Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D38: Large Eddy Simulations |
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Chair: Steven Miller, University of Florida Room: Georgia World Congress Center Ballroom 1/2 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D38.00001: A modified optimal LES model for highly compressible isotropic turbulence Chenyue Xie, Jianchun Wang, Hui Li, Minping Wan, Shiyi Chen An energy budget analysis and a posteriori tests of subgrid-scale (SGS) models for large eddy simulation (LES) of stationary highly compressible homogeneous isotropic turbulence are carried out at M_{t} ranging from 0.4 to 1.0 and Re_{λ} ranging from 180 to 250. An energy budget analysis shows that the SGS stress τ_{ij} and the SGS heat flux Q_{j} are dominant terms in the current M_{t} and Re_{λ} ranges, while other terms can be neglected in LES. We perform LES of compressible isotropic turbulence by using several SGS models including a DSM, a DMM, and an optimal model. In addition, a modified optimal model is constructed based on the magnitude of the filtered strain-rate tensor, inspired by the physical insight that the region of the large magnitude of the filtered strain-rate tensor plays a significant role in kinetic energy transfer. Spectra, statistics, and scaling of velocity and thermodynamic variables from LES are tested. The modified optimal model performs better than other models, especially for the spectrum of the compressible velocity component at relatively low M_{t} and high Re_{λ}. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D38.00002: On the Validation of a High-Order Large Eddy Simulation Solver for the Acoustic Prediction of Supersonic Jet Flow Weiqi Shen, Steven A E Miller A high-order large eddy simulation (LES) code based on the work of Stanford Aerospace Computing Laboratory called HiFiLES is further developed for supersonic jet flow simulation. The code uses a flux reconstruction method for spatial discretization and an explicit Runge-Kutta method for time advancement. LES with various subgrid scale models including static Smagorinsky, WALE, and similarity models are implemented. We implemented Persson’s shock detector with an exponential filter to capture discontinuities. A newly implemented Ffowcs-Williams and Hawkings acoustic solver is used for acoustic prediction. The acoustics solver relies on a new numerical probe technique to capture time histories of the flow-field variables. This numerical sampling technique is used for both acoustic prediction and flow-field validation. We validate our LES solver via examination of a supersonic off-design jet flow-field and acoustic data set from NASA Glenn Research Center. We present our modifications to the LES solver and validation results. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D38.00003: Some properties of a class of large eddy simulation turbulence models for incompressible magnetohydrodynamics David Sondak, John Shadid, Assad Oberai A new class of large eddy simulation turbulence models for incompressible magnetohydroynamics was developed in [1]. The new models were based upon the residual-based variational multiscale formulation. Tests on the decaying Taylor-Green vortex flow at various Reynolds numbers showed good results when compared to direct numerical simulations. The residual-based character of the models allows them to adapt to the flow physics. Moreover, the models are insensitive to model parameters. This property is demonstrated on three TG vortex flows each exhibiting a different energy spectrum. The new models, without any parameter tuning, are able to capture the correct inertial range behavior of each flow. Such adaptivity may be beneficial given the non-universality of MHD turbulence. Finally, under certain flow conditions, the models are able to capture a subgrid dynamo phenomenon in which an inverse energy cascade from unresolved velocity scales transfers energy to the resolved magnetic field.
[1] Sondak, D., Shadid, J.N., Oberai, A., Pawlowski, P., Cyr, E.C., Smith, T.M., A new class of finite element variational multiscale turbulence models for incompressible magnetohydrodynamics, Journal of Computational Physics 295, 596-616, 2015. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D38.00004: Simulating and investigating compressible flows interaction with fractal structures Omar Es-Sahli, Adrian Sescu, Mohammed Z. Afsar, and Oliver R.H. Buxton Omar Es-Sahli, Adrian Sescu, Mohammed Z Afsar, Oliver Buxton Previous experimental and numerical studies have investigated incompressible flow interactions with multi-scale fractal structures with the objective of generating turbulence at multiple scales. Depending on various flow conditions, it was found that these fractal structures are able to enhance mixing and scalar transport, and in some cases to contribute to the reduction of flow generated sound in certain frequency ranges. The interaction of compressible flows with multi-scale fractal structures did not receive much attention as the focus was entirely on the incompressible regime. The objective of this study is to conduct large eddy simulations of flow interactions with various fractal structures in the compressible regime and to extract and analyze different flow statistics in an attempt to determine the effect of compressibility. Immersed boundary methods will be employed to overcome the difficulty of modeling the fractal structures, with adequate mesh resolution around small features of the fractal shapes. |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D38.00005: Analysis of LES models in Stratified Flows Jeremy Melvin, Robert D Moser Hybrid RANS/LES (Reynolds Averaged Navier Stokes/Large Eddy Simulation) simulations of complex turbulent flows, such as those found in the simulation of wind farms, are reliant on the underlying physical assumptions of the RANS and LES models that are used in the hybridization. To improve the accuracy of these simulations, development of improved SGS (subgrid) models that perform well in the anisotropic turbulence found in stratified flows are desired. Through comparisons to data from direct numerical simulations (DNS) of stratified homogenous turbulence and benchmark LES simulations of stratified flows, we study the ability of various SGS models to accurately represent the flow dynamics. The importance of both the subgrid stress tensor and the subgrid scalar flux are investigated. With a focus on the use of a tensorial eddy viscosity, we discuss the path forward to a suitable LES model for hybrid simulations of wind farms. