Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D8: CFD: Turbulent Flows |
Hide Abstracts |
Chair: Giacomo Valerio Iungo, UT Dallas Room: 108 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D8.00001: Data-driven RANS for prediction of wind turbine wakes Giacomo Valerio Iungo, Francesco Viola, Umberto Ciri, Simone Camarri, Mario A. Rotea, Stefano Leonardi Wind turbine wakes are highly turbulent flows resulting from the interaction between the atmospheric boundary layer and wake vorticity structures. Measurement technologies, such as wind LiDARs, are currently available to perform velocity measurements in a set of locations of wakes past utility-scale wind turbines; however, computational methods are still needed to predict wake downstream evolution. In this work, a low-computational cost and accurate algorithm is proposed for prediction of the spatial evolution of wind turbine wakes. Reynolds-averaged Navier Stokes equations (RANS) are formulated in cylindrical coordinates and simplified by using a boundary layer type approximation. Turbulence effects are taken into account with a mixing length model calibrated on the available observations. In this study, observations of wind turbine wakes consist in LES data of wakes produced by a wind turbine operating with different incoming wind and loading conditions. The mixing length calibrated on the LES data is constant in the near wake and only affected by the incoming turbulence, whereas further downstream it increases roughly linearly with the downstream position and with increased slope for increasing rotational speed of the turbine. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D8.00002: Density Effects on the Shock-Turbulence Interaction Yifeng Tian, Farhad Jaberi, Daniel Livescu, Zhaorui Li High-order numerical simulations of isotropic multi-fluid turbulence interacting with a planar shock wave are performed using a hybrid numerical method, which combines a monotonicity-preserving scheme with a compact scheme. The main objective of this study is to investigate the effects of density variations due to compositional changes on the shock-turbulence interaction and mixing. Convergence tests are conducted to establish the accuracy of results using different meshes with a wide range of grid sizes inside and outside the shock zone. The computed statistics are found to be independent of the grid when the turbulence after the shock is well resolved and the scale separation between numerical shock thickness and turbulent scales is adequate. A reference simulation of single-fluid turbulence is also conducted with similar conditions. Compared to the single-fluid reference case, turbulence amplification by the normal shock wave is much higher and the reduction in turbulent length scales is much more significant in the presence of density variations due to compositional changes. Turbulent mixing enhancement by the shock wave is also more important in the multi-fluid case. The mechanisms behind multi-fluid shock-turbulence interaction and scalar mixing are identified by analyzing the transport equations for the Reynolds stress, vorticity and scalar variance. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D8.00003: Air entrainment due to shear-flow free surface turbulence Xiangming Yu, Dick K.P. Yue, Kelli Hendrickson We perform direct numerical simulations to study air entrainment at the air-water interface in three dimensional sheared turbulent flows with two-phase coupled at the free surface, using a two-phase conservative Volume-Of-Fluid (cVOF) method. For a given Reynolds number the problem is governed by the Froude number (Fr), above a threshold value of which air entrainment (AE) is observed. We consider a range of Fr and study the dependence on Fr of the volume V of AE, and the underlying air entraining structures and mechanisms of the interface. We determine the scaling of V with Fr and identify two key mechanisms for AE characterized respectively by surface-parallel vorticity and wave breaking. The former is associated with rising lambda vortices and strong near-surface horizontal vorticity, while the latter can be quantified by the decrease in potential energy of the interface. We propose models parameterized on Fr and the local turbulent flow properties that predict the AE volume associated with each of these mechanisms. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D8.00004: Minimum-dissipation models for large-eddy simulation Hyunji Jane Bae, Wybe Rozema, Parviz Moin, Roel Verstappen Minimum-dissipation eddy-viscosity models are a class of subgrid scale models for LES that give the minimum eddy dissipation required to dissipate the energy of subgrid scales. The QR minimum-dissipation model [Verstappen, J. Sci. Comp., 2011] gives good results in simulations of decaying grid turbulence carried out on an isotropic grid. In particular, due to the minimum dissipation property of the model, the predicted energy spectra are in very good agreement with the DNS results up to the cut-off wave number unlike other methods. However, its results on anisotropic grids are often unsatisfactory because the model does not properly incorporate the grid anisotropy. We propose the anisotropic minimum-dissipation (AMD) model [Rozema et. al., submitted for publication, 2015], a minimum-dissipation model that generalizes the QR model to anisotropic grids. The AMD model is more cost effective than the dynamic Smagorinsky model, appropriately switches off in laminar and transitional flow on anisotropic grids, and its subgrid scale model is consistent with the theoretic subgrid tensor. Experiments show that the AMD model is as accurate as the dynamic Smagorinsky model and Vreman model in simulations of isotropic turbulence, temporal mixing layer, and turbulent channel flow. