Shmuel Eidelman

Pulsed Detonation Engine: Key Issues

We examine key issues that determine pulsed detonation engine (PDE) propulsive efficiency. Using Computational Fluid Dynamics methodology (CFD), we conducted performance analysis for the device for which we demonstrated multi-cycle operation experimentally. The analysis is focused on the effects of the non-ideal detonations on the propulsive efficiency. General questions of the methodology of nonsteady engine cycle analysis and performance evaluation are examined.

A second-order Godunov scheme on a spatial adapted triangular grid

Abstract Spatial adaptation procedures for the accurate and efficient solution of unsteady inviscid flow simulation are described. The adaptation procedures were developed and implemented applying a second-order Godunov scheme. These procedures involve mesh enrichment/coarsening to either add/remove vertices in high/low gradient regions of the flow, respectively. The goal is to achieve solutions of high spatial accuracy at minimal computational cost. The paper describes a very effective error estimator to detect high/low activity regions of the flow to be enriched or coarsened, respectively. The error estimator is based on total energy and density fluxes into the cell combined with gradient of density. Included in the paper is a detailed description of the direct dynamic refinement method that is used for adaptation. A detailed simulation of a reflection and diffraction of multiple shock waves flowing over a diamond shape wedge is presented and compared with experimental results. The simulated results are shown to be in excellent agreement with the experiment primarily in that all the complicated features of the physics are accurately accounted for and the shock waves, slip lines, vortices are sharply captured.

Synthesis of nanoscale materials using detonation of solid explosives

Abstract Direct synthesis of nanophase materials in detonations is considered. This article describes a number of methods that can lead to the formation of super saturated states of media, which in turn will precipitate as nanoscale particles when the detonation products are quenched in the expansion process. Several examples are given of reactions that will lead to production of nanophase particles of metals, oxides, diamond and other unique materials. It is shown that conditions of nucleation and growth of nanoscale material can be analyzed using advanced methods of computer simulation of detonation and blast wave phenomena. An example of this kind of simulation is given. It is concluded that detonative synthesis of nanophase material can lead to low cost technology that will produce a range of unique materials.

Numerical Simulation of Shock Wave Reflection and Diffraction in a Dusty Gas

The unsteady shock wave reflection and diffraction generated by a shock wave propagating over a semicircular cylinder in a dusty gas are studied numerically. The mathematical model is a multi-phase system based on a multi-fluid Eulerian approach. A Second Order Godunov scheme is used to solve the gas phase Euler equations and an upwind scheme is used to solve the particle phase conservation equations on an unstructured adaptive mesh. For the validation of the model, the numerically predicted one-dimensional shock wave attenuation is compared with experimental results. Shock wave reflection and diffraction over a semicircular cylinder in a pure gas flow is simulated first to show the excellent agreement between the present computation and the experimental results. For the shock wave reflection and diffraction in a dusty gas, the effects of particle size and particle loading on the flow field are investigated. Gas and particle density contour plots are presented. It has been shown that the shock wave configuration differs remarkably from pure gas flow depending on the particle parameters. The difference is explained as the result of momentum and heat exchange between the two phases.

Detonation Wave Propagation in Combustible Particle/Air Mixture with Variable Particle Density Distributions

Abstract Abstract—A mathematical model is presented describing a physical system of detonation waves propagating in a solid particle/air mixture with a wide range of solid phase concentrations. The mathematical model was solved numerically using the Second Order Godunov method, and numerical solutions were validated for detonation waves propagating in mixtures with concentrations of solid phase from 0.75 kg/m3 to 1000 kg/m. Numerical solution was obtained for detonation waves propagating in a system consisting of clouds with a small concentration of particles and a ground layer in which solid particle densities are three orders of magnitude larger than in the cloud. Three different particle concentration distributions in the ground layer were simulated and compared in terms of detonation wave structure and parameters.

Nonlinear signal processing using integration of fluid dynamics equations

Here, we describe a new and unique image sharpening method based on computational techniques developed for CFD. Our preliminary experience with this method shows its capability for nonlinear enhancement of image edges as well as deconvolution of an image with random noise. This indicates a potential application for image deconvolution from sparse and noisy data resulting from measurements of backscattered laser-speckle intensity.

Solution of Euler's equations on adaptive grids using a fast unstructured grid second order Godunov solver (FUGGS)

We describe a new technique for solving Eulers gasdynamic equations on unstructured triangular grids with arbitrary connectivity. The formulation is based on the second order Godunov method. The use of data structure with only one level of indirectness leads to an easily vectorized and parallelized code with a low level of overhead in memory requirement and high computational efficiency. The performance and accuracy of the algorithm has been tested for a very wide range of Mach numbers starting from very low subsonic to high hypersonic flows, without the need to adjust any code parameters. The algorithm was implemented in a vertex based and triangle based scheme. The computational results produced by the triangle based version showed an extremely low level of artificial viscosity.

Numerical and analytical study of transverse supersonic flow over a flat cone

Quasisteady supersonic flow over a flat cone on a plane surface is studied. A formula is derived for the angle through which the flow lines turn at the cone. The results are used to justify the use of two-dimensional simulations of the flow. Peak pressures and total impulses are obtained numerically for various cone angles.