Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session F31: General Computational Fluid Dynamics |
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Chair: Christopher Rycroft, Harvard University Room: Georgia World Congress Center B403 |
Monday, November 19, 2018 8:00AM - 8:13AM |
F31.00001: The reference map technique for incompressible fluid--structure interaction problems Chris H. Rycroft, Yuexia Lin, Nicholas Derr, Kenneth Kamrin This talk will introduce the reference map technique, a fully Eulerian approach to simulate soft structures immersed in an incompressible fluid. The flow is simulated on a fixed grid using a second-order projection method to solve the incompressible Navier--Stokes equations. By introducing a reference map variable to model finite-deformation constitutive relations in the structure on the same grid as the fluid, the interfacial coupling problem is highly simplified. The technique is a computationally efficient alternative to moving mesh approaches, and example simulations featuring many-body contacts and flexible swimmers will be presented. |
Monday, November 19, 2018 8:13AM - 8:26AM |
F31.00002: An Eulerian method for mixed soft and rigid body interactions in fluids Xiaolin Wang, Kenneth N Kamrin, Christopher Rycroft Fluid-solid interaction problems are encountered in many engineering and biological applications, but are challenging to simulate due to the coupling between the two material phases. Here, we use the reference map technique, a fully Eulerian approach for fluid-solid interaction that is simple to implement and capable of simulating complex multi-body interactions of soft solids. We extend the technique to simulate rigid solids in an incompressible fluid, using a projection step formulated as a composite linear system that simultaneously enforces the rigidity and incompressibility constraints. This projection step is solved efficiently using a Schur complement and a multigrid preconditioner. Several examples including a single body, multiple rigid bodies, and soft-rigid combinations will be presented. |
Monday, November 19, 2018 8:26AM - 8:39AM |
F31.00003: Numerical simulation of mixed convective flow and heat transfer in a staggered double lid driven cavity using Newton-multigrid FEM Shafqat Hussain A computational study has been carried out for the analysis of two dimensional, incompressible and steady mixed convective flow and heat transfer in a staggered double lid driven cavity. The resulting system of equations is discretized using Galerkin finite element method and in particular, the LBB-stable finite element pair Q_{2}/P_{1}^{disc} which lead to 3rd and 2nd order accuracy in the L_{2}-norm for the velocity/temperature and pressure, respectively. The discrete system of nonlinear equations is treated with the help of Newton’s method and the corresponding linear systems are treated using monolithic geometric multigrid solver with Vanka-type smoother. |
Monday, November 19, 2018 8:39AM - 8:52AM |
F31.00004: Determination of Velocity Profile Over and Through Porous Bed Narendra Kumar Patel, Junke Guo, David Admiraal Objectives of this research is to present a unified method to determine the velocity profile over and through the porous bed and to compare this profile with velocity profile over impermeable bed. Equations for flow within bed (Navier-Stokes-Forchheimer) and above the porous bed (Navier-Stokes) are solved, which lead to generate a velocity profile. Theoretically, it is found that for flow within bed, the laminar velocity distribution is expressed by a Jacobi elliptical function. The turbulent velocity distribution also follows a Jacobi elliptical function but compounded with a power of log function. Experimentally, a tracer was injected in the sand bed and its peak concentration was observed at different locations. A fiber optics based sensor was developed to measure the refractive index of water at different locations in the bed to determine the flow velocity. An ADV is used to measure flow velocity above the bed. Ansys Fluent software is used to simulate flow field in porous bed and above the porous bed numerically. We found that our theoretical results well matched with experimental and numerical results which proves the validity of theoretical equations. |
Monday, November 19, 2018 8:52AM - 9:05AM |
F31.00005: Three-dimensional simulations of high-density and high-viscosity laminar and turbulent displacements in canonical and complex geometries Omar K Matar, Lyes Kahouadji, Richard V Craster The displacement of one fluid by another in a pipeline occurs in a wide variety of industrial applications, and has important financial and environmental consequences. The effects of fluid properties, including the density and viscosity ratios, as well as flow regime, whether laminar or turbulent, are studied numerically for horizontal pipe geometries; both miscible and immiscible displacements are considered. The simulations are first validated against analytical solutions available for both the laminar and turbulent regimes. The temporal evolution of the volume fraction of the fluid initially resident in the pipe is tracked as a measure of the effectiveness of the displacement process. The thickness of the film of resident fluid left behind following the initial stages of the flow is also measured and its dependence on system parameters presented. It is also shown that for large viscosity ratios (of order $10^7$), gravitational effects play an important role in the dynamics. Finally, we extend the range of simulations to cover complex geometrical configurations including U-bends, and static mixers, which are of industrial relevance. |
Monday, November 19, 2018 9:05AM - 9:18AM |
