Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session A01: Multiphase Flows: Computational Methods I |
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Chair: Taehun Lee, City College of New York Room: Ballroom A |
Sunday, November 19, 2023 8:00AM - 8:13AM |
A01.00001: Conservative two-phase flow simulation using piecewise-parabolic interface reconstructions Fabien Evrard, Robert M Chiodi, Berend van Wachem, Olivier Desjardins To simulate interfacial two-phase flows using finite-volume moment-based methods, e.g., the volume-of-fluid (VOF) or moment-of-fluid (MOF) method, cellwise moment-preserving approximations of the interface are needed in order to conservatively advect the indicator function of the phases. Conservative VOF and MOF methods have so far relied on piecewise-planar interface approximations, necessitating tools for intersecting non-trivial, non-convex polyhedra with a half-space. In this work, we present a new conservative approach that uses piecewise-parabolic interface approximations instead of planar ones. To that end, we first introduce the tools that we have developed for solving the "forward" problem, i.e., calculating the geometrical moments of any non-convex polyhedron intersected by a paraboloid, and the "backward" problem, i.e., reconstructing the paraboloid that optimally and conservatively matches a set of local moments of fluid. We then provide an example of application of these tools in a multiphase flow solver, including the corresponding treatment of surface tension. The resulting framework is validated with canonical and realistic three-dimensional test-cases, from which its accuracy and computational cost are assessed.
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Sunday, November 19, 2023 8:13AM - 8:26AM |
A01.00002: Subgrid-scale modeling of droplet bag breakup Austin Han, Olivier Desjardins We present volume of fluid simulations of an impulsively accelerated liquid drop that undergoes bag regime breakup. While the drop is resolved by as few as ten cells across the initial diameter, the formation of the resulting micron-thickness liquid film is still captured using a dual-plane interface reconstruction. After the liquid film is punctured, a Taylor-Culick retraction model is applied to it in conjunction with a droplet shedding model to predict the time-resolved fragmentation of the film. The resulting droplet size distributions are compared to those from experiments and theoretical work. Finally, the film breakup model is integrated into a simulation of full-scale turbulent air-blast atomization to demonstrate the model's scalability. |
Sunday, November 19, 2023 8:26AM - 8:39AM |
A01.00003: Resolving subgrid scale structures for multiphase flows using the moment-of-fluid method Philippe Hergibo, Timothy N Phillips, Zhihua Xie Multiphase flows are present in many industrial and engineering applications as well as in some physical phenomena. Capturing the interface between the phases for complex flows is challenging and requires an accurate method, especially to resolve fine-scale structures. The moment-of-fluid (MOF) method improves drastically the accuracy of interface reconstruction compared to previous geometrical methods. Instead of refining the mesh to capture increased levels of detail, the MOF method, which uses zeroth and first moments as well as a conglomeration algorithm, enables subgrid structures such as filaments to be captured at a small extra cost. This novel filament MOF method, coupled to a finite volume Navier-Stokes solver, has been tested on a fixed grid and validated using well-known benchmarks such as the Rayleigh-Taylor and the Kelvin-Helmholtz instability problems. Good agreement has been found with benchmark results in the literature and with experimental measurements. |
Sunday, November 19, 2023 8:39AM - 8:52AM |
A01.00004: Conserving mass with the standard level set method to machine precision for two and three-phase flows Kaustubh M Khedkar, Amneet Pal S Bhalla Resolving thin interfaces between various phases is an important consideration in numerical simulations of multiphase flows. In the standard level set method (LSM), the interface between distinct phases is represented by a continuous and differentiable signed distance function. The method is simple to implement, and accurately captures geometrical quantities such as surface normal and curvature, but it leads to spurious mass loss/gain during simulation. Over the past three decades, various fixes and extensions to the standard LSM have been proposed to address mass loss. In practice, some of these methods have not performed well, while others have complicated LSM implementation. A simple mass-preserving technique is presented in this talk for two and three-phase flows that conserves the mass of various phases while maintaining the simplicity of the original technique. Several canonical two-phase liquid-gas and three-phase liquid-gas-solid flow problems are used to demonstrate the new technique's mass-preserving property. |
