Numerical Modelling of Caseless Ammunition with Coreless Bullet in Internal Ballistics

In the search of a new weapon for combat in short range, it is proposed the use of a new experimentally designed 7.62 mm calibre ammunition with a lighter weight (caseless-coreless). This can be used in carbine assault rifles with short barrel or pistols. In this work, the compressible gases flowing through the gun barrel caused by the proposed ammunition were experimentally and numerically analysed. The Large Eddy Simulation was used for the numerical simulation, considering a compressible and turbulent flow, with the chemical species transport model and a complete conversion of the propellant reaction. Variations in pressure and temperature were compared with the results obtained from a conventional 7.62 mm full metal jacket (FMJ) ammunition. Results of ballistic experimental tests and numerical simulations were similar than those of the 9 mm x 19 mm FMJ ammunitions, showing feasibility for the development of new weapons intended for operations of short range shots.Defence Science Journal, Vol. 65, No. 3, May 2015, pp.203-207, DOI: http://dx.doi.org/10.14429/dsj.65.851

The Pencil Code, a Modular MPI Code for Partial Differential Equations and Particles: Multipurpose and Multiuser-maintained

The Pencil Code is a highly modular physics-oriented simulation code that can be adapted to a wide range of applications. It is primarily designed to solve partial differential equations (PDEs) of compressible hydrodynamics and has lots of add-ons ranging from astrophysical magnetohydrodynamics (MHD) (A. Brandenburg & Dobler, 2010) to meteorological cloud microphysics (Li et al., 2017) and engineering applications in combustion (Babkovskaia et al., 2011). Nevertheless, the framework is general and can also be applied to situations not related to hydrodynamics or even PDEs, for example when just the message passing interface or input/output strategies of the code are to be used. The code can also evolve Lagrangian (inertial and noninertial) particles, their coagulation and condensation, as well as their interaction with the fluid. A related module has also been adapted to perform ray tracing and to solve the eikonal equation. The code is being used for Cartesian, cylindrical, and spherical geometries, but further extensions are possible. One can choose between different time stepping schemes and different spatial derivative operators. High-order first and second derivatives are used to deal with weakly compressible turbulent flows. There are also different diffusion operators to allow for both direct numerical simulations (DNS) and various types of large-eddy simulations (LES)

Effects of pressure and Karlovitz number on the turbulence-flame interactions in lean premixed H2/air flames

This paper presents three-dimensional direct numerical simulations of lean premixed turbulent H2/air flames in the thin and distributed reaction zones, with the Karlovitz numbers at 60, 110, 150 and 1000, and pressures at 1 and 5 atm, respectively. Flame front structures and chemical pathways are examined in detail to investigate the effects of pressure and turbulence on flames. There is an increasing number of finer structures on the flame front with increased Karlovitz number. Eddy structures are observed downstream of the reaction zone under high turbulence intensity and thus Karlovitz number, indicating that the turbulent eddies are small and energetic enough to break through the distributed reaction zone. Statistical analysis indicates that the probability of high curvatures increases with increasing Karlovitz number at a constant pressure. When the Karlovitz number is kept constant, the probability of high curvatures is significantly higher at the atmospheric pressure than at elevated pressure. The approximation of Schmidt number (Sc = 1) in theoretical analysis introduces errors in the estimation of the smallest flow scale and the Karlovitz number. Accordingly, in the turbulent flame regime diagram, the boundary between the thin reaction zone and the distributed reaction zone should be modified at the elevated pressure. Moreover, the decorrelation of heat release and H2consumption is directly related to turbulence intensity, and the decorrelation is reduced at the elevated pressure. Due to the enhanced radical transport at high Karlovitz number, chemical pathways can be locally changed, which is more significant at elevated pressure

An extended flamelet-based presumed probability density function for predicting mean concentrations of various species in premixed turbulent flames

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean, complex-chemistry, hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach for evaluating mean species concentrations. For this purpose, dependencies of mole fractions and rates of production of various species on a combustion progress variable c, obtained from the laminar flame, are averaged adopting either the actual Probability Density Function (PDF) P(c) extracted from the DNS data or a common presumed β-function PDF. On the one hand, the results quantitatively validate the flamelet approach for the mean mole fractions of all species, including radicals, but only if the actual PDF P(c) is adopted. The use of the β-function PDF yields substantially worse results for the radicals’ concentrations. These findings put modeling the PDF P(c) on the forefront of the research agenda. On the other hand, the mean rate of product creation and turbulent burning velocity are poorly predicted even adopting the actual PDF. These results imply that, in order to evaluate the mean species concentrations, the flamelet approach could be coupled with another model that predicts the mean rate and turbulent burning velocity better. Accordingly, the flamelet approach could be implemented as post-processing of numerical data yielded by that model. Based on the aforementioned findings and implications, a new approach to building a presumed PDF is developed. The key features of the approach consist in (i) adopting a re-normalized flamelet PDF for intermediate values of c and (ii) directly using the mean rate of product creation to calibrate the presumed PDF. Capabilities of the newly developed PDF for predicting mean species concentrations are quantitively validated for all species, including radicals

Detailed Numerical Simulations of Turbulent Premixed Flames at Moderate and High Karlovitz Numbers

In generally accepted and applied flamelet combustion models, a turbulent flame is mainly assumed distorted by the large-scale turbulence eddies, whereas small-scale turbulence effects on the local flamelet structures are neglected. However, in a lot of industrial applications rather high turbulent intensities are often imposed, which induce turbulence scales at ranges smaller than the flame thickness. Flame/turbulence interaction appears quite different at these small scales, which is why improvement of the combustion models is required to account for these phenomena. In this thesis, direct numerical simulations (DNS) and large eddy simulations (LES) have been utilized for studies of lean premixed turbulent reactive flows at various turbulent intensities. DNS has been applied for detailed studies of flame-turbulence interaction to investigate flame structures and detailed chemistry effects at high Karlovitz numbers. Intensified convective-diffusive transport within the fine reaction zone layers is observed which is found to significantly alter the chemical pathway with, e.g., intensified heat release rate at low temperatures. Based on these observations a categorization, supplementary to the conventional one, is proposed, which is able to incorporate detailed chemistry effects into the classification of turbulent premixed flames at high Karlovitz numbers. The effect of differential diffusion was found significant, both globally (in terms of the fuel diffusion effect) and locally (in terms of the radical diffusion effect), also in the distributed reaction zone regime. LES was employed for a low swirl stabilized flame utilizing a flamelet combustion model approach. A dynamic modeling approach to incorporate sensitivity to local variations in the subgrid scale flame wrinkling was implemented and validated. The simulations showed high sensitivity of the prediction of turbulent flame fluctuations as well as ambient air entrainment rate into burned gases to inflow conditions and operating conditions. Lower sensitivity was found to domain size and combustion model. Overall the model results showed good agreement with the velocity and scalar validation data in the thin reaction zone regime. In order to analyze the influence of frequency specific coherent structures on the flame dynamics extended dynamic mode decomposition was performed which was able to delineate the effects of the inner and outer shear layer vorticity on the flame stabilization