Shock tube

Article By:

Bauer, Simon H. Department of Chemistry, Cornell University, Ithaca, New York.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.620500

A laboratory device for rapidly raising confined samples of fluids (primarily gases) to preselected high temperatures and densities. This is accomplished by a shock wave, generated when a partition that separates a low-pressure (driven) section from a high-pressure (driver) section is rapidly removed. In most shock tubes the two sections are separated by a diaphragm that supports the pressure differential until it is punctured (Fig. 1a). Shock tubes operated by rapidly opening valves also have been developed. The tubes can be circular, square, or rectangular in cross section, with diameters that range from 0.8 to 24 in. (2 to 60 cm). The lowest gas pressure to be used in the driven section is such that the corresponding molecular mean free path is several hundred times the diameter of the driven tube; the length of that section should be 40–60 times its diameter. Driven lengths vary, depending on the designed test time and the desired ultimate pressure in the shock tube. Concurrently with propagation of the high-pressure (heating) wave from the partition toward one end wall (Fig. 1b), an expansion (cooling) wave propagates in the opposite direction. Although shock waves can be generated under laboratory conditions by means of a variety of devices, such as ballistic pistons, electrical discharges, distributed explosives, and the impact of hypersonic flows on stationary targets, shock tubes are the simplest to construct and to operate.

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