Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session G31: CFD: Applications |
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Chair: Andy Nonaka, Lawrence Berkely National Laboratory Room: 2018 |
Monday, November 24, 2014 8:00AM - 8:13AM |
G31.00001: CFD Aided Design and Production of Hydraulic Turbines Alper Kaplan, Huseyin Cetinturk, Gizem Demirel, Ece Ayli, Kutay Celebioglu, Selin Aradag Hydraulic turbines are turbo machines which produce electricity from hydraulic energy. Francis type turbines are the most common one in use today. The design of these turbines requires high engineering effort since each turbine is tailor made due to different head and discharge. Therefore each component of the turbine is designed specifically. During the last decades, Computational Fluid Dynamics (CFD) has become very useful tool to predict hydraulic machinery performance and save time and money for designers. This paper describes a design methodology to optimize a Francis turbine by integrating theoretical and experimental fundamentals of hydraulic machines and commercial CFD codes. Specific turbines are designed and manufactured with the help of a collaborative CFD/CAD/CAM methodology based on computational fluid dynamics and five-axis machining for hydraulic electric power plants. The details are presented in this study. [Preview Abstract] |
Monday, November 24, 2014 8:13AM - 8:26AM |
G31.00002: Application of Computational Fluid Dynamics Model to Disinfection Reactors in Water Reclamation Plants Andrea Helmns, Pablo Texeira, Emin Issakhanian, Jose Saez California's current drought has renewed public interest in recycled water from Water Reclamation Plants (WRPs). It is critical that the recycled water meets public health standards. This project consists of simulating the transport of an instantaneous conservative tracer through the chlorine contact tanks at two WRPs in California, where recycled water regulations stipulate a minimum 90-minute modal contact time during disinfection at peak dry weather design flow. Computational Fluid Dynamics (CFD) is used to model the turbulent flow, transport, and contact time of a conservative solute for several real operating scenarios. Given as-built drawings and operation parameters, the chlorine contact tanks are modeled to match actual geometries and flow conditions. The turbulent flow solutions are~used as the basis to model the transport of a turbulently diffusing~conservative tracer added instantaneously to the inlet of the reactors. This tracer simulates~the transport through advection and dispersion of chlorine in the WRPs. Breakthrough curves of the tracer at the outlet are used to determine the modal contact times. [Preview Abstract] |
Monday, November 24, 2014 8:26AM - 8:39AM |
G31.00003: Large-eddy simulation of turbulent flows around a fin-tube heat exchanger enclosed by a compartment Changkeun Son, Simon Song, Jeesoo Lee, Seongwon Kang The main objective of the present study is to analyze heat transfer and flow characteristics of a heat exchanger in an industrial application using high-fidelity simulation techniques. Large-eddy simulations (LES) were performed to investigate the turbulent flows around a fin-tube heat exchanger enclosed by a compartment. The complex geometry of the compartment poses a difficulty in a simulation as the local Re number is about two orders of different magnitude, and generates various scales of the 3-D vortices and complex flow patterns. Careful tests with both grid resolution and turbulent inflow boundary condition were performed in order to compare our results to the measured data from a MRV experiment as well as the results from RANS simulations. From interaction of the flow structures such as the 3-D vortices, a few interesting flow phenomena were observed which are different from a plain fin-tube heat exchanger, such as helical flows and a jet stream observed behind the fin-tube region. Also, performance of the heat exchanger was analyzed using the data from plain fin-tube heat exchangers. Based on this analysis, a numerical technique for heat exchanger was devised and tested to show a possibility of reducing the computational cost significantly, using a porous media model. [Preview Abstract] |
Monday, November 24, 2014 8:39AM - 8:52AM |
