## About

31

Publications

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Introduction

My research interest lies in the area of computational sciences. I am interested in the development of computational models and studying problems related to rarefied gas dynamics: both conventional and rarefied. I am exploring computational methods such as the Direct Simulation Monte Carlo method, Generalized Hydrodynamics, Discontinuous Galerkin method and Molecular Dynamics.

Additional affiliations

Education

July 2012 - July 2018

July 2008 - July 2012

## Publications

Publications (31)

Cross sections for the homo-nuclear atom-diatom collision induced dissociations (CIDs): N2 + N and O2 + O are calculated using Quasi-Classical Trajectory(QCT) method on ab initio Potential Energy Surfaces (PESs). A number of studies for these reactions carried out in the past focused on the CID cross section values generated using London-Eyring-Pol...

A new ab initio based chemical model for a Direct Simulation Monte Carlo (DSMC) study suitable for simulating rarefied flows with a high degree of non-equilibrium is presented. To this end, Collision Induced Dissociation (CID) cross sections for N2+N2→N2+2N are calculated and published using a global complete active space self-consistent field-comp...

A new global potential energy for the singlet spin state O4 system is reported using CASPT2/aug-cc-pVTZ ab initio calculations. The geometries for the six-dimensional surface are constructed using a novel point generation scheme that employs randomly generated configurations based on the beta distribution. The advantage of this scheme is apparent i...

Collision-induced dissociation cross section database for high energy O2–O2 collisions (up to 30 eV) is generated and published using the quasiclassical trajectory method on the singlet, triplet, and quintet spin ground state O4 potential energy surfaces. At equilibrium conditions, these cross sections predict reaction rate coefficients that match...

This study examines the collision dynamics of atom–atom, atom–molecule, and molecule–molecule interactions for O–O, N–N, O2–O, N2–N, O2–N, N2–O, O2–O2, N2–N2, and N2–O2 systems under thermal nonequilibrium conditions. Investigations are conducted from a molecular perspective using accurate O4, N4, and N2O2ab initio potential energy surfaces and by...

The thermal and flow characteristics of nonequilibrium monatomic, diatomic, and polyatomic gases in cylindrical Couette flow are investigated using first-and second-order Boltzmann-Curtiss-based constitutive models. The mixed modal discontinuous Galerkin scheme is used for solving the conservation laws in conjunction with the Maxwell velocity-slip...

Describing diatomic and polyatomic gases at high temperatures requires a deep understanding of the excitation of molecules to a higher vibrational level. We developed new second-order constitutive models for diatomic and polyatomic gases with vibrational degrees of freedom, starting from the modified Boltzmann-Curtiss kinetic equation. The closing-...

This study examines the collision dynamics of atom–atom, atom–molecule, and molecule–molecule interactions for O–O, N–N,O2–O,N2–N,
O2–N, N2–O, O2–O2, N2–N2, and N2–O2 systems under thermal nonequilibrium conditions. Investigations are conducted from a molecular
perspective using accurate O4, N4, and N2O2 ab initio potential energy surfaces and by p...

The present work computationally investigated the combined effects of thermal non-equilibrium and chemical reactions on hypersonic air flows around an orbital reentry vehicle during its reentry. The chemically reacting gas flow around the orbital vehicle was simulated for actual reentry trajectories, with a computational solver based on the Navier–...

Phenomenological models, such as Park’s widely used two temperature model, overpredict the reaction rate coefficients at vibrationally cold conditions and underpredict it at vibrationally hot conditions. To this end, two new chemical reaction models, the nonequilibrium total temperature (NETT) and nonequilibrium piecewise interpolation models for t...

Hypersonic air flow around the Stardust Re-entry Vehicle for diverse ambient conditions is investigated using the Direct Simulation Monte Carlo (DSMC) method. In the present work, the flow field and surface properties on the re-entry vehicle are compared for simulations employing two different chemical reaction models: the traditional phenomenologi...

