Download or read book Subgrid scale Modeling and Wavelet Analysis for Preferential Concentration of Inertial Point Particles in Turbulent Flows written by Maxime Bassenne and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A striking feature of particle-laden turbulent flows is the presence of particle clouds that result from the tendency of inertial particles to preferentially sample specific regions of the flow field. This phenomenon is central to a number of important physical processes. However, computational predictions of preferential concentration at high Reynolds numbers are challenging, since the numerical resolution of the participating scales is typically unaffordable. This dissertation contributes both to the analysis of the preferential concentration phenomenon and the development of subgrid-scale models for the prediction of preferential concentration in large-eddy simulations of particle-laden turbulence. First, direct numerical simulations of incompressible homogeneous-isotropic turbulence laden with a dilute suspension of inertial point particles are performed in conjunction with a wavelet multi-resolution analysis of the results. The use of spatially localized wavelet basis functions enables the simultaneous consideration of physical and scale spaces in the spectral characterization of the flow field of the carrier phase and the concentration field of the disperse phase. The multi-resolution analysis of the disperse phase provides statistical information about the spatial variability of a scale-dependent coarse-grained number density field and the local energy spectra of its fluctuations, characterizing the sensitivities of those quantities to variations in scale and Stokes number. In particular, the spatial variabilities of the wavelet energy spectrum of the particle concentration fluctuations are observed to be maximum in regimes where the particles preferentially concentrate. The results highlight the scale-dependent inhomogeneities of the structures in the concentration field generated by preferential concentration, and the existence of characteristic scales of interaction between the disperse and carrier phases. Additionally, an inter-phase multi-resolution analysis is performed that indicates the occurrence of a spatial anti-correlation between the enstrophy and kinetic-energy spectra of the carrier phase and the particle concentration at small scales in regimes where preferential concentration is important. This anti-correlation vanishes as the scale is increased, and is largely suppressed when the preferential-concentration effect is negligible. Secondly, a wavelet-based method for extraction of clusters of inertial particles in turbulent flows is presented that is based on decomposing Eulerian particle number-density fields into the sum of a coherent (organized) and an incoherent (disorganized) components. The coherent component is associated with the clusters and is extracted by filtering the wavelet-transformed particle number-density field based on an energy threshold. The analysis shows that in regimes where the preferential concentration is important, the coherent component representing the clusters can be described by just 1.6% of the total number of wavelet coefficients, thereby illustrating the sparsity of the particle number-density field. On the other hand, the incoherent portion is visually structureless and much less correlated that the coherent one. An application of the method is illustrated in the form of a grid-adaptation algorithm that results in non-uniform meshes with fine and coarse elements near and away from particle clusters, respectively. In regimes where preferential concentration in clusters is important, the grid adaptation leads to a reduction of the number of control volumes by one to two orders of magnitude. Thirdly, two dynamic models for turbulent velocity fluctuations are proposed for large-eddy simulations of dispersed multiphase flows. The first model is simple, involves no significant computational overhead, contains no adjustable parameters, and is flexible enough to be deployed in any type of flow solvers and grids, including unstructured setups. The approach is based on the use of elliptic differential filters to model the subgrid-scale velocity. The only model parameter, which is related to the nominal filter width, is determined dynamically by imposing consistency constraints on the estimated subgrid energetics. The second model constructs a velocity that contains scales smaller than the coarse-grid resolution, thereby enabling the prediction of small-scale phenomena such as the preferential concentration of particles in high-strain regions. The construction of the spectrally enriched velocity field in physical space is made dynamically, and is based on 1) modeling the smallest resolved eddies of sizes comparable to the grid size via approximate deconvolution, and 2) reconstructing the subgrid-scale fluctuations via non-linear generation of small-scale turbulence. The model does not contain tunable parameters, can be deployed in non-uniform grids, and is applicable to inhomogeneous flows subject to arbitrary boundary conditions. The performance of both models is tested in large-eddy simulations of homogeneous-isotropic turbulence laden with particles, where improved agreement with direct numerical simulation results is obtained for the statistics of preferential concentration. Lastly, application to wall-modeled large-eddy simulations of particle-laden channel flow is presented. Results of the application of existing wall models to particle-laden turbulent channel flows are described, and prospective pathways for improving their performance are suggested. The focus is on the prediction of the spatial distribution statistics of the disperse phase. It is observed that wall-modeled large-eddy simulations without particular treatment for the particles in the wall-adjacent cells overpredict the near-wall accumulation of particles. The choice of the continuous representation of the velocity field between the first grid point and the wall is shown to be of primary importance. A wall-modeling strategy is explored that performs well at large Stokes numbers. It relies on using interpolation kernels near the wall that mimic the law of the wall for the wall-parallel velocity, and direct numerical simulation profiles of the fluctuations for the wall-perpendicular velocity. Applications of the two developed subgrid-scale models are shown to improve the prediction of preferential concentration, but have no effect on the mean concentration profile.

