Contactless pressure measurement of an underwater shock wave in a microtube using a high-resolution background-oriented schlieren technique

TL;DR

This paper introduces a high-resolution background-oriented schlieren technique for contactless measurement of underwater shock wave pressure fields in microtubes, enabling detailed analysis of shock dynamics and microjet formation at microscale.

Contribution

The study presents a novel high-resolution BOS method capable of measuring narrow shock fronts and pressure impulses at microscale, surpassing previous techniques in spatial resolution and pressure range.

Findings

Measured shock front width as narrow as 101 μm.

Observed linear relation between microjet velocity and shock pressure impulse.

Demonstrated the technique's potential for microscale pressure measurement.

Abstract

A high-resolution background-oriented schlieren (BOS) technique, which utilizes a high-resolution camera and a microdot background pattern, is proposed and used to measure the pressure field of an underwater shock wave in a microtube. The propagation of the shock wave subsequently reaches a concave water-air interface set in the microtube resulting in the ejection of a focused microjet. This high spatial-resolution BOS technique can measure the pressure field of a shock front with a width as narrow as the order of only 101 {\mu}m with a peak pressure as large as almost 3 MPa, which is significantly narrower and larger, respectively, than a previous study [1]. This significant breakthrough has enabled the simultaneous measurement of the pressure impulse of the shock front and the velocity of the microjet tip. As a result, we have experimentally observed the linear relation between the velocity of the microjet tip and the pressure impulse of the shock front for the cases without secondary cavitation in the liquid bulk. Such relation was theorectically/numerically predicted by Peters [2]. This study demonstrated the capability of the proposed high-resolution BOS technique as a microscale contactless pressure measurement tool for underwater shock waves and potentially other micro- and nano-fluids.