Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session Z20: Phase Change II |
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Chair: Kishan Bellur, University of Cincinnati Room: 206 |
Tuesday, November 22, 2022 12:50PM - 1:03PM |
Z20.00001: Neutron imaging of evaporation/condensation in cryogenic propellants: an accommodation coefficient study Kishan S Bellur, Ezequiel F Medici, James C Hermanson, Chang Kyoung Choi, Jeffrey S Allen Cryogenic propellent management is critical to long-term space exploration but our understanding of propellant phase change and subsequent boil-off is limited. This is, in part, because the values of accommodation coefficients (inputs to phase change models) are still lacking and experimental data to compute them is limited. A new method to determine accommodation coefficients is developed. Experiments are conducted in the BT-2 Neutron Imaging Facility at the National Institute of Standards and Technology (NIST) by introducing propellant vapor into cylindrical Al6061 and SS316L cells placed inside a 70mm cryostat. Tests are conducted at a range of saturation points between 80 - 230 kPa using H2 and CH4. Phase change is induced through precise control of pressure and/or temperature. Neutron imaging is used to visualize the liquid and evaporation/condensation rates are determined through image processing. Comparing results from a computational model with the experimental data, the accommodation coefficient is explicitly determined. The resulting coefficient values for H2 (0.19 - 0.41) are generally lower than those for CH4 (0.68 - 0.86) and exhibit an inverse relationship with saturation vapor pressure. The results agree well with a generalized transition state theory expression. |
Tuesday, November 22, 2022 1:03PM - 1:16PM |
Z20.00002: New insight into frost growth under turbulent flow conditions using direct numerical simulations Nadim Zgheib, Mahsa Farzaneh, S. A Sherif, S Balachandar We developed a new model to predict frost growth over a flat plate maintained at sub-freezing temperatures and subjected to a relatively hot and moist turbulent air flow. The model consists of a dynamically coupled air-frost system. The air phase is resolved using direct numerical simulations, and the frost phase is modeled from first principles using the conservation equations of mass and energy. The two phases are coupled using either the immersed boundary method or by deforming the bottom boundary and using a body-fitted grid. Due to the vastly different time scales between the fast turbulent flow and the slow frost phase, a slow-time acceleration technique is implemented to make the simulations feasible by accelerating the frost growth. The model is validated against laboratory experiments and then used to predict frost growth under a variety of free-stream and plate conditions. We observe that the Nusselt and Sherwood numbers can be properly scaled so as to become primarily dependent only on the Reynolds, Prandtl, and Schmidt numbers. A series of simulations covering a range of shear Reynolds numbers between 100 and 2000 are then used to extract the Nusselt and Sherwood number dependence on Reynolds number after the frost reaches a finite thickness. |
Tuesday, November 22, 2022 1:16PM - 1:29PM |
Z20.00003: Analysis of Lagrangian dynamics of ammonia spray using computational singular perturbation Lorenzo Angelilli, Pietro Paolo Ciottoli, Francisco E Hernandez Perez, Mauro Valorani, Hong G Im Computational singular perturbation (CSP) is an advanced mathematical tool employed to analyze the different time scales in a physical process. Given a set of five state variables, Lagrangian droplet dynamics is described by a set of five ordinary differential equations (ODEs). Similarly to the existing CSP framework for reacting flows, the modal analysis of the ODE system provides an indication of the active modes and the relative time scales with the definition of a tangential stretching rate (TSR). In addition, by defining all the processes that contributes to the droplet evolution, it is possible to compute time and amplitude participation indices of a single process to the active modes and to the state variables evolution. In this work, the CSP-spray approach is first introduced and applied to single ammonia and acetone droplets to analyze the characteristics of the modes and, subsequently, it is applied to a set of direct numerical simulations of diluted ammonia spray jets, revealing key processes affecting evaporation and clustering of ammonia droplets. |
Tuesday, November 22, 2022 1:29PM - 1:42PM |
Z20.00004: Droplet Solidification: A comparative study of computational models with phase change Lucy J Brown, Suhas S Jain, Parviz Moin Simulations of the dynamic freezing of liquid droplets have applications in both natural and industrial processes. In this work, we perform a comparative study of thermodynamic phase change models coupled with interface-tracking/capturing methods for simulating ice accretion. In particular, we compare the performance and accuracy of existing sharp-interface methods to diffuse-interface methods integrated with phase change models. |
Tuesday, November 22, 2022 1:42PM - 1:55PM |
Z20.00005: The Role of Droplet Modeling in a Five-Field Model of Ice Accretion Arshia Merdasi, Robert Kunz The impingement and ice accretion of droplets on wing surfaces presents a serious challenge to aircraft safety and efficiency. We have developed an Eulerian multiphase model of icing. Five fields are transported including compressible air, water-vapor, droplets, film and ice. An immersed boundary method is employed to accommodate ice accretion. In this talk we will focus on droplet dynamics and heat and mass transfer modeling. Specifically, we have incorporated models for film deposition due to impaction and turbulent diffusion mechanisms, splashing, bouncing and re-entrainment, droplet heat transfer and attendant mass transfer evaporation, condensation, and freezing. We present predictions of collection efficiency on different airfoils to validate the numerous interfacial mass and dynamics models involved in the deposition process. It is found that for airfoil ice-shape modeling at relevant atmospheric conditions, it is critical to incorporate accurate modeling of the impaction, diffusion and splash/bounce elements of deposition processes, whereas re-entrainment is not as dynamically important. Also, the roles of droplet initial conditions (liquid, partially frozen, ice) and size distributions are explored in the context of their impact on ice shape. |
