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...

A variant of the direct simulation Monte Carlo (DSMC) method, referred to as molecular (DMS), is used study oxygen dissociation from first principles. The sole model input DMS calculations consists 12 potential energy surfaces that govern O2 + and O collisions, including all spin-spatial degenerate configurations, in ground electronic state. are representative gas evolution behind a strong shock wave, where excites rotationally vibrationally before ultimately dissociating reaching...

This work presents the analysis of non-equilibrium energy transfer and dissociation nitrogen molecules (N2(Σg+1)) using two different approaches: direct molecular simulation (DMS) method coarse-grain quasi-classical trajectory (CG-QCT) method. The methods are used to study thermochemical relaxation in a zero-dimensional isochoric isothermal reactor which heated several thousand degrees Kelvin, forcing system into strong non-equilibrium. considers for temperatures ranging from 10 000 25 K....

This paper presents molecular dynamics calculations of vibrational energy transfer and nonequilibrium dissociation in collisions. The interactions are modeled using nine potential surfaces corresponding to the , states, which govern electronically adiabatic collisions ground-electronic-state diatomic oxygen with atomic oxygen. Characteristic excitation times calculated over a temperature range rate coefficients . Vibrational relaxation rates, specific each PES, found vary by an order...

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...

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...

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...

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...

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...

In this work we present a molecular level study of N2+N collisions, focusing on excitation internal energy modes and non-equilibrium dissociation. The computation technique used here is the direct simulation (DMS) method interactions have been modeled using an ab−initio potential surface (PES) developed at NASA's Ames Research Center. We carried out vibrational calculations between 5000K 30000K found that characteristic time for N + N2 process was order magnitude lower than predicted by...

We present a Mach 15 air flow over blunt two-dimensional wedge simulated using the direct molecular simulation method. As electronically excited states are not modelled, resulting mixture around contains electronic ground only, namely ${\rm N}_2(\text {X}^1 \varSigma _g^{+})$ , O}_2(\text {X}^3 _g^{-})$ NO}(\text {X}^2\varPi _r)$ N}(^4{\rm S})$ and O}(^3{\rm P})$ . All potential energy surfaces (PESs) that used to model various interactions between particles ab initio with two notable...

The accurate characterization of molecular transport properties is essential for high-fidelity simulations reactive, hypersonic flows. correct prediction energy and mass diffusion in the laminar, high-temperature, multicomponent boundary layer a hyper-velocity flow has profound implications modeling gas-surface interactions thermal loads on aeroshell. In this work, investigated by solely using $a\phantom{\rule{0}{0ex}}b$...

Kinetic rates for thermochemical nonequilibrium models are generally computed from quasiclassical trajectory (QCT) calculations on accurate ab initio potential energy surfaces (PES). In this article, we use a feed-forward artificial neural network (ANN) to fit existing single-point energies ${\mathrm{N}}_{2}+{\mathrm{N}}_{2}$ interactions [Bender et al., J. Chem. Phys. 143, 054304 (2015)] construct PES suitable molecular simulation of high-temperature gas flows. We then perform detailed...

In this article we provide a comparative study of rate laws for internal energy excitation and dissociation nitrogen. These thermochemical properties are obtained by studying molecular interactions on two independently developed $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ potential surfaces at the University Minnesota NASA Ames Research Center. Furthermore, comparison canonical...