Shocks encountered in high Mach number flows lead to dissociation of gas molecules. At present, the DSMC codes that simulate such flows under rarefied conditions account for dissociations using phenomenological models such as the total collision energy (TCE) model. However, these models calculate the cross sections using equilibrium rate constants...

Direct Simulation Monte Carlo (DSMC) is a particle method that is widely used to study high Knudsen number flows such as micro-channel flows and hypersonic flow around re-entry vehicles at rarefied ambient atmosphere. The present work fo uses on investigating the flow physics around the re-entry vehicle. Simulating such flows is challenging as the...

Collision Induced Exchange cross-sections for the Zeldovich reaction N2+O⇌NO+N for high energy atom-molecular collisions are calculated using the Quasi-Classical Trajectory method. The dynamical study of O2+N collision is conducted using the 2A′ and 4A′ NO2 PESs reported Sayos et al. Cross-sections for the reverse exchange reaction involving NO + O...

Cross-sections for O2 and N2 dissociation on N2O2 CASSCF-CASPT2 PES are calculated and reported for high energy collisions (up to 30 eV). An earlier reported weighted data fitting scheme for enumerating the entire cross-section database is modified and extended for the N2O2 system. The cross-section database is suitable for studying reactions in hy...

A new chemical reaction model that calculates reactive cross-section using the ab-initio principles has been implemented in Direct Simulation Monte Carlo for studying flows with a high degree of non-equilibrium. In the present work, an alternative to this ab-initio based chemical reaction model that employs fewer parameters for calculating reactive...

Direct simulation Monte Carlo (DSMC) [1] is a particle method that is used to study transition and near-continuum complex flows. In DSMC, every particle represents a large number of real molecules. The DSMC algorithm can be summarized as a sequence of movement and collision phases. Particles are moved in a straight trajectory in the movement phase....

Comparison between the QCT generated CID cross-section and the CID cross-section calculated using the fitting scheme based on spectroscopic weights for 10 random combinations of rovibrational numbers for N 2-N 2 system is shown in Table I. Table II-III lists the coefficient for the fitting function used to interpolate the CID cross-section. The fit...

The use of adaptive grid significantly reduces the overall runtime and gives a more physically realistic collision implementation of the Direct Simulation Monte Carlo(DSMC) method. The present work proposes a new grid scheme, Interpolated Grid(IG), in which the Kumaraswamy distribution is used to fit the density distribution. The grid is constructe...

## Projects

Project (1)

The existing chemical reaction models in available literature (TCE and QK) employed in DSMC method are phenomenological in nature and their use in the study of non-equilibrium flows is questionable. A novel chemical reaction model is formulated that has a stronger theoretical framework. According to the new model, the reactive cross-sections employed in a chemical reaction model are calculated using large ensembles of atomistic simulations. These simulations are carried out using an in-house Quasi-classical Trajectory (QCT) method code. The QCT method requires highly accurate Potential Energy Surface (PES) that need to be based on ab-initio methods. New PESs for O3, O4, N3 and NO2 systems based on highly accurate Multi-Configurational Self-Consistent Field (MCSCF) methods such as Complete Active Space SCF (CASSCF) method and Complete Active Space Perturbation Theory (CASPT2) method are constructed from scratch using MolCAS computational chemistry software. The reaction cross-section database for all important reactions pertaining to Air chemistry are generated and published in the literature. It is found that the DSMC simulations with the new ab-initio based chemical reaction model predicts higher heat flux and heat load on the re-entry vehicle surface compared to the simulations employing TCE and QK phenomenological models. This is a significant inference for engineers designing the Thermal Protection Systems (TPS).
In addition to the present application, the reaction cross-section database is also suitable for developing a non-equilibrium chemical reaction model for Navier Stokes based Computational Fluid Dynamics algorithms. Further, the methodology introduced can be extended to study other systems such as the reactions in Martian atmosphere and reactions in combustion systems.