Blast wave induced unsteady flow at the shock tube opening

TL;DR

This study investigates the complex unsteady flow phenomena generated by blast waves in an open-ended shock tube, revealing new transient features and providing an approximate model for blast evolution and flow interactions.

Contribution

The paper introduces detailed experimental observations and an approximate model of blast wave dynamics at the shock tube opening, including previously unreported unsteady features.

Findings

Identification of reverse shock formation and embedded shock shedding.

Development of an approximate power-law density profile model.

Validation of steady-pressure outlet conditions for accurate flow prediction.

Abstract

Shock tubes have been a crucial device, facilitating studies across a wide range of practical applications. An open-ended shock tube employing the wire-explosion technique with a rectangular cross section is used in the present study to generate blast waves over a Mach number range of 1.2-1.8, enabling detailed investigation of unsteady compressible flow at the tube opening. The blast wave produces a complex flow field comprising a compressible vortex ring with a trailing jet, and several transient structures, including embedded shocks, inward-moving shock or reverse shocks, shear layers, and Prandtl-Meyer expansion fans. An approximate model based on a power-law density profile describes the blast evolution inside and outside the tube, with the equivalent source deduced from measured shock trajectories. The blast wave-tube exit interaction is analyzed using the method of characteristics with alternate exit boundary conditions. A steady-pressure outlet best reproduces experimental observations, predicting supersonic efflux, embedded shocks, expansion waves, and circulation production. Several previously unreported unsteady features, including reverse shock or "reshock" formation and embedded shock shedding, are documented. The findings highlight the intricate dynamics of various features associated with such highly transient, blast-driven flows emanating from an open-ended shock tube.