Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H34: Turbulence: LES Models and Methods |
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Chair: Mahdi Abkar, Stanford University Room: Oregon Ballroom 203 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H34.00001: Modeling and large-eddy simulation (LES) of a turbulent boundary layer over linearly-varying surface roughness A. Sridhar, D. I. Pullin, W. Cheng An empirical model is presented, after Rotta (1962), that describes the development of a fully-developed turbulent boundary layer in the presence of surface roughness with nominal roughness length-scale $k_s$ that varies with stream-wise distance $x$. For $Re_x = U_e(x)\,x/\nu$ large, use is made of the log-wake model of the local turbulent mean-velocity profile that contains the Hama roughness correction $\Delta U^+(k_s^+)$ for the asymptotic, fully rough regime. It is shown that the skin friction coefficient $C_f$ is constant in $x$ only for $k_s = \alpha x$, where $\alpha$ is a dimensionless number. For $U_e(x)=A\,x^m$, this then gives a two-parameter $(\alpha,m)$ family of solutions for boundary-layer flows that are self similar in the variable $z/(\alpha\,x)$ where $z$ is the wall-normal co-ordinate. Trends observed in this model are supported by wall-modeled LES of the zero-pressure-gradient turbulent boundary layer ($m=0$) at very large $Re_x$. It is argued that the present results suggest that, in the sense that $C_f$ is spatially constant and independent of $Re_x$, this class of flows can be interpreted as providing the asymptotically-rough equivalent of Moody-like diagrams for boundary layers in the presence of small-scale roughness. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H34.00002: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 11:06AM - 11:19AM |
H34.00003: Subgrid-scale models for large-eddy simulation of rotating turbulent flows Maurits Silvis, Xavier Trias, Mahdi Abkar, Hyunji Jane Bae, Adrian Lozano-Duran, Roel Verstappen This paper discusses subgrid models for large-eddy simulation of anisotropic flows using anisotropic grids. In particular, we are looking into ways to model not only the subgrid dissipation, but also transport processes, since these are expected to play an important role in rotating turbulent flows. We therefore consider subgrid-scale models of the form $ \tau = -2\nu_t S + \mu_t (S \Omega-\Omega S) $, where the eddy-viscosity $\nu_t$ is given by the minimum-dissipation model, $\mu_t$ represents a transport coefficient; $S$ is the symmetric part of the velocity gradient and $\Omega$ the skew-symmetric part. To incorporate the effect of mesh anisotropy the filter length is taken in such a way that it minimizes the difference between the turbulent stress in physical and computational space, where the physical space is covered by an anisotropic mesh and the computational space is isotropic. The resulting model is successfully tested for rotating homogeneous isotropic turbulence and rotating plane-channel flows. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H34.00004: Large-eddy simulations of viscoelastic isotropic turbulence with the FENE-P fluid Fernando T. Pinho, Pedro O. Ferreira, Carlos B. da Silva A new subgrid-scale (SGS) model developed for large-eddy simulations (LES) of dilute polymer solutions described by the Finitely Extensible Nonlinear Elastic constitutive equation closed with the Peterlin approximation (FENE-P), is presented. The filtered conformation tensor evolution equation uses the {\it self-similarity} of the polymer stretching terms, and the {\it global equilibrium} of the trace of the conformation tensor, while the SGS stresses are modelled with the classical Smagorinsky model. The new closure is assessed in direct numerical simulations (DNS) of forced isotropic turbulence using classical {\it a-priori} tests, and in {\it a-posteriori} (LES) showing excellent agreement with all the exact (filtered DNS) results. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H34.00005: A minimum dissipation scalar transport model for large-eddy simulation of turbulent flows Mahdi Abkar, Hyun J. Bae, Parviz Moin Minimum-dissipation models are a simple alternative to the Smagorinsky-type approaches to parameterize the sub-filter scale turbulent fluxes in large-eddy simulation. A recently derived minimum-dissipation model for sub-filter stress tensor is the AMD model (Rozema et al., Phys. Fluids, 2015) and has many desirable properties. It is more cost effective than the dynamic Smagorinsky model, it appropriately switches off in laminar and transitional flows, and it is consistent with the theoretic sub-filter stress tensor on both isotropic and anisotropic grids. In this study, an extension of this approach to modeling the sub-filter scalar flux is proposed. The performance of the AMD model is tested in the simulation of a high Reynolds number, rough wall, boundary layer flow with a constant and uniform surface scalar flux. The simulation results obtained from the AMD model show good agreement with well-established empirical correlations and theoretical predictions of the resolved flow statistics. In particular, the AMD model is capable to accurately predict the expected surface-layer similarity profiles and power spectra for both velocity and scalar concentration. