Advances in Direct Simulation Monte Carlo: From Micro-scale to Rarefied Flow Phenomena

This book provides a comprehensive and in-depth presentation of recent advancements in the Direct Simulation Monte Carlo (DSMC) method, focusing on modern collision algorithms that maintain accuracy even with low particle-per-cell. Drawing from theoretical insights and computational innovations, it bridges fundamental kinetic theory with practical simulation techniques for rarefied gas flows.

Structured across ten chapters, the book begins with a discussion of micro- and nanoscale fluid flows, where non-equilibrium effects and rarefaction become dominant. It explores key phenomena in MEMS/NEMS devices, such as velocity slip, temperature jump, Knudsen minimum, and thermal polarization—essential for understanding transport in confined geometries.

A strong emphasis is placed on advanced DSMC collision schemes, including the BT-family of algorithms (e.g., SBT, ISBT, GBT, SSBT, and SGBT), as well as emerging hybrid approaches such as DSMC-Fokker-Planck and Low-Variance DSMC. Applications span from pressure-driven microchannel flows, thermally induced rarefied flows, and Couette/cavity configurations, to supersonic wedge flows and nonlinear instability phenomena like Rayleigh–Bénard convection in rarefied gases.

Special attention is given to semi-analytical aerodynamic models in free-molecular regimes, making the book particularly valuable for those working in aerospace applications at high altitudes or in low-density environments.

With contributions from leading experts, this expanded volume serves as both a reference and a teaching guide for researchers and students in rarefied gas dynamics, microfluidics, and high-fidelity particle-based simulation methods.

Ehsan Roohi is currently a visiting associate professor at Embry Riddle Aeronautical University, Daytona Beach. In September 2025, he will join the Mechanical and Industrial Engineering Department at the University of Massachusetts Amherst. He received his Ph.D. degree from the Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran, in 2010, with a sabbatical visit at the University of Strathclyde, Uk. He was a University Professor at the Ferdowsi University of Mashhad, Iran and Xi’an Jiaotong University, China. He worked at the University of Maryland, School of Medicine, and the Department of Mechanical Engineering at Johns Hopkins in 2023-2024. He is an expert in direct simulation Monte Carlo (DSMC) techniques and has published several papers on new collision models in DSMC. His research primarily involves utilizing numerical models to explore rarefied gas dynamics in outer space and at micro and nano scales. He developed new propulsion systems for spacecraft, benefiting from solar radiation. He published more than 130 journal papers in prestigious journals such as Journal of Fluid Mechanics, Journal of Computational Physics, and Physics of Fluids. 

Dr. Hassan Akhlaghi received his B.Sc., M.Sc., and Ph.D. in Aerospace Engineering from Sharif University of Technology, Tehran, Iran, in 2007, 2010, and 2020, respectively. Since Sep. 2024, Dr. Akhlaghi has been an assistant professor in the Faculty of New Science and Technology, University of Tehran. Dr. Akhlaghi focuses on the research of rarefied gas dynamics and micro-/nano-scale gas flows. His research interests include rarefied gas flows simulation using the DSMC method, algorithm development in the DSMC method, gas flow investigation in microchannels, flow physics of rarefied gas flows, etc. Since 2008, Dr. Akhlaghi has published 42 peer-reviewed technical papers in international journals and conferences. He served as a reviewer for several international journals. He was awarded the top Researcher Award, which recognized his achievement as one of the most highlighted research outputs performed by Sharif University of Technology in 2019–2020. 

Dr. Stefan Stefanov is a professor at the Institute of Mechanics, Bulgarian Academy of Sciences, Sofia, Bulgaria. He received a Doctor of Science in Applied Mathematics from Sofia University in 1987. Prof. Stefanov is interested in topics including microfluidics, kinetic theory of gases, fluid mechanics, flow instabilities, self-organized fluid systems, transition to turbulence, partial differential equations, numerical methods in fluid mechanics, and Monte Carlo numerical methods (with particular interest in the Direct Simulation Monte Carlo (DSMC) method).