Download or read book New Subgrid Models for Inertial Particles in Large eddy Simulations of Turbulent Flows written by Baidurja Ray and published by . This book was released on 2013 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: An initially uniform distribution of inertial particles will spontaneously organize themselves into clusters in a turbulent flow, driven primarily by the small-scale turbulent fluctuations. Accurate prediction of such clustering of inertial particles, along with their relative velocity statistics, is essential for computing their binary collision rates, an important quantity that determines the evolution of the size distribution of these particles, under conditions when collisions lead to agglomeration or coalescence. In large-eddy simulations (LES) of turbulent flows, only the largescale turbulent fluctuations are represented on the grid whereas the small-scales (or subgrid scales) need to be modeled. None of the existing LES subgrid models are able to accurately predict the particle collision rates across the entire range of particle inertia, where inertia is parameterized by the Stokes number (St) defined as the ratio of the particle response time to the Kolmogorov time-scale ([tau][eta]). In this work, we present new subgrid models designed to recover the clustering and relative velocity statistics of inertial particles. We begin by considering the effect of the subgrid scales on our statistics of interest. We do this by analyzing the exact distribution of particles obtained from direct numerical simulations (DNS) and comparing them with the ones obtained from a filtered DNS (FDNS). FDNS is obtained by filtering out the 'subgrid' scales and represents a 'perfect' LES with an exact representation of the large-scales (free of any subgrid modeling error). This provides a benchmark study and points to the need of incorporating the mech-anism by which the small-scales affect particle statistics, into the LES subgrid models designed to recover clustering and relative velocities of inertial particles. We then consider a subgrid model based on kinematic simulations of turbulence (so-called KSSGM), and show that it can accurately predict the relative velocity statistics for all St, but can capture clustering only for St>= 2.0. We investigate the reasons for its failure to predict clustering at St

Download or read book A Multifractal Subgrid scale Model for Large eddy Simulation of Turbulent Flows written by Gregory Charles Burton and published by . This book was released on 2003 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book 3D Vector Wavelet Based Subgrid Scale Model for LES of Nonequilibrium Turbulence written by and published by . This book was released on 1995 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have laid the foundation to develop and validate LES using wavelets as a functional basis and based on subgrid scale (SGS) modeling using vector wavelets. Wavelet LES (WLES) consists of subgridscale model equations (SSM) and space-resolved model (SRM) equations. Using a vector wavelet decomposition of the velocity field a simple model for locally isotropic turbulence has been derived from the Navier-Stokes equation. This model, which involves no empirical or adhoc parameter Incorporates nonlocal inter-scale interactions, reveals backscatter and can be applied to represent small-scale turbulence in LES schemes. Stationary solutions of the model equation & produce the Kolmogorov k(5/3) inertial spectrum and the k(4) infra-red spectrum. We have completed derivation of the SRM equations based on the helical wave decomposition. We will test the SRM equations using the computational resources in this NAS operational year. A wavelet-based subgrid-scale model (WSSM) will be generalized to account for anisotropic and inhomogeneous turbulence in wall-bounded flows and will employ a nonuniform grid to resolve the near-wall structures. (AN).