G31.00004: Control of Flow Structure in Square Cross-Sectioned U Bend using Numerical Modeling Mehmet Metin Yavuz, Yigitcan Guden Due to the curvature in U-bends, the flow development involves complex flow structures including Dean vortices and high levels of turbulence that are quite critical in considering noise problems and structural failure of the ducts. Computational fluid dynamic (CFD) models are developed using ANSYS Fluent to analyze and to control the flow structure in a square cross-sectioned U-bend with a radius of curvature R$_{\mathrm{c}}$/D$=$0.65. The predictions of velocity profiles on different angular positions of the U-bend are compared against the experimental results available in the literature and the previous numerical studies. The performances of different turbulence models are evaluated to propose the best numerical approach that has high accuracy with reduced computation time. The numerical results of the present study indicate improvements with respect to the previous numerical predictions and very good agreement with the available experimental results. In addition, a flow control technique is utilized to regulate the flow inside the bend. The elimination of Dean vortices along with significant reduction in turbulence levels in different cross flow planes are successfully achieved when the flow control technique is applied. [Preview Abstract] |
Monday, November 24, 2014 8:52AM - 9:05AM |
G31.00005: Development of an Open Source Image-Based Flow Modeling Software - SimVascular Adam Updegrove, Jameson Merkow, Daniele Schiavazzi, Nathan Wilson, Alison Marsden, Shawn Shadden SimVascular (www.simvascular.org) is currently the only comprehensive software package that provides a complete pipeline from medical image data segmentation to patient specific blood flow simulation. This software and its derivatives have been used in hundreds of conference abstracts and peer-reviewed journal articles, as well as the foundation of medical startups. SimVascular was initially released in August 2007, yet major challenges and deterrents for new adopters were the requirement of licensing three expensive commercial libraries utilized by the software, a complicated build process, and a lack of documentation, support and organized maintenance. In the past year, the SimVascular team has made significant progress to integrate open source alternatives for the linear solver, solid modeling, and mesh generation commercial libraries required by the original public release. In addition, the build system, available distributions, and graphical user interface have been significantly enhanced. Finally, the software has been updated to enable users to directly run simulations using models and boundary condition values, included in the Vascular Model Repository (vascularmodel.org). In this presentation we will briefly overview the capabilities of the new SimVascular 2.0 release. [Preview Abstract] |
Monday, November 24, 2014 9:05AM - 9:18AM |
G31.00006: Effect of Flow Rate Controller on Liquid Steel Flow in Continuous Casting Mold using Numerical Modeling Kadir Ali Gursoy, Mehmet Metin Yavuz In continuous casting operation of steel, the flow through tundish to the mold can be controlled by different flow rate control systems including stopper rod and slide-gate. Ladle changes in continuous casting machines result in liquid steel level changes in tundishes. During this transient event of production, the flow rate controller opening is increased to reduce the pressure drop across the opening which helps to keep the mass flow rate at the desired level for the reduced liquid steel level in tundish. In the present study, computational fluid dynamic (CFD) models are developed to investigate the effect of flow rate controller on mold flow structure, and particularly to understand the effect of flow controller opening on meniscus flow. First, a detailed validation of the CFD models is conducted using available experimental data and the performances of different turbulence models are compared. Then, the constant throughput casting operations for different flow rate controller openings are simulated to quantify the opening effect on meniscus region. The results indicate that the meniscus velocities are significantly affected by the flow rate controller and its opening level. The steady state operations, specified as constant throughput casting, do not provide the same mold flow if the controller opening is altered. Thus, for quality and castability purposes, adjusting the flow controller opening to obtain the fixed mold flow structure is proposed. [Preview Abstract] |
Monday, November 24, 2014 9:18AM - 9:31AM |
G31.00007: Geometric VOF-PLIC simulations of Hollow Cone Sprays Thomas Nelson, Michael Benson, Brett VanPoppel, Luis Bravo This work examines a Computational Fluid Dynamics (CFD) approach to provide temporally resolved simulations of a novel pressure swirl atomizer presently studied at Stanford University [1]. In a pressure swirl atomizer, the liquid spreads out to form an air-cored vortex within the nozzle and an emerging thin annular film. Due to instabilities the film breaks up to form a hollow cone spray. The numerical simulations focus on the near field nozzle flow physics and primary atomization of the spray. An incompressible flow formulation is adopted with a geometric unsplit Volume of Fluid (VOF) method to track the interface between two immiscible fluids in interfacial flow simulations. Here, the interface is modeled via an advection equation implicitly tracked using a discrete indicator function, f, with values representing the volume fraction of the tagged fluid within a cell. An Adaptive Mesh Refinement (AMR) scheme is also employed to efficiently capture the shear layers near the liquid-gas interface. The study is carried out for two atomizers with 2mm and 3mm diameters at intermediate Re $=$ 2.6-3.9x103, We$=$0.11-0.17x105. An in depth comparison is then provided between the CFD results and measurements obtained via shadowgraphy and CT scans.\\[4pt] [1] P.A. Vazques, J. Eaton, R. Fahrig, et al, ILASS, 2014. [Preview Abstract] |
