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 R6: CFD: General |
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Chair: Sandra Sowah, Princeton University Room: 105 |
Tuesday, November 24, 2015 12:50PM - 1:03PM |
R6.00001: Numerical Simulations of Curvature Effects in Laminar Channel Flows Sandra S. Sowah, Michael E. Mueller, Howard A. Stone Numerical simulations of curvature effects in laminar channel flows are performed by introducing body force terms into the Navier-Stokes equations, which are written in Cartesian coordinates. The advantage of introducing body force terms within a Cartesian framework, compared to performing simulations in native cylindrical coordinates, is the ability to easily transition from straight to curved regions of a channel flow. Using this approach, the onset of Dean vortices for laminar flow is investigated for varying Reynolds numbers and ratios of radius of curvature to channel height. The results are verified against simulations in cylindrical coordinates. [Preview Abstract] |
Tuesday, November 24, 2015 1:03PM - 1:16PM |
R6.00002: An Eulerian-based Bubble Dynamics Model for Computational Fluid Dynamics Asish Balu, Michael Kinzel Cavitation dynamics of nuclei are largely governed by the Rayleigh-Plesset Equation (RPE). This research explores the implementation of a one-way coupling to the solution of the RPE to a computational fluid dynamics (CFD) simulation in an Eulerian-framework. In this work, we used transport equations (i.e., advection) of the bubble radius and bubble growth rate, both of which are governed by advection mechanisms and coupling to the RPE through the CFD pressure field. The method is validated in the context of hypothetical pressure fields by prescribing a temporally varying pressure. Then, it is extended to one-way coupling with cavitation development in three different flow situations: (1) flow over a cylinder, (2) bubble formation during a bottle collapse event, and (3) cavitation in a tip vortex. In the context of these flows, the CFD simulations replicate an equivalent MATLAB-based solution to the RPE, thus validating the model. Additionally, an analytical formulation for appropriate upper and lower bounds for the bubble's physical properties is presented. These boundary values allow the CFD solver to run at larger time steps, therefore increasing the rate of convergence as well as maintaining solution accuracy. The results from this work suggest that Eulerian-based RPE cavitation models are practical and have the potential to simulate large numbers of bubbles that challenge Lagrangian methods. [Preview Abstract] |
Tuesday, November 24, 2015 1:16PM - 1:29PM |
R6.00003: ABSTRACT WITHDRAWN |
Tuesday, November 24, 2015 1:29PM - 1:42PM |
R6.00004: Aiding Design of Wave Energy Converters via Computational Simulations Hejar Jebeli Aqdam, Babak Ahmadi, Mehdi Raessi, Mazdak Tootkaboni With the increasing interest in renewable energy sources, wave energy converters will continue to gain attention as a viable alternative to current electricity production methods. It is therefore crucial to develop computational tools for the design and analysis of wave energy converters. A successful design requires balance between the design performance and cost. Here an analytical solution is used for the approximate analysis of interactions between a flap-type wave energy converter (WEC) and waves. The method is verified using other flow solvers and experimental test cases. Then the model is used in conjunction with a powerful heuristic optimization engine, Charged System Search (CSS) to explore the WEC design space. CSS is inspired by charged particles behavior. It searches the design space by considering candidate answers as charged particles and moving them based on the Coulomb's laws of electrostatics and Newton's laws of motion to find the global optimum. Finally the impacts of changes in different design parameters on the power takeout of the superior WEC designs are investigated. [Preview Abstract] |
Tuesday, November 24, 2015 1:42PM - 1:55PM |
