**Subgroup 1 – Rarefied Gas Dynamics Modeling Group**

Non-equilibrium rarefied gas dynamics effect has been playing an important role in several scientific and engineering disciplines. These include high-altitude hypersonic flow, reentry flight from orbit with considerable chemical reactions, vacuum technology, micro- and nano-scale gas flows, plume impingement on spacecraft, low-pressure materials processing flow, and comet dust and gas plume, to name a few. These gas flows are either highly rarefied or strongly non-equilibrium, which makes the continuum-based Navier-Stokes equations either breakdown or unsuitable for describing these flow phenomena correctly. Instead, the Boltzmann equation can be used to faithfully describe these flows. Unfortunately, the Boltzmann equation that governs rarefied gas dynamics is generally very difficult to solve numerically. Thus, the particle-based method, the direct simulation Monte Carlo (DSMC) method, developed by Prof. Graem Bird in 1963, has been considered as the most efficient and accurate numerical method for solving the Boltzmann equation statistically. Many advanced DSMC codes were developed in this subgroup, which are summarized as follows:

**PDSC++ (Parallel Direct Simulation Monte Carlo Code using C++)**

- 2D/2D-axisymmetric/3D Unstructured Grid
- Variable Timestep Scheme (VTS)
- Transient Adaptive Subcell (TAS)
- 2D-axisymmetric Simulation w/o Particle Cloning
- Chemical Reaction Module using Total Energy Collision (TEC)
- Chamber Pressure Control Module
- Automatic Convergence Detection Algorithm
- MPI-based Parallel Computing

**Hybrid CUDA-MPI DSMC Code** **(downloaded for more than 600 times within 4 months after its appearance online)**

**Demonstrations**

Axisymmetric DSMC Simulation of Sharp Double-Cone Simulation

Subsonic & Supersonic Test Cases (DREAM – unsteady DSMC)

MONACO vs. PDSC++

*Lo, et. al, “Development, Verification and Applications of a Chemical Reaction Module in PDSC++,” CiCP, 2015.*

RCS Nozzle Plume Modeling

*Wu, et al., Journal of Computational Physics, Vol. 219, No. 2, pp. 579-607, 2006.*

*Lian, et al., Computers & Fluids, Vol. 45, pp. 254–260, 2011.*

3D Hypersonic Sharp Double Cone

3D Apollo Simulation (Pressure & Heating)

****Ref: J.N. Moss et al., “DSMC Simulation of Apollo Capsule Aerodynamics for Hypersonic Rarefied Conditions,” AIAA Paper 2006-3577.*

Other Aerothermodynamics Applications

From: https://www.qarman.eu/

3D QARMAN Simulation (AOA = 0° & 30°)

Large Vacuum Chamber Design

Low-Pressure Material Processing

Pulsed Pressure Chemical Vapor Deposition (collaborated w/ Prof. S. Krumdieck, U. Cantebury, NZ)

Modeling of E-beam Metal Deposition

** Ref: A. **Venkattraman** and A. A. **Alexeenko**, “Direct simulation Monte Carlo modeling of e-beam metal deposition”, Journal of Vacuum Science & Technology A 28, 916 (2010)*

OLED Deposition Simulation (ITRI Project)

Gas Dynamic Model of the Rosetta Comet (w/ Prof. Nick Thomas, University of Bern)

Water Plume on Ceres

*I.-L. Lai “Applications of DSMC Method to the Outgassing of Comets and Dust Jets” Master Theses, NCU, Taoyuan City, Taiwan (2015)*

Curved Jets on 67P Comet

*Z.-Y. Lin, et al., “Observations and analysis of a curved jet in the coma of comet 67P/Churyumov-Gerasimenko” A&A, 588 (2016)*

Photochemical Reaction on 67P Comet

**Lai, et al. “Transport and Distribution of Hydroxyl Radicals and Oxygen Atoms from H2O Photodissociation in the Inner Coma of Comet 67P/Churyumov–Gerasimenko” Earth, Moon, Planets, 117, 23 (2016)*

**Collaborators:**

**Taiwan:****Foreign Countries:**- University of Alabama,Tuscaloosa, USA
- University of Bern, Switzerland
- University of New South Wales, Canberra, Australia
- Institute of Theoretical and Applied Mechanics
- Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia