impulse response of a turbulent channel flow, \textit{Phys. Fluids} \textbf{18}, 121702 (2006).} method to compute the linear impulse response of a wall-bounded turbulent flow allows the response to a volume force to be computed directly. The comparison exhibits significant differences and suggests that there might be fundamental obstacles to designing an eddy-viscosity model that provides the correct result. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A12.00005: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A12.00006: DNS of very strong adverse pressure gradient flows with eventual separation Guillermo Araya, Luciano Castillo Direct Numerical Simulations (DNS) of spatially-evolving turbulent boundary layers with prescribed very strong adverse pressure gradients with eventual separation are performed. The driven force behind this investigation is to analyze the interaction between the inner and outer layers in separated flows. Also, the outer peaks in velocity fluctuations are analized by means of the energy budget of the turbulent kinetic energy and shear Reynolds stresses. A method for prescribing realistic turbulent velocity inflow boundary conditions is employed and based on the rescaling-recycling method proposed by Lund et al. (1998). The standard rescaling process requires prior knowledge about how the appropriate velocity and length scales are related between the inlet and recycle stations (e.g. classic scaling laws). Here a dynamic approach is proposed in which such information is deduced dynamically by involving an additional plane, the so called ``test plane'' located between the inlet and recycle stations. The approach also distinguishes between the inner and outer regions of the boundary layer and enables the use of multiple velocity scales, Araya et al. (2009, 2011). This flexibility allows applications to boundary layer flows with arbitrary pressure gradients. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A12.00007: Slow Growth Formulation for DNS of Temporally Evolving Boundary Layers Victor Topalian, Onkar Sahni, Todd Oliver, Robert Moser A formulation for DNS of temporally evolving boundary layers is developed and demonstrated. The formulation relies on a multiscale approach to account separately for the slow time evolution of statistical averages, and the fast time evolution of turbulent fluctuations. The source terms that arise from the multiscale analysis are modeled assuming a self-similar evolution of the averages. The performance of the formulation is evaluated using DNS of spatially evolving compressible boundary layers. This formulation was developed to provide data for the calibration of turbulence model parameters and enable the quantification of uncertainty due to the models. The extension of this formulation to homogenize spatially evolving boundary layers will also be discussed. This work is supported by the Department of Energy [National Nuclear Security Administration] under Award Number [DE-FC52-08NA28615]. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A12.00008: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A12.00009: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A12.00010: Dynamics of large-scale coherent structures in developing and fully developed channel flow over a rough wall Kyoungsik Chang, George Constantinescu LES of fully developed and developing channel flow are conducted to study the formation and structure of the streaks for the case when the rough bed consists of an array of identical sinusoidal waves with an amplitude of 0.1$\lambda $, where $\lambda $ is the wave wavelength. The channel depth is $\lambda $, its width is 10$\lambda $ and the channel Reynolds number is 6,700. Consistent with experimental investigations, the average spanwise spacing of the streaks predicted by LES is close to 1.5$\lambda $ in the case of a fully developed flow. A developing channel flow simulation with steady inflow conditions reveals the streaks form as a result of the break up of the quasi two-dimensional spanwise-oriented eddies forming in the shear layers past the crests of the first waves into arrays of pronounced hairpin vortices. These hairpins scale with the size of the waves which is of the order of the channel depth. Streaks are observed starting in the region where the flow transitions to turbulent. In average, the streaks become larger as one moves downstream until fully developed conditions are reached. [Preview Abstract] |
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