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 (P
5 = 11 − 265 atm., T
5 = 780 − 1740 K).

Measurement of reflected-shock bifurcation over a wide range of gas composition and pressure

A viscous boundary-layer model was assembled to help describe the nonideal gas dynamics within shock tubes operating at high densities. The analytical model is based primarily on the landmark work of Mirels, who used the Blasius relation for the turbulent skin friction. The main improvement was the incorporation of a modern friction model for compressible, turbulent boundary layers via changes to the constants and exponents of Mirels's original boundary-layer relations. For example, the wall shear stress now depends on a Reynolds number to the -0.14 power as compared to -0.25 in the original model. As a result, the boundary layer at higher densities is thicker in the present model than in the original one, thus increasing the incident-shock attenuation and related nonuniformities. Even in borderline cases, the boundary-layer transitions to turbulent very quickly, usually within 100 μs for incident-shock pressures greater than about 2 atm. Because a turbulent boundary layer is thicker than a laminar one at the same conditions, the boundary-layer thickness in higher-pressure shock tubes is expected to be a larger fraction of the tube diameter than normally seen in lower-pressure shock tubes

Improved turbulent boundary-layer model for shock tubes

Further Experiments on Shock Tube Wall Boundary-Layer Transition

Discussion de l'article de Chaney et Cook paru ibid. (1983), 21, p 1046. Reponse des auteurs

Comment on 'Further experiments on shock-tube wall boundary-layer transition'

This thesis presents an experimental study of droplet acceleration in a shock-driven two-phase flow. The study serves to identify the characteristics of the boundary layer growth behind a normal moving shock wave in a shock tunnel. Liquid propylene glycol droplets are pre-mixed with air, and slowly injected into the test section of the shock tunnel. Two test sections are evaluated during the course of this study. Each test section is constructed of square, transparent polycarbonate with internal cross section of 7.62 cm. The first test section contains features on the upper and lower surfaces of the test section, consistent with the holes used for the injection system during earlier Richtmyer-Meshkov Instability studies. The second test section has no surface features interfering with the flow, with smooth interfaces. The quiescent air seeded with propylene glycol droplets (diameter 0.5-3μm) is impulsively accelerated with a planar shock wave. A cross-section of the flow is illuminated with multiple pulses from Nd:YAG lasers, producing time-resolved visualizations of the seeded volume. The illuminated images are analyzed to quantify droplet velocity and vorticity from

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Behavior of the Embedded Phase in a Shock-Driven Two-Phase Flow

Shock tube study of boundary layer instability

An experimental study of the spatio–temporal evolution of the transition in a shock-tube wall boundary-layer has been carried out with thin film heat transfer gauges placed all along the tube. The results show that the transition appears, for small initial pressures, under the form of turbulent spots which are periodically created: these spots grow and are transported roughly at a velocity slightly smaller than the inviscid flow, regressing towards the contact surface. For higher initial pressures, a continuous transitional front is created which moves at about the same velocity as the shock-wave. These results seem to explain previous and often contradictory interpretations based on quasi-punctual measurements but the fact remains that the characterization criteria of the transition in unsteady boundary layers are still to be studied.

Pierre Auberger

Papers

Shock tube study of boundary layer instability

Shock tube study of boundary layer instability