Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G41: CFD: General I |
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Chair: Vaibhav Joshi, University of British Columbia Room: 6c |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G41.00001: Mixing quantification in electromagnetically driven flow between concentric spheres Aldo Figueroa, Patrice Meunier The mixing quantification of a scalar in the gap of a two concentric spheres is studied theoretically. The flow is electromagnetically driven and is mainly rotational. The driving Lorentz force is generated by the interaction of a dc electric current radially injected in the equatorial zone and a dipolar magnetic field. A full three-dimensional numerical model was developed and has been calibrated with experimental velocity data. A new mixing protocol for high P\'eclet number has been developed. This method is based on the diffusive sheet method (Mart\'inez-Ruiz, Meunier, Favier \& Duchemin, J. Fluid Mech., vol. 837, 2018, pp. 230-257), which has been proven to be accurate in the mixing description of three-dimensional flows, however this new method is simpler and less time consuming. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G41.00002: Effect of Sweep Angle on the Hydrodynamic Characteristics of a Blended Wing Autonomous Underwater Glider using CFD Vijayakumar Rajagopalan, Mukesh Guggilla Underwater Gliders are unique buoyancy propelled oceanographic profiling vehicles. Their speed and endurance in longitudinal motion is affected by the symmetry, sweep, dihedral angle and span of the control surfaces. In low-velocity regime, these parameters can be varied to examine the flow around the glider. They also affect the lift-to-drag ratio (L/D) essential for the maneuvering path in longitudinal and transverse motions. In this paper, sweep angle (10$^{\mathrm{o}}$ to 60$^{\mathrm{o}}$ in steps of 5$^{\mathrm{o}})$ of the main wing is varied for a blended wing autonomous underwater glider and numerically simulated in the commercial software, STARCCM$+$. The main wing is a tapered NACA0018 section (as per the general arrangement requirement) with 1.5m chord at the root and 0.1m at the tip. The numerical model is validated using CFD results of NACA0012 airfoil from Sun.C et.al., 2015. The hydrodynamic forces are obtained by varying the angle of attack and side slip angles of the body from -20$^{\mathrm{o}}$ to 20$^{\mathrm{o}}$, for flow velocity of 0.4m/s. The lift-to-drag ratios, flow physics around the wing are analyzed and the trajectories are simulated (using in-house code) to arrive at an optimum L/D for increased endurance. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G41.00003: Modeling ventilation in an urban-slum home in Dhaka, Bangladesh Yunjae Hwang, Mahamudur Hasan, Laura Kwong, Fosiul Nizame, Stephen Luby, Catherine Gorle Improved ventilation in slum housing could reduce the incidence of pneumonia, which is the leading cause of death in children under five. The goal of this project is to assess the effectiveness of different ventilation strategies for low-income housing in Dhaka, Bangladesh. One of the main challenges identified in field experiments is the dependency of the ventilation pattern on both the configuration of the home, and on the highly variable operating conditions defined by weather and occupancy. In this study, we validate a computational framework with uncertainty quantification to predict ventilation rates in a representative slum home with different sizes and locations of openings. A low-fidelity model is used within a second-order probability framework: uncertainty due to inconsistent ventilation patterns is represented using both single-sided and cross-ventilation models, while uncertainty in model parameters is accounted for using Monte-Carlo simulation. The resulting predictions for the ventilation rate show a similar trend as the field measurements, but are subject to large uncertainty. In ongoing work, we are performing high-fidelity computational fluid dynamics simulations to investigate reducing the uncertainty in the low-fidelity model predictions. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G41.00004: Effect of detaching force on water retention on a surface Neda Ojaghlou, Dusan Bratko, Hooman V. Tafreshi, Alenka Luzar The interaction of droplets with a surface is crucial in engineering applications such as coating, air filtration, and liquid transport in microfluidic devices. Despite recent advances in fluid mechanics and surface science, the mechanism of droplet detachment from the surface and the amount of residue left behind are not formulated well. When the droplets are forcibly removed from a surface, the ease of detachment strongly depends on the droplet volume and the rate of the removal. Experiments and continuum level calculations have so far been unable to resolve the time-dependent dynamics of droplet detachment and the role of the applied force as the key determinant of the volume of the droplet residue on the surface. We present a comprehensive study for predicting the force required to detach the water droplet from a graphene surface through the Molecular Dynamics (MD) simulations. Our results show that the minimum detaching force (per unit mass) decreases with the volume of the droplet and increases with the strength of water-surface adhesion. We also determined the amount of residue on the surface after detachment for different forces and water-carbon interactions. We observed that as the droplet size increases, a bigger residue remains on the surface. We found that the maximum amount of residue can be observed by applying the minimum force of detachment in contrast to experimental and MD results for droplet detachment from the curved surfaces where intermediate force was found to maximize the water retention. