Measurement and Modeling of Detonation-Driven Shock Tube Flows

Citation

Schoeffler, Donner Thomas (2025) Measurement and Modeling of Detonation-Driven Shock Tube Flows. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/vedz-t661. https://resolver.caltech.edu/CaltechTHESIS:05272025-230901725

Abstract

The detonation driver is a device for generating the strong shock waves used in high-enthalpy hypersonic flow research facilities. The dynamic production of high-pressure and high-temperature driver gas has several advantages for shock-tube performance, however the unsteady gas dynamics of detonation waves also introduces several challenges. These are investigated here analytically and experimentally.

For forward-mode operation, where the detonation propagates into the shock-tube diaphragm, the detonation Taylor wave attenuates the driven shock, and a model is needed to predict the resulting shock dynamics. This is accomplished by first analyzing the problem of plane shock decay generally. A new approximate solution is formulated for the classic piston start-stop problem and shown to be a significant advancement over predecessors. This result is applied to the shock decay from a detonation driver, and a two-parameter model is fit to simulation data, yielding a method for predicting shock trajectories from shock-tube initial conditions.

A small-scale shock tube is designed and constructed using a detonation driver that is operable in both the forward and reverse mode. A transparent driven section is used with large field-of-view shadowgraphy to perform novel time-resolved shock speed measurements. These are used to calibrate the decay model for a forward-mode driver and enable unique observations of shock-speed oscillations, resulting from diaphragm rupture and detonation initiation processes. Results are also obtained for shock tube operation with a conventional high-pressure helium driver.

The gradients and fluctuations in post-shock flows are characterized using a heterodyne focused laser interferometer, a new instrument with advanced capabilities for measuring large phase changes with high resolution. As a development upon the FLDI, spatial filtering characteristics are preserved, and both differential and absolute phase data are acquired simultaneously, enabling a new technique for measurement of gas densities. The instrument is developed, experimentally validated, and then used to probe detonation-driven shock tube flows, achieving phase measurements of over 100 radians with milliradian resolution in a 10 MHz bandwidth. Results from forward-mode operation find that a hydrogen-oxygen driver produces remarkably disturbance-free flows. For reverse-mode operation, the amplitude of flow oscillations is found to be positively correlated with the contact-surface sound-speed ratio, and frequencies are consistent with first-order lateral acoustic waves.

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