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A new multi-species, polyatomic, parallel, three-dimensional Direct Simulation Monte-Carlo (DSMC) solver is developed in this work for applications related to rarefied gas flows. The validation results of our DSMC solver, named as the “Non-equilibrium Flow Solver (NFS)”, are presented in this article. The main features of the NFS solver include its ability to handle multi-species, polyatomic gases for 2D/3D steady and transient nature of flow problems over arbitrary geometries, with a density based grid adaptation technique. Furthermore, 3D surface refinement (for accurate calculation of surface properties) and 3D gas-surface interaction is implemented in a very efficient manner in the solver. The macroscopic flow properties and surface properties, such as heat flux, pressure distribution, drag, can directly be obtained from the solver. The NFS solver is validated for seven test cases related to different two and three dimensional external flow problems of both transient and steady nature. The results obtained using the NFS solver are found to agree very well with both experimental data and those obtained in other numerical works. [ABSTRACT FROM AUTHOR]

Present study concerns the development of a new approach for chemical reaction modelling in DSMC technique. The conventional quantum-kinetic (QK) method based on the VHS collision model is usually applied by the DSMC algorithm to simulate chemical reactions in rarefied gas flowfield. In this paper, a modified quantum-kinetic model (MQK) is presented to remove some limitation of the QK chemical model. The MQK method uses the GSS collision model based on the Stockmayer potential function which can capture both the attractive and repulsive intermolecular forces and polarization effect of the molecules in the reactive flow. To investigate the accuracy and capability of the proposed model, firstly, dissociation of the nitrogen (non-polar gas) and water vapour (polar gas) are simulated in a single cell DSMC for equilibrium and non-equilibrium conditions. The results of the MQK are assessed with those of the QK methods, analytical models and experimental data. Secondly, dissociation of these two types of gases is studies in the rarefied gas flowfield along the stagnation line of a typical hypersonic atmospheric blunt body problem. The flowfield properties including the density, velocity, transient, vibrational and total temperature along the stagnation line and surface properties including the surface pressure and heatflux at the stagnation point obtained by the MQK model are compared with results of the QK method and available analytical and experimental data. The results show that the MQK model provides more accurate results when the polarization effects and both the attractive-repulsive intermolecular forces are dominant especially at high temperature. Also, comparison of the computational cost between two models indicates higher efficiency using the proposed method rather than the QK model due to reduction of number of the collision pairs. [ABSTRACT FROM AUTHOR]

The high-order Runge–Kutta Discontinuous Galerkin (RKDG) method is applied to solve the 2D Boltzmann kinetic equations. A conservative DG type discretization of the non-linear collision relaxation term is formulated for both the Bhatnagar–Gross–Krook and the ellipsoidal statistical kinetic models. Verification is carried out for a steady and an unsteady oscillatory 1D Couette flows, a 2D conduction problem as well as for a 2D long microchannel flow by comparison with the DSMC and analytical solutions. The computational performance of the RKDG method is compared with a widely used second-order finite volume method. The RKDG method has up to 3rd-order spatial accuracy and up to 4th-order time accuracy and is more efficient than the finite volume approach. The parallelization by domain decomposition in physical space is implemented and parallel performance is evaluated. It is shown that 2nd order RKDG is over 15 times faster than the 2nd-order FVM method for the Couette flow test case. The high-order RKDG method is especially attractive for solution of low-speed and unsteady rarefied flows. [ABSTRACT FROM AUTHOR]