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H34.00006: Towards a transport model for epistemic UQ in RANS closures Wouter Edeling, Gianluca Iaccarino Due to their computational efficiency, Reynold-Averaged Navier-Stokes (RANS) turbulence models remain a vital tool for modeling turbulent flows. However, it is well known that RANS predictions are locally corrupted by epistemic model-form uncertainty. Whereas some Uncertainty Quantification (UQ) approaches attempt to quantify this uncertainty by considering the model coefficients as random variables, we directly perturb the Reynold-stress tensor at locations in the flow domain where the modeling assumptions are likely to be invalid. Inferring the perturbations on a point-by-point basis would lead to a high-dimensional problem. To reduce the dimensionality, we propose separate model equations based on the transport of linear invariants of the anisotropy tensor. This provides us with a low-dimensional UQ framework where the invariant transport model decides on the magnitude and direction of the perturbations. Where the perturbations are small, the RANS result is recovered. Using traditional turbulence modeling practices we derive weak realizability constraints, and we will rely on Bayesian inference to calibrate the model on high-fidelity data. We will demonstrate our framework on a number of canonical flow problems where RANS models are prone to failure. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H34.00007: Three-dimensional Diffusive Strip Method. Daniel Martinez-Ruiz, Patrice Meunier, Laurent Duchemin, Emmanuel Villermaux The Diffusive Strip Method (DSM) is a near-exact numerical method developed for mixing computations at large Péclet number in two-dimensions ({\it J. Fluid Mech. \bf 662}, (2010)). The method consists in following stretched material lines to compute a-posteriori the resulting scalar field is extended here to three-dimensional flows, following surfaces. We describe its 3D peculiarities, and show how it applies to a simple Taylor-Couette configuration with non-rotating boundary conditions at the top end, bottom and outer cylinder. This flow produces an elaborate, although controlled, steady 3D flow which relies on the Ekman pumping arising from the rotation of the inner cylinder is both studied experimentally, and numerically modeled. A recurrent two-cells structure appears formed by stream tubes shaped as nested tori. A scalar blob in the flow experiences a Lagrangian oscillating dynamics with stretchings and compressions, driving the mixing process, and yielding both rapidly-mixed and nearly pure-diffusive regions. A triangulated-surface method is developed to calculate the blob elongation and scalar concentration PDFs through a single variable computation along the advected blob surface, capturing the rich evolution observed in the experiments. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H34.00008: A Fractional PDE Approach to Turbulent Mixing; Part I: an Anomalous Transport Theory Mohsen Zayernouri, Mehdi Samiee It has been experimentally and theoretically shown that even in the most ideal cases of homogeneous and isotropic turbulence, the statistical distributions are asymmetric and heavy-tailed. Similar observations, in addition to high peaks, have been made in grid turbulence and atmospheric boundary layer. In the aforementioned problems, the skewness, as a measure of asymmetry, is non-zero and negative, also the flatness (kurtosis), as a notion of the tail heaviness in the distribution, significantly exceeds the Gaussian value 3, reflecting a strong non-Gaussianity. In this talk, we demonstrate that the existence of such \textit{anomalous characteristics} e.g., heavy tails, asymmetric distributions, and high peaks can naturally put the phenomenology of Taylor, Richardson, and Kolmogorov in broader framework, where the generalizing fractional Brownian motions and stochastic L\'evy jump processes (or L\'evy flights), investigated in the context of fractional PDEs in the fluid limit, can physically and mathematically explain, hence, predict the notion of anomalously enhanced (sub-to-super) diffusion and self-similar features in passive scalar turbulence. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H34.00009: A Fractional PDE Approach to Turbulent Mixing; Part II: Numerical Simulation Mehdi Samiee, Mohsen Zayernouri We propose a generalizing fractional order transport model of advection-diffusion kind with fractional time- and space-derivatives, governing the evolution of passive scalar turbulence. This approach allows one to incorporate the nonlocal and memory effects in the underlying anomalous diffusion i.e., \textit{sub-to-standard} diffusion to model the trapping of particles inside the eddied, and \textit{super-diffusion} associated with the sudden jumps of particles from one coherent region to another. For this nonlocal model, we develop a high order numerical (spectral) method in addition to a fast solver, examined in the context of some canonical problems. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H34.00010: Quantum speed-up for turbulent mixing simulation Guanglei Xu, Andrew Daley, Peyman Givi, Rolando Somma Quantum computing techniques have the potential in the future to generate revolutionary advances in many types of computation. The necessary hardware is under rapid development, making it an opportune time to identify possible specific applications across a range of fields, and properly identify the potential of this new paradigm of computing. Turbulent mixing simulation is important in a variety of fields, and is typically accomplished by Monte Carlo methods. To reach high precision in estimating parameters often requires vast computational resources. We have developed a quantum algorithm for turbulent mixing simulation that provides a quadratic speed-up over Monte Carlo methods in terms of number of repetitions needed to achieve designated accuracy. Taking the example of binary scalar mixing process described by a coaslescence/dispersion model, we demonstrate the advantages of our quantum algorithm by illustrating comparisons of statistical error scaling to repetition number between Monte Carlo method and quantum algorithm. This is an important starting point to further understand how quantum algorithms can be directly applied in fluid dynamics, and to estimate the timescales on which quantum hardware will have useful applications in this area of science. [Preview Abstract] |
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