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D38.00006: LES of stratified turbulent shear flows at moderate to high Reynolds number Alexandra VanDine, Hieu T Pham, Sutanu Sarkar A large-eddy simulation (LES) model is used to study the evolution of stratified turbulence in two canonical problems: a temporally evolving shear layer and a spatially evolving wake. The presented LES model is adapted from that of Ducros et al. (1996). In the simulation of the shear layer at Reynolds number, Re = ΔUδ_{ω}/ν = 5,000, and bulk Richardson number, Ri_{b} = gΔρδ_{ω}/ρ_{0}ΔU^{2} = 0.1, the LES model successfully captures the evolution of Kelvin-Helmholtz rollers, the pairing of the rollers, and the generation of three-dimensional turbulence. The evolution of the momentum and density thickness, turbulent kinetic budget, and energy spectrum show excellent agreement with comparable direct numerical simulations (DNS). Simulations with the subgrid model at a high Re = 50,000 also yield good results. The LES model is also employed in the study of a spatially evolving wake at Re = U_{∞}D/ν = 3,700 and Froude number, Fr = U_{∞}/ND = 3, to demonstrate its ability to capture the development of coherent wake vortices, the evolution of wake dimensions, and defect velocity decay when compared to DNS results. We will also discuss the capability of the LES to simulate wakes at high Re and Fr. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D38.00007: A weak-shear correction to the Smagorinsky model for high-Reynolds-number wall-modelled simulations Johan Meyers, Bharathram Ganapathisubramani The Lilly-Smagorinsky model is known to work well in high-Reynolds HIT, but is too dissipative for wall-bounded flows. In wall-modelled LES, this leads to the log-layer mismatch and over prediction of streamwise velocity fluctuations. It has been shown that the mismatch is in part caused by the wall-stress model, but excluding this does not fully resolve the issue for the Smagorinsky model. Various heuristics exist to improve the model, e.g., based on wall damping, or the dynamic procedure, but theoretical insights into how the model coefficient should behave near the wall remain elusive. We show that, with increasing resolution, predictions of the Lilly-Smagorinsky model become very accurate away from the wall. However, when approaching the wall, an important aspect is the prediction of the subgrid mean shear. While the classical Lilly analysis links the coefficient to the Kolmogorov constant in inertial range turbulence, we show that this is not consistent with correct levels of subgrid mean shear in weak-shear turbulence. Based on generalizations of Lumley’s co-spectrum, we formulate a correction to the Smagorinsky model, that incorporates weak-shear effects. This solves the log-layer mismatch and leads to accurate predictions of the von Karman measure when compared to DNS. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D38.00008: Population Balance Modeling to study evolution of jet with polydisperse oil droplets in a Large Eddy Simulation framework Aditya Aiyer, Di Yang, Marcelo Chamecki, Charles Vivant Meneveau In the context of oil spills, knowledge of the dispersed phase droplet size distribution and its evolution is critical to predict many macroscopic features. We adopt a population dynamics model for polydisperse droplet size distributions in a Large Eddy Simulation framework. This allows us to study the evolution of the number density of droplets due to convection, breakup and coalescence. Modeling breakup based on turbulent fluctuations and collisions is a major mechanism that has been adopted in the literature, in which the breakup occurs primarily due to the bombardment of droplets by turbulent eddies. Existing models assume the scale of droplet-eddy collision to be in the inertial scale of turbulence. In this work we extend the breakup kernels to the entire spectrum of turbulence using generalized structure functions. As a flow application for LES we consider a jet in crossflow with oil being released at the source of the jet. We model the concentration fields of the droplets using an Eulerian approach. We compare the droplet size distribution obtained from our simulations with published experimental data. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D38.00009: An Eulerian large eddy simulation model of deep-sea oil/gas plumes with gas dissolution effect Chen Peng, Marcelo Chamecki, Charles Meneveau, Di Yang During a deep-sea oil wellhead blowout accident, the oil/gas mixed plume rises through the ocean driven by the buoyancy induced by gas bubbles. As the plume rises, it continuously loses its driving force as gas bubbles are dissolved by the ambient sea water. Accurately modeling the effect of gas dissolution is thus crucial for understanding plume dynamics and predicting the oil dispersion, which are key pieces of information needed for planning oil spill remediation. In this study, a fast Eulerian large-eddy simulation (LES) approach is used to model the effect of gas dissolution on plume dynamics. By simultaneously simulating the evolutions of the bubble mass concentration function and the number density field, the average bubble size in each LES computational cell can be calculated locally. Based on this information, the local gas dissolution rate and bubble rise velocity are computed, which are then used in the gas transport equations. This fast Eulerian LES model can capture the effect of gas bubble dissolution on the macroscopic plume characteristics with reasonable computational cost. In this talk, some preliminary results for LES of deep-sea hydrocarbon plume blowout are presented. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D38.00010: Large eddy simulation of bubble-driven plume with finite bubble void fraction Shuolin Xiao, Di Yang Eulerian-Eulerian large eddy simulation (LES) approach is widely used for modeling bubble-driven plumes in many environmental and industrial applications. Under low bubble void fraction condition, bubbles can be treated as a dispersed phase for which an Eulerian transport equation is solved to compute the evolution of bubble concentration in the turbulence flow, and effect of bubbles on the flow field is added to the momentum equation through a buoyancy force term. This allows fast computation of the plume evolution by avoiding significant modification to the flow solver. However, under many practical conditions the bubble void fraction is not negligible, requiring additional modifications to the flow solver to account for other effects due to finite bubble void fraction. In this study, an LES model for bubble-driven plume with finite void fraction is developed. Preliminary tests for lab-scale cases are conducted and compared with those obtained from an LES model with low-void-fraction approximation. The new model is shown to efficiently capture the effect of non-negligible bubble void fraction on plume characteristics without significantly increasing the computational cost. |
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