Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A16: Advances in LES Modeling I |
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Chair: Sanjeeb Bose, Stanford Room: 4c3 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A16.00001: Towards large-eddy simulation of maneuvering vehicles using an unstructured overset grid method Nick Morse, Wyatt Horne, Krishnan Mahesh We discuss the development of large-eddy simulation (LES) capability towards the simulation of maneuvering vehicles using the novel unstructured overset numerical algorithm developed by Horne and Mahesh [J. Comput. Phys (2019) 376:585-596]. This method addresses the discrete conservation and scaling challenges of overset methodologies and allows for simulation of flows around complex moving bodies undergoing six degree-of-freedom (6 DOF) motion. We discuss the application of this method to two problems of interest. First, simulations are performed of flow over an axisymmetric body of revolution with comparison to experimental data and previous LES studies. Second, a controller is integrated with the overset method’s 6 DOF solver to control of the motion of the body in external fluid flow. Validation examples and applications are discussed. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A16.00002: Wall-modeled LES of rough-wall flows using the amplitude modulation framework Sicong Wu, Kenneth Christensen, Paul Fischer, Carlos Pantano The framework of amplitude modulation (AM) is ideally suited for the wall-modeled LES of turbulent boundary layer flows since the only model input is the large-scale flow information in the outer resolved region by LES. Adapted from the predictive models pioneered by Mathis et al. (2011) and Mathis et al. (2013), wall-boundary conditions (velocities and wall shear stresses) at the first wall-normal grid point maintained in the log region are proposed for turbulent flow over rough walls, where the model coefficients are calibrated from available DNS and experiments and the universal signals are generated using synthetic turbulence of specified energy spectrum and Reynolds stresses. Statistics including the mean velocity, turbulent stresses and dissipation will be collected and compared to the reference data. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A16.00003: Dynamic slip wall model for compressible turbulent flows Kevin Griffin, Sanjeeb Bose, Parviz Moin The dynamic slip wall model (Bose and Park, ARFM, 2018) for LES is extended to compressible flows. Slip boundary conditions are used for velocity and temperature, and the slip lengths are computed dynamically. The slip wall boundary condition is a new paradigm for wall modeled LES that does not rely on RANS modeling used in traditional wall modeled LES. In this presentation, the slip wall model is applied to a transonic, transitional turbine inlet guide vane (Arts and de Rouvroit, ASME J. Turbomachinery, 1992), using unstructured CharLES code. The slip wall model is applied uniformly to the laminar, transitional, and turbulent sections of the flow. No a priori knowledge of the transition location is needed. The heat transfer on the blade is well predicted using the slip wall model. The use of a slip wall model in the under-resolved laminar section is motivated with an analysis of how slip improves the numerical prediction of the self-similar Falkner-Skan equation with limited resolution. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A16.00004: Numerical Dissipation and Subgrid-scale Modeling for High-order DG Schemes David Flad, Scott Murman Using high-order discontinuous-Galerkin (DG) methods for large-eddy simulation (LES) continues to increase in popularity. The methods are often favored over high-order finite-difference schemes due to their geometrical flexibility, dense numerical operators, and minimal inter-processor communication. Often the methods are used with no explicit LES model added, relying on the inherent dissipation of the method to account for unresolved stresses, i.e. implicit LES. In order to obtain nonlinear stability polynomial de-aliasing (``exact'' numerical quadrature) is frequently applied. In the current work, we analyze the quality of LES for a high-order implicit time discretization and various high-order spatial discretizations, with a focus on the different effects of inherent numerical dissipation of the schemes. Dissipation-free spatial operators are used to separate modeling terms and discretization errors. The suitability and limitation for high Reynolds number turbulent flows is analyzed and compared to results when adding an explicit subgrid-scale model, such as the Smagorinsky model. Results are presented for decaying homogeneous isotropic turbulence and wall-bounded channel flow. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A16.00005: SGS Model Based on Removal of Small-Scale Energy Production through Nonlinear Interactions Julian Domaradzki, Guangrui Sun Nonlinear dispersive SGS models are not sufficiently dissipative in actual LES. In this work a new nonlinear model is proposed to remove the unphysical energy accumulation near the LES cutoff. The model is derived based on the analysis of the nonlinear energy transfer among scales of different size and can be regarded as a direct removal of the energy production in targeted regions. We compare the present model with other nonlinear models and regularization techniques both theoretically and numerically. We show that through the removal of energy production in a targeted region of scales in the vicinity of the LES cutoff the new model is able to provide sufficient SGS dissipation in actual LES. The scale separation is facilitated by a smooth low-pass filter, which becomes increasingly more active for smaller resolved scales. Since the filter already takes grid size into account, the model is found to consistently produce accurate results in a posteriori tests in LES of turbulent channel flow at various grid resolutions and Reynolds numbers. Our results demonstrate that the energy pileup at small resolved scales in insufficiently dissipative LES can be removed by a simple modification of the nonlinear term without a need for extra dissipative terms such as an eddy-viscosity model. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A16.00006: An algebraic non-equilibrium wall-stress model for LES by analytically integrating the TBLE Kazuhiko Suga, Tomoki Sakamoto, Yusuke Kuwata An algebraic non-equilibrium wall-stress model for large eddy simulation is proposed. The ordinary differential equation (ODE) of the thin-layer approximated momentum equation including the temporal, convection, and pressure gradient terms is considered to form the wall-stress model. Applying the ideas of the analytical wall function for Reynolds averaged turbulence models, the profile of the sub-grid-scale eddy viscosity inside the wall adjacent cells is modeled as two-segment piecewise linear variations. This simplification makes it possible to analytically integrate the ODE near the wall to algebraically give the wall shear stress as the wall boundary condition for the momentum equation. By applying such integration to the wall-normal velocity component, the methodology to avoid the log-layer mismatch is also proposed. Coupled with the standard Smagorinsky model, the proposed model shows good performance in turbulent channel flows at $Re_\tau=1000-5000$ irrespective of the grid resolutions. The proposed model is also confirmed to be superior to the traditional equilibrium wall stress model in a turbulent backward-facing step flow. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A16.00007: Fractional gradient based subgrid-scale models of turbulence Patricio Clark Di Leoni, Tamer Zaki, George Karniadakis, Charles Meneveau In large eddy simulations, the effects of the unresolved scales are encapsulated in the turbulence subgrid-scale model. Whether the model can reproduce the correct two-point correlations in the filtered velocity field in LES is governed by its Karman-Howarth equation, and specifically whether the model correctly captures the two-point correlation functions between the stresses and the filtered strain-rates. Inspired by this statistical necessary condition, we develop a model that takes into account non-local effects by using fractional derivatives, and evaluate its performance using data from the Johns Hopkins Database (JHTDB). Starting from direct numerical simulation data of homogeneous isotropic turbulence and channel flows, we filter the data to separate the small and large scales, and calculate the two-point stress-strain rate correlations for the exact case and for models (a-priori) with different fractional orders. We observe that the Smagorinsky model based on standard gradients fails to produce the long range correlations observed in the exact case, while the fractional-gradient models capture the longer tails of the true correlations. As one approaches the wall in channel flow, more complex, highly anisotropic behavior is found. [Preview Abstract] |
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