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G41.00005: A reduced order model for prediction of aerodynamic loads on an unmanned aerial system with hybrid quadcopter biplane configuration Morteza Heydari, Hamid Sadat Army Research Lab (ARL) has recognized Unmanned Aerial Systems (UAS) with Vertical Take-Off and Landing (VTOL) to be capable of delivering paramount tasks such as intelligence, surveillance, electronic attack, etc. in the future. Advances in manufacturing and material technologies have opened a new design space for novel VTOL UAS configurations but significant knowledge gaps still exist to design a configuration which can achieve the desired performance. ARL designed research VTOL UAS platforms called Common Research Configuration (CRC) with hybrid quadcopter biplane concept to enable a comprehensive study on such aircraft. Inherent to all VTOL UAS such as CRC platforms is the need for a transition from hover to forward flight and forward flight back to hover throughout a mission. This transition produces highly non-linear loads on the wings due to the rotor-wing interactions and may present a significant challenge for robust control. The aim of this study is to develop a reduced order model (ROM) capable of predicting loads on CRC-3, the smallest size of the CRC generation with 3lb weight. A set of data obtained from hundreds of CFD simulations for a wide range of conditions are used as the training set for a neural network. The predicted loads by the developed ROM show good agreement with the test set. Additionally, the dynamic body equations are coupled with the ROM to investigate the CRC-3 flight dynamics. CFD simulations are conducted using our in-house solver, CFDFoam. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G41.00006: Simulation of three dimensional aeronautical flow using the SED-SL algebraic turbulence model. Tan-Tan Du, Meng-Juan Xiao, Wei-Tao Bi, Zhen-Su She The SED-SL model specifies a multilayered stress length (SL) function in the wall-normal direction (which depicts the eddy viscosity), with slowly varying parameters along the streamwise direction simulating the entire turbulent boundary layer (TBL) including transition. After successful simulations of transitional flat-plate (APS meeting, 2016), airfoils (APS meeting, 2017), and 3-D aeronautical flows (APS meeting, 2018), here we report an in-depth study of the SED-SL model in simulating flows over M6 wing and DLR-F4 wing-body. For the M6 wing, intuitive consideration suggests a mildly varying buffer layer thickness in the spanwise direction, yielding a more accurate prediction of the shock locations and their merging above the wing surface, and thus a better prediction of the aerodynamic forces than those of the SA and SST models. A comparison with a large eddy simulation of the flow shows also a superior prediction of the flow structures and Reynolds stress distribution. For the DLR-F4 wing-body, a significant improvement also is obtained with the new model compared to the SA and SST, in the prediction of the flow structures near the wing-body juncture and wing tip. These results demonstrate that the SED-SL model captures the right and simple (multilayer) structure of TBL, and is adaptable to aeronautic flows with not only high accuracy and efficiency for assisting design, but also more knowledge about the flow physics. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G41.00007: Computational Investigations of Flow Past Axially Aligned Rotating Cylinders Igbal Mehmedagic, Pasquale Carlucci, Liam Buckley, Donald Carlucci, Siva Thangam Projectiles with free spinning segments are often used in smart munitions to provide effective control, stability and target guidance. Computational investigations are performed for flow past cylinders aligned along their axis where either the middle or base segment freely spins while attached to a non-spinning fore and/or aft body. The energy spectrum is modified to incorporate the effects of swirl and rotation using a parametric characterization of the model coefficients. An efficient finite-volume algorithm is used to solve the time-averaged equations of motion along with the modeled form of transport equations for the turbulence kinetic energy and the scalar form of turbulence dissipation. Experimental data for a range of spin rates and free stream flow conditions obtained from subsonic wind tunnel for flow past axially aligned cylinders with spinning segments are used to validate the computational findings. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G41.00008: Optimization of Pressurized Water Reactor Size and Coolant Flow Rate Scott Wahlquist, Bryan Lewis In nuclear reactors, the heat generated in the system must be removed as fast as it is produced to operate in steady state. To accomplish this, liquid or gaseous coolant is moved through the core with pumps. In a typical pressurized water reactor (PWR), the standard inlet temperature is 290$^{\circ}$C and the standard outlet temperature is 325$^{\circ}$C. Using RANS modeling, a heat transfer CFD analysis was conducted on a basic structure of a PWR (neutron shield panel, nuclear core, and vessel wall) to show how water flows through the reactor and to determine the volumetric flow rate that creates the necessary convection to produce the inlet and outlet water temperature differential. The reactor was then scaled and the simulation was then repeated to observe the change in required flow rate. A plot comparing the size of the reactor to the required volumetric flow rate was made to determine the minimum and maximum reactors sizes with volumetric flow rates that don't exceed the max allowable flow rate of a typical PWR pump and still produces the outlet temperature. [Preview Abstract] |
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