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 L6: CFD: Applications I |
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Chair: Chris Rycroft, Harvard University Room: 105 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L6.00001: How does network design constrain optimal operation of intermittent water supply? Anna Lieb, Jon Wilkening, Chris Rycroft Urban water distribution systems do not always supply water continuously or reliably. As pipes fill and empty, pressure transients may contribute to degraded infrastructure and poor water quality. To help understand and manage this undesirable side effect of intermittent water supply---a phenomenon affecting hundreds of millions of people in cities around the world---we study the relative contributions of fixed versus dynamic properties of the network. Using a dynamical model of unsteady transition pipe flow, we study how different elements of network design, such as network geometry, pipe material, and pipe slope, contribute to undesirable pressure transients. Using an optimization framework, we then investigate to what extent network operation decisions such as supply timing and inflow rate may mitigate these effects. We characterize some aspects of network design that make them more or less amenable to operational optimization. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L6.00002: Defining boundary conditions for RANS predictions of urban flows using mesoscale simulations Clara Garcia Sanchez, Catherine Gorle, Jeroen van Beeck Pollutant dispersion and wind flows in urban canopies are major concerns for human health and energy, and the complex nature of the flow and transport processes remains a challenge when using Computational Fluid Dynamics (CFD) to predict wind flows. The definition of the inflow boundary condition in Reynolds-Averaged Navier-Stokes simulations (RANS) is one of the uncertainties that will strongly influence the prediction of the flow field, and thus, the dispersion pattern. The goal of the work presented is to define a methodology that improves the level of realism in the inflow condition for RANS simulations by accounting for larger mesoscale effects. The Weather Research and Forecasting model (WRF) is used to forecast mesoscale flow patterns, and two different approaches are used to define inflow conditions for the RANS simulations performed with OpenFOAM: 1) WRF variables such as local velocity magnitude, ABL height and friction velocity are directly interpolated onto the boundaries of the CFD domain; 2) WRF predictions for the geostrophic wind and friction velocity are applied as a forcing boundary condition. Simulations of the Joint Urban 2003 experimental campaign in Oklahoma City have been performed using both approaches and a comparison of the results will be presented. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L6.00003: Numerical Study of Wind Shielding Impacts on Water Quality in a Tropical Urban Lake Haiyan Miao, Zikun Xing, Lloyd Chua In this study, we investigate the impact of wind shielding effect on hydrodynamics and water quality in Marina reservoir, a tropical lake located in downtown Singapore. This kind of urban lakes are usually smaller and shallower comparing with naturally formed ones and therefore, subject to a higher degree of interaction with wind. To establish wind field over the lake surface, Computational Fluid Dynamics (CFD) modeling was conducted to simulate seasonal impacts of two dominant monsoon seasons, in which the prevailing wind patterns interact very differently with urban landscape. The CFD model results were then used as input to a 3D lake hydrodynamics and water quality model to study the impacts to the hydrodynamics and water quality in the lake. By comparing simulations using uniform and spatial variable wind field, this study demonstrates that wind forcing variability in urban reservoirs that arise from shielding effects can have significant impacts on the thermal stratification and mixing, and phytoplankton distribution in both vertical and horizontal directions. There exist significant seasonal differences in wind field, hydrodynamics and water quality between the northeast and southwest monsoon seasons. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L6.00004: SimVascular 2.0: an Integrated Open Source Pipeline for Image-Based Cardiovascular Modeling and Simulation Hongzhi Lan, Jameson Merkow, Adam Updegrove, Daniele Schiavazzi, Nathan Wilson, Shawn Shadden, Alison Marsden SimVascular (www.simvascular.org) is currently the only fully open source software package that provides a complete pipeline from medical image based modeling to patient specific blood flow simulation and analysis. It was initially released in 2007 and has contributed to numerous advances in fundamental hemodynamics research, surgical planning, and medical device design. However, early versions had several major barriers preventing wider adoption by new users, large-scale application in clinical and research studies, and educational access. In the past years, SimVascular 2.0 has made significant progress by integrating open source alternatives for the expensive commercial libraries previously required for anatomic modeling, mesh generation and the linear solver. In addition, it simplified the across-platform compilation process, improved the graphical user interface and launched a comprehensive documentation website. Many enhancements and new features have been incorporated for the whole pipeline, such as 3-D segmentation, Boolean operation for discrete triangulated surfaces, and multi-scale coupling for closed loop boundary conditions. In this presentation we will briefly overview the modeling/simulation pipeline and advances of the new SimVascular 2.0. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L6.00005: Flapping dynamics of an inverted flag in a uniform flow Jaeha Ryu, Sung Goon Park, Boyoung Kim, Hyung Jin Sung Much research in recent years has focused on the flow dynamics of flexible structures in a uniform flow and particularly on the flow dynamics related to energy harvesting systems. An energy harvesting system comprising piezoelectric patches attached to the surface of a flexible structure can convert the energy stored in solid deformations into an electric current that powers a purely resistive output circuit. Recently, an inverted flag which has the freely moving leading edge and the clamped trailing edge was suggested. The inverted flag improved the amount of strain energy that was converted into the flag deformations from the surrounding fluid. In this study, the flapping dynamics of an inverted flag in a uniform flow were simulated using the immersed boundary method. The flapping dynamics of and vortical structures around the inverted flag were examined in terms of the bending rigidity and the Reynolds number. The strain energy of the inverted flag and the proportion of the strain energy of the inverted flag to the kinetic energy of the flow were considered as an indicator of the energy harvesting system efficiency. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L6.00006: ABSTRACT WITHDRAWN |