Download or read book On the Subgrid scale Modeling of Compressible Turbulence written by C. G. Speziale and published by . This book was released on 1987 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation of Subgrid scale Turbulence Models Using a Fully Simulated Turbulent Flow written by Robert Arthur Clark and published by . This book was released on 1977 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book New Approaches in Modeling Multiphase Flows and Dispersion in Turbulence Fractal Methods and Synthetic Turbulence written by F.C.G.A. Nicolleau and published by Springer Science & Business Media. This book was released on 2011-10-29 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains a collection of the main contributions from the first five workshops held by Ercoftac Special Interest Group on Synthetic Turbulence Models (SIG42. It is intended as an illustration of the sig’s activities and of the latest developments in the field. This volume investigates the use of Kinematic Simulation (KS) and other synthetic turbulence models for the particular application to environmental flows. This volume offers the best syntheses on the research status in KS, which is widely used in various domains, including Lagrangian aspects in turbulence mixing/stirring, particle dispersion/clustering, and last but not least, aeroacoustics. Flow realizations with complete spatial, and sometime spatio-temporal, dependency, are generated via superposition of random modes (mostly spatial, and sometime spatial and temporal, Fourier modes), with prescribed constraints such as: strict incompressibility (divergence-free velocity field at each point), high Reynolds energy spectrum. Recent improvements consisted in incorporating linear dynamics, for instance in rotating and/or stably-stratified flows, with possible easy generalization to MHD flows, and perhaps to plasmas. KS for channel flows have also been validated. However, the absence of "sweeping effects" in present conventional KS versions is identified as a major drawback in very different applications: inertial particle clustering as well as in aeroacoustics. Nevertheless, this issue was addressed in some reference papers, and merits to be revisited in the light of new studies in progress.

Download or read book Modeling of Subgrid scale Effects on Particles in Large eddy Simulation of Turbulent Two phase Flows written by Babak Bahram Shotorban and published by . This book was released on 2005 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structure of Turbulence and Subgrid Scale Modeling written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Transformation from homogeneous to nonhomogeneous turbulent flows is developed, based on some properties of the Navier-Stokes equations. This transformation is successfully applied to the turbulent wake, produced by a model-scale frigate. Some new schemes for the large-eddy simulations of turbulent flows are developed, tested by direct numerical simulations and compared with experiments.

Download or read book Evaluation of Subgrid scale Turbulence Models Using a Fully Siimulated Turbulent Flow written by R. A. Clark and published by . This book was released on 1977 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper begins with a brief discussion of the general approach to the numerical simulation of turbulent flows. The traditional approaches have been based on Reynolds' original idea of averaging the Navier-Stokes equations over.

Download or read book Divergence free Wavelets for the Analysis and Simulation of Turbulent Flows written by Cem Musa Albukrek and published by . This book was released on 2002 with total page 344 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Dynamic Subgrid scale and Wall Models for Turbulent Boundary Layers written by Hyun Ji Bae and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Most turbulent flows cannot be calculated by direct numerical simulation (DNS) of the Navier-Stokes equations because the range of scales of motions is so large that the computational cost becomes prohibitive. In large-eddy simulation (LES), only the large eddies are resolved and the effect of the small scales on the larger ones is modeled through a subgrid-scale (SGS) model. Given that accurate representation and prediction of turbulence is needed in many engineering and scientific applications, development of accurate yet computationally efficient SGS models is an important task. Additionally, wall models are necessary to overcome the prohibitive near-wall resolution requirements for the large scales in high-Reynolds-number turbulent flows. This study investigates a new SGS model, the anisotropic minimum-dissipation (AMD) model, which is constructed to provide the minimum eddy viscosity required to avoid energy pile-up in the smallest resolved scales. The AMD model is successfully applied in simulations of decaying grid turbulence for isotropic grids, and temporal mixing layer and turbulent channel flow for anisotropic grids. This model is more cost-effective than the dynamic Smagorinsky model (DSM) and appropriately switches off in laminar and transitional flows. The formulation of the AMD model is extended to the transport equation for scalar concentration to model the subfilter scalar flux. The performance of the model is tested in the simulation of high-Reynolds-number rough-wall boundary-layer flow with a constant and uniform surface scalar flux. The simulation results obtained from the scalar model show good agreement with well-established empirical correlations and theoretical predictions of the resolved flow statistics. The accuracy of the SGS models is tested by studying the convergence properties in the outer region of a channel flow at moderate to high Reynolds numbers. As LES requires scale separation of the resolved and subgrid scales, the convergence study must be conducted in high-Reynolds-number flows. However, the analysis shows that the errors from the near-wall region are dominant for SGS models in usual LES grid resolutions, where the grid is not refined in the wall-parallel directions. For evaluation of SGS models, in order to overcome the grid requirements imposed by the near-wall turbulent eddies as well as the errors accumulated near the wall, a possible solution is to isolate the outer region of wall-bounded flows. This is made possible by one of two ways: suppressing the near-wall dynamics through a modified wall, or supplying the correct mean stress at the wall with a wall model. Theoretical analysis of the error scaling of SGS models for the mean velocity profile, turbulence intensities, and energy spectra is performed. The numerical convergence studies of the DSM and AMD models show that both models are first-order accurate in terms of the mean velocity profile, which is consistent with the theoretical assessments. Lastly, a new dynamic wall model based on the slip boundary condition is proposed. The use of the slip boundary condition for wall-modeled LES is motivated through theoretical analysis and a priori study of DNS data. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel and flat-plate turbulent boundary layer. The slip boundary condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. The requirements for the slip lengths to be used in conjunction with wall models are discussed, and the equation that connects the slip boundary condition with the stress at the wall is derived. A dynamic procedure based on the invariance of wall stress under test filtering is formulated for the slip condition, providing a dynamic slip wall model free of any a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow, and zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict mean and turbulence intensities for various flow configurations, Reynolds numbers, and grid resolutions.