R6.00005: An Assessment of Supercavitation Transition using Computational Fluid Dynamics Melissa Fronzeo, Michael Kinzel A computational fluid dynamics approach is used to improve the understanding of supercavitation and its physical characteristics. A ventilated disk cavitator is used in several studies to evaluate these physics. The first study focuses on twin vortex cavities, specifically to understand correlation between cavity shape and pressure. The study uses validated measurements (in the CFD model) of the cavity shape and pressure for various ventilation rates and Fr numbers. The data is used to evaluate the semi-empirical formula of L.A Epstein, where results indicate a potentially improved correlation. In addition, the detailed measurements of the CFD model yield insight on improved experimental measurement techniques for cavity pressure. The second study uses unsteady detached eddy simulations (DES) to predict hysteresis in the transition behavior of the cavity closure from toroidal vortex to twin-vortex regimes. The solution is initialized as a toroidal-type cavity (low gas ventilation rate), then the ventilation rate is slowly increased until a twin-vortex cavity is formed. In addition, the opposite process is also performed. The data is analyzed to develop an understanding of the unknown physical mechanisms involved in the transition process. [Preview Abstract] |
Tuesday, November 24, 2015 1:55PM - 2:08PM |
R6.00006: The Immersed Interface Method for Flow Around Non-Smooth Boundaries. Yang Liu, Sheng Xu In the immersed interface method, a boundary immersed in a fluid is generated by a singular force in the Navier-Stokes equations, and the singular force enters a numerical scheme as jump conditions across the boundary. In previous work, the method has been developed for smooth boundaries. In this talk, we present how to extend the method for non-smooth boundaries. We use panels to represent a boundary, compute necessary jump conditions explicitly, and compare two different pressure Poisson solvers. We test our extended method by simulating flows past a circular cylinder, a square cylinder or around a flapping plate. Our results show that the method is robust, accurate and efficient. [Preview Abstract] |
Tuesday, November 24, 2015 2:08PM - 2:21PM |
R6.00007: Computational Framework for a Fully-Coupled, Collocated-Arrangement Flow Solver Applicable at all Speeds Cheng-Nian XIao, Fabian Denner, Berend van Wachem A pressure-based Navier-Stokes solver which is applicable to fluid flow problems of a wide range of speeds is presented. The novel solver is based on collocated variable arrangement and uses a modified Rhie-Chow interpolation method to assure implicit pressure-velocity coupling. A Mach number biased modification to the continuity equation as well as coupling of flow and thermodynamic variables via an energy equation and equation of state enable the simulation of compressible flows belonging to transonic or supersonic Mach number regimes. The flow equation systems are all solved simultaneously, thus guaranteeing strong coupling between pressure and velocity at each iteration step. Shock-capturing is accomplished via nonlinear spatial discretisation schemes which adaptively apply an appropriate blending of first-order upwind and second-order central schemes depending on the local smoothness of the flow field. A selection of standard test problems will be presented to demonstrate the solver’s capability of handling incompressible as well as compressible flow fields of vastly different speed regimes on structured as well as unstructured meshes. [Preview Abstract] |
Tuesday, November 24, 2015 2:21PM - 2:34PM |
R6.00008: Lagrangian Proper Orthogonal Decomposition of the Wake Downstream of a Cylinder Jack Rossetti, Melissa Green, John Dannenhoffer Proper orthogonal decomposition (POD) has long been utilized by the fluid dynamics community to extract information regarding the energy contained in the structures of turbulent flows. These POD techniques are generally executed in an Eulerian frame, encapsulating all the structures created and destroyed through time. Unfortunately, the mode shapes that Eulerian POD produce are linked to the translation of structures and little is learned about the evolution of individual structures. We overcome this by applying POD in a Lagrangian frame. We first track pertinent features through cross-correlation techniques. Both Eulerian and Lagrangian POD were tested on a CFD simulation of the wake downstream of a cylinder. Eulerian POD focuses on the large-scale von Karman vortex street, whereas the Lagrangian POD allows one to extract physical phenomena associated with each of the individual vortices. This can result in a better understanding of the physics within each vortex. [Preview Abstract] |
Tuesday, November 24, 2015 2:34PM - 2:47PM |
R6.00009: ABSTRACT WITHDRAWN |
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