Monday, November 23, 2015 5:23PM - 5:36PM |
L6.00007: Numerical simulation of artificial and natural rough surfaces Robin Andersson, Patrik Andreasson, Gunnar Hellstr\"om, Anders Andersson Flow in hydraulic tunnels is characterized by high velocities, non-uniform and fluctuating distributions of pressure and velocity. Pressure fluctuations may in the long run lead to unwanted effects such as erosion and in extreme cases the complete collapse of a tunnel. Natural rough surfaces, such as in hydropower tunnels, typically have the property of self-similarity. When observing the surfaces from a far, a large scale roughness is visible, but when observed from a very short distance a similar pattern of surface roughness can be observed. One procedure when evaluating flow over rough surfaces is to account for the large scale roughness and replace the small scale roughness with numerical wall functions, the self-similarity is excluded and is replaced by a numerical shear stress. The objective for this work is to gain a deeper understanding the impact that the small scale roughness has on the flow. In this work simulations where performed on a rough surface from a laser scanned hydropower tunnel, the simulation was then compared with an artificially generated rough surface. The reported results include evaluation and comparison of the friction velocity and Reynolds-stresses. Also, a characteristic roughness length scale $k_{s}$ is evaluated from the logarithmic law of the wall. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L6.00008: Numerical modelling of microdroplet self-propelled jumping on micro-textured surface S. M. Reza Attarzadeh, Ali Dolatabadi, Kyung Chun Kim Understanding various stages of single and multiple droplet impact on a super-hydrophobic surface is of interest for many industrial applications such as aerospace industry. In this study, the phenomenon of coalescence induced droplets self-propelled jumping on a micro-textured super-hydrophobic surface is numerically simulated using Volume of Fluid (VOF) method. This model mimics the scenario of coalescing cloud-sized particles over the surface structure of an aircraft. The VOF coupled with a dynamic contact angle model is used to simulate the coalescence of two equal size droplets, that are initially placed very closed to each other with their interface overlapping with each other's which triggers the incipience of their coalescence. The textured surface is modeled as a series of equally spaced squared pillars, with 111$^{\circ}$ as the intrinsic contact angle all over the solid contact area. It is shown that the radial velocity of coalescing liquid bridge is reverted to upward direction due to the counter action of the surface to the basal area of droplet in contact. The presence of air beneath the droplet inside micro grooves which aimed at repelling water droplet is also captured in this model. The simulated results are found in good agreement with experimental observations. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L6.00009: A New Simulation Framework for the Natural Convection in Practical Products ChungGang Li, Tsubokura Makoto Natural convection is one of the most major heat transfer methods in practical products owing to its cost effectiveness. This kind of topic accompanies with several critical issues including the high temperature difference, rapid turnaround and complex geometry. The present program adopts all-speed preconditioned Roe (A-P-Roe) to solve low speed compressible flows caused by natural convection. Besides, Building Cube Method (BCM) with a new interpolation method for the immersed boundary is utilized to increase the turnaround speed and handle complex geometry. The results show that the present program can be adopted in massively parallel systems such as ExaFlops computers because of good strong scaling test and is suitable for designing and analyzing products due to its high performance and wide availability. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L6.00010: Understanding vapour plume structure in indoor environments for the detection of explosives Tim Foat Dogs remain the most effective method for the detection of explosives in many situations yet the spatially, temporally and chemically varying signature that they sense cannot easily be quantified. Vapour plumes can be highly unsteady and intermittent and the problem is further complicated in indoor spaces where turbulent, transitional and laminar regions may exist and where there may be no dominant flow direction. Intermittent plumes can have peak concentrations that are considerably higher than the time averaged values. As dogs can sample the air at 5 Hz it is possible that these unsteady fluctuations play a key part in their detection process. A low Reynolds number (Re less than 5000 at the inlet) benchmark test case for indoor airflow has been studied using large-eddy simulation computational fluid dynamics. Fixed concentration vapour sources have been included on the floor of the room and the resulting vapour dispersion has been modelled. Sources with different surface areas have been included and their instantaneous and mean concentration profiles compared. The results from this study will provide insight into canine detection of vapour in indoor environments. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L6.00011: ABSTRACT WITHDRAWN |
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