This paper develops the virtual identity particles (VIP) model to simulate two-phase flows involving complex-shaped particles. VIP assimilates the high efficiency of the Eulerian method and the convenience of the Lagrangian approach in tracking particles. It uses one fixed Eulerian mesh to compute the fluid field and the Lagrangian description to handle constitutive properties of particles. The interaction between the fluid and complex particles is characterized with source terms in the fluid momentum equations, while the same source terms are computed iteratively from the particulate Lagrangian equations. The advantage of VIP is its economy in modeling a two-phase flow problem almost at the cost of solving only the fluid phase with added source terms. This high efficiency in computational cost makes VIP viable for simulating particulate flows with numerous particles. Owing to the spectral convergence and high resolvability of the modal spectral element method, VIP provides acceptable resolution comparable to DNS but at much reduced computational cost. Simulation results indicate that VIP is promising for investigating flows with complex-shaped particles, especially abundant complex particles. 1. Introduction Particles of complex shape, especially in particulate flows, occur widely in scientific research and engineering applications. The most recent advances in the preparation and self-assembly of micron-sized colloids with well-defined anisotropic shapes were reviewed by [1]. Complex and precisely shaped polymeric particles have been made in laboratories to achieve certain functions in advanced materials and microfluids technology [2]. Janus particles have unique anisotropic characteristics, tunable chemistry, and physical properties and have been used in colloidal physics and chemistry for applications including optoelectronics, e-ink, drug delivery, and bioimaging [3]. Complex-shaped metal nanoparticles with controlled morphology and architecture have potential application in material science, chemistry, physics, and medicine [4]. Complex-shaped microgel particles were fabricated via selective polymerization of aqueous two-phase systems [5]. Micro- and nanoparticles of complex shape have been used in various drug delivery applications. The complexity of particle shape does influence biological processes such as circulation, vascular adhesion, and phagocytosis [6]. A systematic study of particles with shape anisotropy and directed assembly of particles into ordered structures via capillary interactions was presented by [7]. Complex particles of any
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