Measurement of traveling pressure waves inside a droplet

TL;DR

This paper introduces a novel background-oriented schlieren (BOS) technique with ray-tracing correction for precise measurement of shock wave interactions inside droplets, validated by experiments and numerical simulations.

Contribution

The study develops and validates a new BOS method for quantitative, high-resolution measurement of shock wave-droplet interactions, including phase shifts, with improved accuracy.

Findings

BOS technique accurately measures shock wave dynamics inside droplets.

Quantified density and pressure fields agree with numerical simulations.

Successfully captures phase shifts before and after shock focusing.

Abstract

Shock wave-droplet interactions have been receiving increasing attention due to their relevance in aviation fuel combustion and minimally invasive medical treatments, yet quantifying them experimentally remains a challenge. In this study, we propose a background-oriented schlieren (BOS) technique for quantitative spatiotemporal measurements of shock wave-droplet interaction, employing a novel ray-tracing correction, a synchronization system, and a projected background. Underwater shock waves propagating both inside and outside a millimetric perfluorohexane droplet immersed in water are experimentally measured. The quantified density-gradient and pressure fields are compared with numerical simulations, and the BOS measurements-including sound speeds, the shock-focusing location, and the maximum pressure-are found to be in close agreement with the numerical results. Notably, the technique successfully captures the phase shift before and after shock focusing that had previously only been hypothesized.