Sunday, November 19, 2023 8:52AM - 9:05AM |
A01.00005: Numerical and Experimental Analysis of Piezoelectric Inkjet San Kim, Han Seo Ko, Dong Kee Sohn Inkjet technology has diverse industrial applications, such as document printing, display panel manufacturing, additive manufacturing, and so on. With the increasing demand for small droplet jetting, a deeper understanding of the drop formation mechanism is essential. In this study, the jetting dynamics of the piezoelectric inkjet head was analyzed through both numerical and experimental methods. The inkjet head consists of a cylindrical flow channel and a conical nozzle. The droplet ejection and meniscus motion were captured using an inkjet monitoring system with the high-intensity pulsed light. Due to the limited visibility of the experiment, numerical method was used to analyze the flow and pressure inside the inkjet head. An improved model was developed to simulate the overall process of the jetting. The model employed volume of fluid (VOF) method for the multi-phase flow calculation and the dynamic mesh method for driving the piezo actuator. Consequently, the numerical results showed good agreement with the experimental results for both jetting performance and the meniscus motion. |
Sunday, November 19, 2023 9:05AM - 9:18AM |
A01.00006: Three-dimensional Edge-based Interface Tracking (EBIT) Method for Multiphase-flows Simulation with Surface Tension Jieyun Pan, Stephane Zaleski, Stephane Popinet We present a novel Front-Tracking method called Edge-Based Interface Tracking (EBIT) method for multiphase-flows simulation. In the EBIT method, the marker points are located on the grid edges, and the connectivity of markers is implicitly described by a local data structure called Color Vertex, which makes this method suitable for parallelization. Furthermore, the Front-Tracking feature of the EBIT method facilitates its coupling with a boundary model for multiscale computations. In the EBIT method, the marker is advected by a split method. From the position of marker points, we can easily compute the volume fractions. Then the coupling with the Navier-Stokes equations is similar to that in the VOF method. |
Sunday, November 19, 2023 9:18AM - 9:31AM |
A01.00007: A new method for modeling variable surface tension flows using Volume-of-Fluid Mandeep Saini, Vatsal Sanjay, Youssef Saade, Detlef Lohse The flow induced by variable surface tension is encountered in numerous fluid mechanics problems such as Bénard-Marangoni convection, migration of drops/bubbles due to temperature gradients or concentration gradients of surfactants and many more. An accurate numerical modeling of these variable surface tension flows has been a challenging aspect in multiphase flow simulations. A main source of inaccuracies is the arbitrary thickness of the interface imposed by the grid size. Al-Saud and coworkers [1] proposed a sharp interface method based on the continuum surface stress (CSS) model for the level-set method. In this work, we have extended this sharp interface CSS model to a Volume-of-Fluid (VoF) formulation using height functions. Our method is validated with the analytical and numerical solutions of several problems like the motion of bubbles due to varying surface tension, and the two-dimensional thermo-capillary flow between two parallel plates at different temperatures. |
Sunday, November 19, 2023 9:31AM - 9:44AM |
A01.00008: Study of droplet collision regimes using the lattice-Boltzmann method Juan G Restrepo-Cano, Francisco E Hernandez Perez, Hong G Im A multiphase pseudopotential lattice-Boltzmann (PP-LB) based model was implemented to investigate the effect of the impact factor (B) on binary collisions of water droplets. The thermodynamic consistency of the PP-LB model was assessed, showing good agreement with the analytical vapor-liquid equilibrium (VLE) coexistence curve given by the Peng-Robinson equation of state, yielding an average error for the equilibrium densities below 4%. The time evolution of an ellipsoidal oscillating droplet was accurately predicted, with deviations of the oscillation period with respect to the analytical solution below 1%, serving as a benchmark to validate the PP-LB in transient conditions. Lastly, binary droplet collision simulations were conducted using the properties of a water-air system, identifying different regimes (both head-on and off-center coalescence, reflexive separation, and stretching separation) and investigating their characteristic features such as liquid filament formation, droplet rotation, satellite droplet formation. The effect of the impact factor was examined, finding that as B increases, the formation of satellite droplets is favored. In addition, a droplet rotation was observed, due to the inertia and vertical distance between the centers of the droplets. |
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