Accurate modeling of high-temperature hypersonic flows in the atmosphere requires consideration collision-induced dissociation molecular species and energy transfer between translational internal modes gas molecules. Here, we describe a study N2 + N2⟶N2 2N N2⟶4N nitrogen reactions using quasiclassical trajectory (QCT) method. The simulations used new potential surface for N4 system; is an improved version one that was presented previously. In QCT calculations, initial conditions were...

The direct molecular simulation (DMS) approach is used to predict the internal energy relaxation and dissociation dynamics of high-temperature nitrogen. An ab initio potential surface (PES) calculate two interacting nitrogen molecules by providing forces between four atoms. In near-equilibrium limit, it shown that DMS reproduces results obtained from well-established quasiclassical trajectory (QCT) analysis, verifying validity approach. vibrational time constant for N2–N2 collisions its...

This paper summarizes research performed over the past decade on direct molecular simulation of dilute gas flows. Similar to dynamics method, a potential energy surface is sole model input calculation. However, instead simulating motion all atoms in system deterministically, method uses stochastic techniques and assumptions, adopted from well-established Monte Carlo which are accurate for gases. Using same as input, verified exactly reproduce pure results shock-wave The then used investigate...

Nitrogen dissociation is studied using direct molecular simulation with a new potential-energy surface. Both ${N}_{2}$ - and $N$ processes are simulated as they concurrently take place in an evolving nonequilibrium gas system. The coupling between vibrational excitation quantified leading to several insights.

The direct molecular simulation (DMS) method is used to obtain shear viscosity data for non-reacting air and its components by simulating isothermal, plane Poiseuille subsonic flows. Shear estimated at several temperatures, from 273 K 10 000 K, fitting the DMS velocity profiles using analytic solution of Navier-Stokes equations this simple canonical flow. ab initio potential energy surfaces (PESs) that describe various atomic-level interactions are only input in simulations. Molecules...

We present a microscopic description for the response of crystalline Si nanospheres up to 10 nm in radius various uniaxial compression levels. The behavior at low compressions closely resembles Hertzian predictions. At higher creation new $\ensuremath{\beta}$-tin phase particle core leads (i) volumetric changes (ii) an increase elastic moduli, and (iii) significant hardening. Further, (iv) reversible character transformation is obtained with molecular dynamics simulations. agreement...

This article contains an atomic-level numerical investigation of rovibrational relaxation in molecular nitrogen at high temperature (>4000 K), neglecting dissociation. We conduct our study with the use pure Molecular Dynamics (MD) and Classical Trajectory Calculations (CTC) Direct Simulation Monte Carlo (DSMC), verified to produce statistically identical results conditions interest here. MD CTC DSMC solely rely on specification a potential energy surface: this work, site-site...

This article presents a direct molecular simulation (DMS) of reactive Mach 8.2 oxygen flow over double cone geometry. The free stream conditions and configuration generate with thermal chemical nonequilibrium, which are common attributes hypersonic flight. scenario was first studied experimentally at Calspan University Buffalo Research Center’s test facility. DMS is particle method that uses quantum mechanically derived interaction potentials to simulate collisions within field. Since these...

Sensing atomic and molecular emissions from the radiant plasma sheath that forms around reentry spacecraft will advance understanding modeling of high-enthalpy flows. Optical emission spectroscopy (OES) measurements in this extreme environment can yield data needed to anchor aerothermal flow models Mach [Formula: see text] regime. This paper presents development an OES payload for a commercial capsule, composed commercial-off-the-shelf hardware modified spaceflight. The flight-qualified...

Large-scale molecular dynamics (MD) simulations using the Lennard-Jones potential are performed to study structure of normal shock waves in dilute argon. Nonperiodic boundary conditions flow direction applied by coupling MD domain with a two-dimensional finite-volume computational fluid (CFD) solver correctly generate inflow and outflow particle reservoirs. Detailed comparisons made direct simulation Monte Carlo (DSMC) solutions variable-hard-sphere (VHS) collision model. By performing...

We study the rotational relaxation process in nitrogen using all-atom molecular dynamics (MD) simulations and direct simulation Monte Carlo (DSMC). The intermolecular model used MD is shown to (i) reproduce very well shear viscosity of over a wide range temperatures, (ii) predict near-equilibrium collision number good agreement with published trajectory calculations done on ab initio potential energy surfaces, (iii) produce shock wave profiles excellent accordance experimental measurements....

For the first time in literature, we present 2D simulations of hypersonic flows around a cylinder obtained from accurate ab initio potential energy surfaces (PESs). We compare results low fidelity (empirical) and high (ab initio) PES, thus demonstrating impact PES accuracy on entire aerothermodynamic field body. observe that empirical is not adequate to accurately reproduce rotational vibrational relaxation flow, both compression expansion regions flow field. This approach, enabled by...

We present two-dimensional direct molecular simulation (DMS) results for high-enthalpy nitrogen flows in thermochemical non-equilibrium around a circular cylinder. The simulations are carried out using accurate ab initio potential energy surfaces (PES) to describe N2 + N and interactions. Select comparisons with the Monte Carlo method presented demonstrate how high-fidelity DMS data, both at level of bulk flow quantities local distributions, can be used thoroughly inform or validate...

The molecular dynamics technique with the ab initio based classical reactive force field ReaxFF is used to study adsorption of O2 on Pt(111) for both normal and oblique impacts. Overall, good quantitative agreement experimental data found at low incident energies. Specifically, our simulations reproduce characteristic minimum trapping probability kinetic energies around 0.1 eV. This feature determined by presence a physisorption well in potential energy surface (PES) progressive suppression...

Comparisons are made between potential energy surfaces (PES) for N2 + N and collisions rate coefficients dissociation that were computed using the quasiclassical trajectory method (QCT) on these PESs. For we compare Laganà's empirical LEPS surface with one from NASA Ames Research Center based ab initio quantum chemistry calculations. two PESs (from University of Minnesota). These use different methods computing ground state electronic N4, but give similar results. Thermal coefficients,...

This article presents molecular-level analysis of a reactive, near-continuum, Mach 21 nitrogen flow over blunt wedge using the direct molecular simulation (DMS) method. The conditions lead to internal energy excitation and dissociation in field, resulting thermal chemical nonequilibrium flow. Thermal vibrational mode is observed extend level, where distributions at various points field are be non-Boltzmann. Furthermore, this first reactive DMS calculation wall assumed isothermal full...

The implementation of a nite-rate-catalytic wall boundary condition easily incorporated into generic hypersonic ow solvers is described in detail. Simulations over cylinder are presented using the model parameterized with test air-silica chemical comprising gas-surface reaction mechanisms and their associated rates. It demonstrated that backwards recombination rates should not be arbitrarily set but must consistent gas-phase thermodynamics, otherwise drift from equilibrium state may occur....

A large-scale, fully resolved direct simulation Monte Carlo (DSMC) computation of a non-equilibrium, reactive flow pure oxygen over double cone is presented. Under the simulated near-continuum conditions, computational demands are shown to be significant because wide range length scales that must resolved. Therefore, robust grid adaption capabilities and efficient parallelization Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA) code utilized in this work essential. The...