In this paper, a three-dimensional (3D) cascaded lattice Boltzmann method (CLBM) is implemented to simulate the liquid-vapor phasechange process. The multiphase flow field is solved by incorporating the pseudopotential multiphase model into an improved CLBM, the temperature field is solved by the finite difference method, and the two fields are coupled via a non-ideal equation of state. Through numerical simulations of several canonical problems, it is verified that the proposed phase-change CLBM is applicable for both the isothermal multiphase flow and the liquid-vapor phase-change process. Using the developed method, a complete 3D pool boiling process with up to hundreds of spontaneously generated bubbles is simulated, faithfully reproducing the nucleate boiling, transition boiling, and film boiling regimes. It is shown that the critical heat flux predicted by the 3D simulations agrees better with the established theories and correlation equations than that obtained by two-dimensional simulations. Furthermore, it is found that with the increase in the wall superheats, the bubble footprint area distribution changes from an exponential distribution to a power-law distribution, in agreement with experimental observations. In addition, insights into the instantaneous and time-averaged characteristics of the first two largest bubble footprints are obtained.
Characterizing the key length and energy scales of intermolecular interactions, Lennard-Jones parameters, i.e., collision diameter and well depth, are prerequisites for predicting transport properties and rate constants of chemical species...
Summary In this paper, a novel immersed boundary method is developed, validated, and applied. Through devising a second‐order three‐step flow reconstruction scheme, the proposed method is able to enforce the Dirichlet, Neumann, Robin, and Cauchy boundary conditions in a straightforward and consistent manner. Equipped with a fluid‐solid coupling framework that integrates high‐order temporal and spatial discretization schemes, numerical experiments concerning flow involving stationary and moving objects, convex and concave geometries, no‐slip and slip wall boundary conditions, as well as subsonic and supersonic motions are conducted to validate the method. Using analytical solutions, experimental observations, published numerical results, and Galilean transformations, it is demonstrated that the proposed method can provide efficient, accurate, and robust boundary treatment for solving flow with arbitrarily irregular and moving geometries on Cartesian grids. On the basis of the proposed method, the development of a solver that unifies one‐, two‐, and three‐dimensional computations and the generation of complex geometric objects via simply positioning components are described. In addition, a surface‐normalized absolute flux is proposed for interface sharpness measurement, and an analytically solvable modified vortex preservation problem is developed for a convergence study concerning smooth flow with irregular geometries.
Explosively dispersed granular materials frequently exhibit coherent particle clustering and jetting structures. Influencing the mass concentration and related particle reaction and energy release, this phenomenon is of significant interest to the study of flow instability and mixing in heterogeneous detonation and explosion. Largely inhibited by the complex mesoscale multiphase interactions involved in the dispersal process, the underlying mechanism remains unclear. In this study, mesoscale direct simulations that capture coupled multiphase interactions and deterministic granular dynamics are conducted to investigate particle clustering and jetting formation in explosively dispersed granular payloads consisting of inert particles. Employing a mesoscale simulation framework that models particles as discrete entities and resolves the interfaces and collisions of individual particles in stochastically generated payloads with randomly distributed particle positions and sizes, numerical cases that cover a set of stochastic payloads, burster states, and coefficients of restitution are solved and analyzed. A valid statistical dissipative property of the mesoscale discrete modeling with respect to Gurney velocity is demonstrated. The predicted surface expansion velocities can extend the time range of the velocity scaling law with regard to Gurney energy in the Gurney theory from the steady-state termination phase to the unsteady evolution phase. Dissipation analysis based on the mesoscale discrete modeling of granular payloads suggests that incorporating the effects of porosity can enhance the prediction of Gurney velocity for explosively dispersed granular payloads. On the basis of direct simulations, an explanation for particle clustering and jetting formation is proposed to increase the understanding of established experimental observations in the literature.
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