Influence of shear layers on the structure of shocks formed by rectangular and parabolic blockages placed in a subsonic flow-field

Cheeda, Vijaya Kumar; Kumar, Amit; Ramamurthi, K.

doi:10.1007/s00193-013-0476-1

Cited by 9 publications

(2 citation statements)

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“…The expansion of product gas causes high-speed flow and this flow can form strong shock waves. Such strong shock waves can generate a vortex of about one-fourth of the confinement size [28,29] due to RTI and RMI [30]. Therefore the flame spins across the duct until the fuel is consumed in the enclosure.…”

Section: Resultsmentioning

confidence: 99%

Turbulent flame propagation in corn dust clouds formed in confined and open spaces

Cheeda

2020

SN Appl. Sci.

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Flame propagation stages in a corn dust cloud in a large room size confinement investigated. The clouds ignited by a weak heat source. The mass of the dust identified to be influenced the flame acceleration. Dust in the clouds burnt rapidly through several fluid dynamic mechanisms. Four types of instabilities contributed to fast flame development. Landau-Darrieus and Kelvin-Helmholtz instabilities increased the flame speed in the initial stages of the fireball. In the intermediate and final stages, corrugated and the wrinkled flame structure originated through Rayleigh-Taylor instabilities. In addition to flow aspects and instabilities, the shock waves also enhanced the flame speed. The shock overpressure measured with a dynamic pressure sensor. These shock waves induced Richtmyer-Meshkov instability in the fireball and developed turbulent flames. Density gradients across the fireball (due to higher temperature gradients) caused perturbations. Further, this gradient increased by the shock waves. The crosswind speed through the confinement windows was slower, therefore it has not enhanced the flame speed. Corn dust dispersed quickly to a wider area by the shock waves, established large dust clouds, and lead to explosions. The maximum surface temperature of the fireball predicted as 1384 K. The preheat zone around the fireball identified by an image processing tool. The turbulence parameters at the fireball obtained from qualitative and quantitative methods and analyzed. The clouds of a small quantity of corn dust lead to the formation of larger fireballs due to higher kinematic viscosity than the energy dissipation rate. Keywords Dust cloud explosion • Hydrodynamic instability in dust cloud explosions • Turbulent flame • Fire accidents and Fire safety List of symbols LDI (DLI) Landau-Darrieus instability also referred to as Darrieus-Landau instability KHI Kelvin-Helmholtz instability RTI Rayleigh-Taylor instability RMI Richtmyer-Meshkov instability DAQ Data acquisition system FPS Frames per second R e Reynolds number D a Damköhler number K a Karlovitz number p D Dynamic pressure Fluid density u ′ Turbulent intensity, velocity component L T Integral turbulent length scale L

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Section: Resultsmentioning

confidence: 99%

Turbulent flame propagation in corn dust clouds formed in confined and open spaces

Cheeda

2020

SN Appl. Sci.

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“…The run up distance viz., the distance between the ignition source and the point at which the detonation is formed has also been evaluated. The blockage ratio, which represents the area of the blockages normal to the flow to the total cross sectional area, has been identified as a parameter governing the run-up distance [14,3]. Since the expansion waves, originating at the blockages, get reflected at the top wall or ceiling and these reflected waves interact with the shear layer to form compression waves, the characteristic height of the confinement would essentially influence the formation of the wave structure and hence the turbulence downstream of the blockages.…”

Section: Introductionmentioning

confidence: 99%