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D8.00005: Error-measure for anisotropic grid-adaptation in turbulence-resolving simulations Siavash Toosi, Johan Larsson Grid-adaptation requires an error-measure that identifies where the grid should be refined. In the case of turbulence-resolving simulations (DES, LES, DNS), a simple error-measure is the small-scale resolved energy, which scales with both the modeled subgrid-stresses and the numerical truncation errors in many situations. Since this is a scalar measure, it does not carry any information on the anisotropy of the optimal grid-refinement. The purpose of this work is to introduce a new error-measure for turbulence-resolving simulations that is capable of predicting nearly-optimal anisotropic grids. Turbulent channel flow at $Re_\tau\approx 300$ is used to assess the performance of the proposed error-measure. The formulation is geometrically general, applicable to any type of unstructured grid. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D8.00006: Vortex Particle-Mesh methods for large scale LES of aircraft wakes Philippe Chatelain, Matthieu Duponcheel, Yves Marichal, Grégoire Winckelmans Vortex methods solve the NS equations in vorticity-velocity formulation. The present Particle-Mesh variant exploits the advantages of a hybrid approach: advection is handled by the particles while the mesh allows the evaluation of the differential operators and the use of fast Poisson solvers (here a Fourier-based solver which allows for unbounded directions and inlet/outlet boundaries). A lifting line approach models the vorticity sources in the flow; its immersed treatment efficiently captures the development of vorticity from thin sheets into 3-D field. Large scale simulations of aircraft wakes (including “encounter” cases where a following aircraft flies into the wake) are presented, which also demonstrate the performance of the methodology: the adequate treatment of particle distortion, the high-order discretization, and the multiscale subgrid models allow to capture wake dynamics with minimal spurious dispersion and diffusion. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D8.00007: Sensitivity Analysis of Chaotic Flow around Two-Dimensional Airfoil Patrick Blonigan, Qiqi Wang, Eric Nielsen, Boris Diskin Computational methods for sensitivity analysis are invaluable tools for fluid dynamics research and engineering design. These methods are used in many applications, including aerodynamic shape optimization and adaptive grid refinement. However, traditional sensitivity analysis methods, including the adjoint method, break down when applied to long-time averaged quantities in chaotic fluid flow fields, such as high-fidelity turbulence simulations. This break down is due to the ``Butterfly Effect''; the high sensitivity of chaotic dynamical systems to the initial condition. A new sensitivity analysis method developed by the authors, Least Squares Shadowing (LSS), can compute useful and accurate gradients for quantities of interest in chaotic dynamical systems. LSS computes gradients using the ``shadow trajectory'', a phase space trajectory (or solution) for which perturbations to the flow field do not grow exponentially in time. To efficiently compute many gradients for one objective function, we use an adjoint version of LSS. This talk will briefly outline Least Squares Shadowing and demonstrate it on chaotic flow around a Two-Dimensional airfoil. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D8.00008: Slow transition of the Osborne Reynolds pipe flow: A direct numerical simulation study. Xiaohua Wu, Parviz Moin, Ronald J. Adrian, Jon R. Baltzer Osborne Reynolds' pipe transition experiment marked the onset of fundamental turbulence research, yet the precise dynamics carrying the laminar state to fully-developed turbulence has been quite elusive. Our spatially-developing direct numerical simulation of this problem reveals interesting connections with theory and experiments. In particular, during transition the energy norms of localized, weakly finite inlet perturbations grow exponentially, rather than algebraically, with axial distance, in agreement with the edge-state based temporal results of Schneider et al (PRL, 034502, 2007). When inlet disturbance is the core region, helical vortex filaments evolve into large-scale reverse hairpin vortices. The interaction of these reverse hairpins among themselves or with the near-wall flow produces small-scale hairpin packets. When inlet disturbance is near the wall, optimally positioned quasi-spanwise structure is stretched into a Lambda vortex, which grows into a turbulent spot of concentrated small-scale hairpin vortices. Waves of hairpin-like structures were observed by Mullin (Ann. Rev. Fluid Mech., Vol.43, 2011) in their experiment with very weak blowing and suction. This vortex dynamics is broadly analogous to that in the boundary layer bypass transition and in the secondary instability and breakdown stage of natural transition. Further details of our simulation are reported in Wu et al (PNAS, 1509451112, 2015). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700