Tuesday, November 22, 2022 1:55PM - 2:08PM |
Z20.00006: Thermodynamic consistency assessment of the multiphase pseudopotential lattice-Boltzmann for liquid spray dynamics Juan G Restrepo-Cano, Francisco E Hernandez Perez, Timan Lei, Kai H Luo, Hong G Im A comprehensive thermodynamic consistency assessment of the pseudopotential lattice-Boltzmann (PP-LB) method, using both the Carnahan-Starling (CS) and the Peng-Robinson (PR) equation of state (EOS) was carried out. For PR EOS, the acentric factor was varied from -0.22 to 0.56. The multi-relaxation times (MRT) collision operator was implemented, while the forcing term was computed using the β-scheme with an 8th-order isotropic Shan & Chen interaction force. The thermodynamic consistency of the PP-LB method was assessed following the behavior of the thermodynamic pressure, the equilibrium densities, and the surface tension. The PP-LB model accurately predicts the equilibrium vapor-liquid densities and satisfactorily captures the theoretical coexistence curve given by the analytical solution of the EOS. The maximum average error for the liquid and vapor branches and density ratio did not exceed 4 % in any of the cases tested for both PR and CS. However, it was found that the predicted thermodynamic pressure deviates from the theoretical, and it is sensitive to the spatial resolution used. The surface tension was retrieved using the Laplace-Young relation. The surface tension was retrieved using the Laplace-Young relation. The predicted surface tension exhibited a consistent behavior with temperature and satisfied the linear relation between the natural logarithm of the surface tension and the liquid-vapor density difference given by the Parachor model. Finally, the applicability of the PP-LB for actual fluids, including alkanes with a different number of carbons, methanol, ammonia, and hydrogen, was evaluated. |
Tuesday, November 22, 2022 2:08PM - 2:21PM |
Z20.00007: A High-Order Numerical Method for Wetting, Dewetting and Heat Transfer Matthias Rieckmann, Florian Kummer The present project was motivated by an experiment in which a heated wall is dragged out of a liquid reservoir with a certain dewetting velocity and wall superheat. For small ratios of dewetting velocity to wall superheat, evaporation occurs mainly in the vicinity of the three-phase contact line. If the dewetting velocity is raised further, the so-called microlayer evaporation (as opposed to contact line evaporation) can be observed experimentally. This is characterized by the formation of an eponymous microlayer of liquid in which evaporation occurs. |
Tuesday, November 22, 2022 2:21PM - 2:34PM |
Z20.00008: Phase separation of a regular binary mixture in the presence of an external force field. Roberto Mauri, antonio bertei, Chih-Che C Chueh The objective of this work is to simulate the phase separation of a regular binary mixture in the presence of an external force field. In general, when a partially miscible binary mixture is brought from the stable, single-phase region of its phase diagram to the unstable region, it separates into two coexisting phases, corresponding to a minimum of the free energy of the mixture. As the mass of each chemical species is conserved, phase transition consists of a reordering process, called spinodal decomposition. |
Tuesday, November 22, 2022 2:34PM - 2:47PM |
Z20.00009: Quasi-Steady Simulations of Glaze Ice Accretion in Turbulent Flow on Aircraft Wings in Supercooled Clouds in the Large Droplet Regime Arash Shad, S. A. Sherif In an attempt to avoid the use of a computationally intensive unsteady simulation while still providing a highly accurate solution, a quasi-steady approach has been adopted to study atmospheric ice accretion in the supercooled large droplet regime in turbulent flow. Quasi-steady solutions can be highly accurate if a sufficiently small time step is selected to advance the solution in time. In this work, we have attempted to find the minimum time interval necessary to adequately simulate the icing process on an aircraft wing in turbulent flow. A mesh morphing scheme has been used which is based on adopting a node displacement in the computations to account for the moving boundaries that are caused by ice buildup. Re-meshing is required in maintaining the grid density of high curvature zones for full quasi-steady simulations. Employing a mesh morphing scheme makes the multi-shot simulations computationally more efficient relative to the full unsteady solution. After successfully modeling glaze icing over an aircraft wing, the effects of supercooled large droplets impacting the wing surface are examined in terms of the behavior of several key variables such as the droplet collection efficiency, water film thickness, and heat transfer rate. In monitoring the droplet collection efficiency and convective heat fluxes at each shot, the approach adopted here was found to be effective in successively reproducing the curvature of the glaze ice horn, which is more discernible for large droplets ($d=50,100,200\hspace{0.2em}\mu m$). Results of the numerical simulations reveal that irregularities in the ice structure, which can be observed either in the horn region or on the bottom surface of the wing, are more influenced by droplet size than by the liquid water content, and become more severe at larger free stream velocities. |
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