F31.00006: Numerical Simulations of Fused Filament Fabrication Gretar Tryggvason, Huanxiong Xia, Jiacai Lu Numerical model and simulations of Fused Filament Fabrication where a filament of hot, viscous polymer is deposited to “print” a three-dimensional object, layer by layer, are presented. A finite volume/front tracking method is used to follow the injection, cooling, solidification and shrinking of the filament. The injection of the hot melt is modeled using a volume source, combined with a moving nozzle, modeled as an immersed boundary. The polymer is taken to be a viscoelastic fluid and an evolution equation for the confirmation tensor is solved along with the conservation equations of momentum and energy. As the polymer solidifies, the stress is found by assuming a hyperelastic constitutive equation. The accuracy and convergence properties of the method are tested by grid refinement studies for a simple setup involving two short filaments, one on top of the other. The effect of the various injection parameters, such as nozzle velocity and injection velocity are briefly examined and the applicability of the approach to simulate the construction of simple multilayer objects is shown. The role of fully resolved simulations for additive manufacturing, their use for validating models of the physics, and as the ``ground truth’’ for reduced order models, is discussed. |
Monday, November 19, 2018 9:18AM - 9:31AM |
F31.00007: Topology optimization using potential flow analysis Jack S. Rossetti, John F. Dannenhoffer, III, Melissa A. Green In current engineering fluid flow systems, space is restricted and traversing 90 degree turns or bends while trying to minimize pressure loss and maintain flow uniformity can be a challenge. Attempts to solve this problem have mainly been through the use of experimental and numerical trial and error methodologies to determine the shape, number, and arrangement of turning vanes, which invokes some experiential knowledge or intuition. Topology optimization presents a general design optimization approach that can produce non-conventional designs. Recently, the fluid dynamics community has adopted topology optimization for low to moderate Reynolds number (Re) flows, but research is lacking for moderate to higher Re, where most of these turning devices operate. As Re increases, the computational expense dramatically increases such that a low-fidelity model is needed to make topology optimization attractive. In this presentation, a topology optimization technique using a low-fidelity potential flow model for initial topology optimization is shown. A method for mapping the potential flow solution to physical boundaries that can be used in a viscous flow solver will be presented, followed by analysis of the topology using a high-fidelity viscous flow solver. |
Monday, November 19, 2018 9:31AM - 9:44AM |
F31.00008: Suppression or Agitation of Vortex-induced Vibration (VIV) of a Cylinder in the Presence of Thermal Buoyancy at Low Reynolds number Hemanshul Garg, Atul Kumar Soti, Rajneesh Bhardwaj We numerically study the effect of thermal buoyancy (acting transverse to the flow) on transverse VIV of an elastically mounted cylinder with the surface, heated to a prescribed temperature. An in-house solver based on sharp interface immersed boundary method is employed (Garg et al., Phys. Fluids., 2018). The numerical simulations are performed for the following parameters: Re = 50, Prandtl number, Pr = 7.1, mass ratio, m = 2, reduced velocity, U_{R} = [4-10], and Richardson number, Ri = [0-4]. At lower Ri, the thermal buoyancy suppresses the vortex shedding and consequently, the maximum amplitude of the cylinder. By contrast, a larger value of Ri shows galloping. Therefore, a critical Ri exists for the transition from the suppression to galloping. For larger (lower) Ri, the variation in the instantaneous pressure force at the cylinder surface over a time cycle is significant enough (constant) to agitate (suppress) the VIV. The vibration frequency remains nearly same for all values of U_{R} for larger Ri, and influence of added mass is observed. These findings could help to design VIV systems in the presence of the thermal buoyancy for energy-harvesting applications. |
Monday, November 19, 2018 9:44AM - 9:57AM |
F31.00009: Reduced order models based on Markovian and Non-Markovian frameworks Abhinav Gairola, Hitesh Bindra, Wentao Guo, Bojan Niceno Empirical mode decomposition for reduced order modeling like POD have been used for efficient dimensionality reduction. However, strong mode truncation may lead to stabilization problems owing to the decoupling of linear and non-linear part of the solutions. Hence, stabilization techniques inspired by turbulence closure model were proposed in the past. Although this process is often effective in stabilization but cannot prevent the information loss which can be essential sometimes for mixing efficiency. A multi-scale approach to model the microscopic dynamics which captures the macroscopic physics of the complex system is presented here. Two novel ideas are pursued 1) to build a simple one dimensional scale preserving reduced order model via the Kramers Moyal expansion 2) to reduce the dimensionality while preserving the smallest scales by projecting the fast decorrelating modes on to the slow modes via the Mori-Zwanzig projection operator. The developed reduced order model i.e. a generalized Langevin equation solves the mode decoupling problem introduced by POD. The model so developed can be used both as a standalone microscopic model of the system and for turbulence closure. Results are presented for a classical test problem and a mixed convective liquid metal channel flow. |
Monday, November 19, 2018 9:57AM - 10:10AM |
F31.00010: An observable regularization of reactive compressible flows Bahman Aboulhasanzadeh, Kamran Mohseni, Matthias Ihme A common feature of many flows involving shocks, turbulence and two-phase flows are the development of a continuous generation of small scales what we identified in the past as $k_\infty$ irregularity. We have recently introduced the concept of observable field quantities, which resulted in the derivation of an observable divergence theorem and eventually the observable Euler and Navier-Stokes equations in order to address the $k_\infty$ irregularity. We have had some promising results in the past simulating flows with shocks, turbulence, and two-phases using observable equations. In this talk we will extend the application of the observable equations to multispecies reactive flow problems. In particular, we present result from simulations of canonical one-dimensional over-driven detonation and deflagration problems. The results of observable simulations will be contrasted against analytical solutions, i.e. ZND solution, and available computations from the literature. All observable simulations are performed using a pseudo-spectral method in order to avoid any contamination of the simulations with numerical dissipation. |
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