Monday, November 24, 2014 9:31AM - 9:44AM |
G31.00008: Supercritical fluid mixing in Diesel Engine Applications Luis Bravo, Peter Ma, Matthew Kurman, Michael Tess, Matthias Ihme, Chol-Bum Kweon A numerical framework for simulating supercritical fluids mixing with large density ratios is presented in the context of diesel sprays. Accurate modeling of real fluid effects on the fuel air mixture formation process is critical in characterizing engine combustion. Recent work (Dahms, 2013) has suggested that liquid fuel enters the chamber in a transcritical state and rapidly evolves to supercritical regime where the interface transitions from a distinct liquid/gas interface into a continuous turbulent mixing layer. In this work, the Peng Robinson EoS is invoked as the real fluid model due to an acceptable compromise between accuracy and computational tractability. Measurements at supercritical conditions are reported from the Constant Pressure Flow (CPF) chamber facility at the Army Research Laboratory. Mie and Schlieren optical spray diagnostics are utilized to provide time resolved liquid and vapor penetration length measurement. The quantitative comparison presented is discussed. [Preview Abstract] |
Monday, November 24, 2014 9:44AM - 9:57AM |
G31.00009: An Evaluation of a Phase-Lag Boundary Condition for Francis Hydroturbine Simulations Using a Pressure-Based Solver Alex Wouden, John Cimbala, Bryan Lewis While the periodic boundary condition is useful for handling rotational symmetry in many axisymmetric geometries, its application fails for analysis of rotor-stator interaction (RSI) in multi-stage turbomachinery flow. The inadequacy arises from the underlying geometry where the blade counts per row differ, since the blade counts are crafted to deter the destructive harmonic forces of synchronous blade passing. Therefore, to achieve the computational advantage of modeling a single blade passage per row while preserving the integrity of the RSI, a phase-lag boundary condition is adapted to OpenFOAM\textsuperscript{\textregistered{}} software's incompressible pressure-based solver. The phase-lag construct is accomplished through restating the implicit periodic boundary condition as a constant boundary condition that is updated at each time step with phase-shifted data from the coupled cells adjacent to the boundary. Its effectiveness is demonstrated using a typical Francis hydroturbine modeled as single- and double-passages with phase-lag boundary conditions. The evaluation of the phase-lag condition is based on the correspondence of the overall computational performance and the calculated flow parameters of the phase-lag simulations with those of a baseline full-wheel simulation. [Preview Abstract] |
Monday, November 24, 2014 9:57AM - 10:10AM |
G31.00010: About the prediction of Organic Rankine Cycles performances integrating local high-fidelity turbines simulation and uncertainties Pietro Congedo, Dante De Santis, Gianluca Geraci Organic Rankine Cycles (ORCs) are of key-importance when exploiting energy systems with a high efficiency. The variability of renewable heat sources makes more complex the global performance prediction of a cycle. The thermodynamic properties of the complex fluids used in the process are another source of uncertainty. The need for a predictive and robust simulation tool of ORCs remains strong. A high-order accurate Residual Distribution scheme has been recently developed for efficiently computing a turbine stage on unstructured grids, including advanced equations of state in order to take into account the complex fluids used in ORCs. Advantages in using high-order methods have been highlighted, in terms of number of degrees of freedom and computational time used, for computing the numerical solution with a greater accuracy compared to lower-order methods, even for shocked flows. The objective of this work is to quantify the numerical error with respect to the various sources of uncertainty of the ORC turbine, thus providing a very high-fidelity prediction in the coupled physical/stochastic space. [Preview Abstract] |
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