Download or read book Dynamic Subgrid scale Modeling for Large eddy Simulation of Turbulent Flows with a Stabilized Finite Element Method written by Andres E. Tejada-Martinez and published by . This book was released on 2002 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dynamic Subgrid scale Modeling for Finite Element Based Simulation of Complex Turbulent Flows written by Steven Tran and published by . This book was released on 2016 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Point Particle Model for Disperse Turbulent Flows written by and published by . This book was released on 2009 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Toward the Large Eddy Simulation of Compressible Turbulent Flows written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-10-24 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: New subgrid-scale models for the large-eddy simulation of compressible turbulent flows are developed and tested based on the Favre-filtered equations of motion for an ideal gas. A compressible generalization of the linear combination of the Smagorinsky model and scale-similarity model, in terms of Favre-filtered fields, is obtained for the subgrid-scale stress tensor. An analogous thermal linear combination model is also developed for the subgrid-scale heat flux vector. The two dimensionless constants associated with these subgrid-scale models are obtained by correlating with the results of direct numerical simulations of compressible isotropic turbulence performed on a 96(exp 3) grid using Fourier collocation methods. Extensive comparisons between the direct and modeled subgrid-scale fields are provided in order to validate the models. A large-eddy simulation of the decay of compressible isotropic turbulence (conducted on a coarse 32(exp 3) grid) is shown to yield results that are in excellent agreement with the fine grid direct simulation. Future applications of these compressible subgrid-scale models to the large-eddy simulation of more complex supersonic flows are discussed briefly. Erlebacher, G. and Hussaini, M. Y. and Speziale, C. G. and Zang, T. A. Langley Research Center NAS1-18605

Download or read book Tests of Subgrid Scale Models in Strained Turbulence Studies of the Structure of Homogeneous Shear Flows Developing a Model of Turbulence Near a Wall from Solutions of the Navier Stokes Equations written by J. H. Ferziger and published by . This book was released on 1982 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three studies are described, each of which makes use of turbulent flow fields calculated using the Navier-Stokes equations. In the first study, exact numerical solutions of the full Navier-Stokes equations are used to evaluate subgrid-scale models used in large-eddy simulations. The flows investigated are homogeneous and incompressible with strong imposed mean strain or shear. Models evaluated include the conventional Smagorinsky model as well as a recently introduced formulation based on the notion of scale similarity. In the second study, exact numberical simulations of homogeneous shear flows are examined using various computer-graphic tools, the aim being to attempt to understand the mechanisms underlying the production of turbulence energy and growth of length scales in such flows. The subject of the third study is the development of a computational model of the viscous sublayer of wall-bounded incompressible turbulent flow. In this work, the time-dependent Navier-Stokes equations, suitably simplified, are solved subject to boundary conditions imposed at the outer edge of the viscous sublayer. The formulation of these edge conditions so that computed average distributions of turbulence quantities agree with experimental data through the sublayer is the essence of work.