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Ramat HaSharon, Israel

Peles O.,IMI RSD | Yaniv S.,IMI RSD
55th Israel Annual Conference on Aerospace Sciences 2015 | Year: 2015

This paper presents Large Eddy Simulation (LES) capability added to IMI/RSD CFD code FLDYNS. There are major differences between RANS and LES solvers. RANS equations are usually solved using second or third order upwind schemes. It turns out that low order upwind schemes with their inherent dissipation are not suitable for LES. Schemes suitable for LES must have very low dissipation, hence, one should use high order central schemes or in some cases high order upwind schemes. A high order central scheme is represented and examined in this paper. In order to check the quality of this scheme, time dependent problem and vortex convection problem are solved and their accuracy is tested. Source


Sivan J.,Hebrew University of Jerusalem | Haas Y.,Hebrew University of Jerusalem | Grinstein D.,IMI RSD | Kochav S.,IMI RSD | And 2 more authors.
Combustion and Flame | Year: 2014

The effect of boron particle size on the combustion characteristics of B/KNO3 pyrotechnic mixtures is examined experimentally. Following ignition by a high power diode laser, the pressure and light emission were recorded as a function of time. Ignition delay times and combustion spectra were found to vary significantly upon changing the boron particle size. Samples containing sub-micron boron particles (~mean diameter of 1μm) ignite much faster than micron-sized ones (30-150μm mean diameter). The sub-micron samples are also characterized by high intensity light emission during combustion, due primarily to BO2 emission whereas in the larger boron samples black-body radiation dominates the spectra. The data were analyzed and compared with predictions of standard thermal ignition theory. It was found that a semi-inert solid model in which the laser is the sole heat source does not reproduce the experimental results. Instead a model of a single spherical boron particle embedded in a mixture of boron and potassium nitrate and heated by a laser source is introduced. In this model boron particles act as hot spots absorbing the laser energy and dissipating it in the matrix. Ignition is assumed to occur when the B/KNO3 matrix surrounding the hot particle reaches the decomposition temperature of potassium nitrate. A reasonable correlation between experimental and predicted ignition delay times is obtained for all intensities and boron particle sizes studied. © 2014 The Combustion Institute. Source

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