Thermal radiation from a converging shock implosion

Abstract

High energy concentration in gas is produced experimentally by focusing cylindrical shock waves in a specially constructed shock tube. The energy concentration is manifested by the formation of a hot gas core emitting light at the center of a test chamber at the instant of shock focus. Experimental and numerical investigations show that the shape of the shock wave close to the center of convergence has a large influence on the energy concentration level. Circular shocks are unstable and the resulting light emission varies greatly from run to run. Symmetry and stability of the converging shock are achieved by wing-shaped flow dividers mounted radially in the test chamber, forming the shock into a more stable polygonal shape. Photometric and spectroscopic analysis of the implosion light flash from a polygonal shock wave in argon is performed. A series of 60 ns time-resolved spectra spread over the 8 s light flash shows the emission variation over the flash duration. Blackbody fits of the spectroscopic data give a maximum measured gas temperature of 5800 K in the beginning of the light flash. Line emissions originating in transitions in neutral argon atoms from energy levels of up to 14.7 eV were also detected.

Multi-domain simulations of shock wave interaction with aerodynamic obstacles in cylindrical implosions

“…[4] calculates a value of 0.875 for the eight-sided converging shock. In the twenty four obstacles case, however, due to the very high number of edges, the shape of the reshaped shock remains close to the circular one, described by Guderley, and therefore the original exponent is adopted.…”

“…Differently from Ref. [4], where the complete configuration is simulated, the diverse symmetries of the problem are exploited here in order to reduce the size of the computational domain: a one-dimensional axisymmetrical simulation is performed far from the obstacle region where the implosion can be represented by a shock wave with cylindrical symmetry. Then, two concentric two-dimensional numerical domains are used to represent respectively the reshaping phenomenon, which is the core of the investigation, and the focusing of the shock at the origin.…”

“…The multiple reflections of the shock eventually modify its shape into a more stable one. For symmetrically arranged and suitably shaped obstacles, the final shock shape is prismatic, which corresponds to a more stable configuration [4,5]. On the other hand, the obstacle arrangement is to be optimized to reduce losses due to shock/obstacle interaction [6].…”

Shock dynamics of strong imploding cylindrical and spherical shock waves with real gas effects

“…The present study was initiated in connection with our experimental work on cylindrical shock focusing in argon. 8 In the experimental case the initial pressure was p 1 = 75 mm Hg, which is approximately seven times higher than the initial pressure in Ref. 14.…”

“…The present study is initiated following recent experimental work on converging cylindrical imploding shocks in argon at our shock tube facility at KTH. 8 Whitham's approach of shock dynamics will be adopted, modifying the jump equations accordingly, to account for ionizational and excitational equilibrium behind the shock. For the present conditions, radiation is deemed to play a minor part and is neglected.…”