Measurement of Reflected-shock Bifurcation Over a Wide Range of Gas Composition and Pressure

To determine the extent and magnitude of reflected-shock bifurcation in shock-tube chemistry studies at elevated pressures, experiments were performed using a simple laser schlieren technique and a fast- response pressure transducer. The laser schlieren diagnostic provided a quantitative measurement of the normal-shock passage, an event normally obscured in pressure signals by the bifurcated region. A range of gas mixtures covering molecular weights from 14.7 to 44.0 and specific heat ratios from 1.29 to 1.51 was explored. The results were combined with a standard gas dynamic model to determine the time of arrival of the normal shock wave, the size and strength of the bifurcated region, and the characteristic passage times of dominant features. All results could be expressed in empirical correlations as functions of the gas properties and shock speed. The measured size of the bifurcation zone increased with increasing shock velocity and decreasing specific heat ratio, but displayed no pressure dependence for the conditions of this study (P5 = 11 − 265 atm., T5 = 780 − 1740 K).