Background-oriented Schlieren technique with vector tomography for measurement of axisymmetric pressure fields of laser-induced underwater shock waves

TL;DR

This paper introduces a novel vector tomography-based background-oriented schlieren technique for accurately measuring axisymmetric pressure fields of laser-induced underwater shock waves, outperforming traditional CT-BOS in several aspects.

Contribution

It proposes a new VT-BOS method capable of reconstructing axisymmetric vector fields with nonzero divergence, improving measurement accuracy and efficiency over existing CT-BOS techniques.

Findings

VT-BOS shows better convergence than CT-BOS.

VT-BOS has lower computational cost.

VT-BOS is less dependent on image resolution.

Abstract

This study aims to overcome the problems that existing background-oriented schlieren (BOS) techniques based on computed tomography (CT-BOS) face when measuring pressure fields of laser-induced underwater shock waves. To do this, it proposes a novel BOS technique based on vector tomography (VT-BOS) of an axisymmetric target. The remarkable feature of the proposed technique is the reconstruction of an axisymmetric vector field with nonzero divergence, such as the field of a laser-induced underwater shock wave. This approach is based on an approximate relation between the projection of the axisymmetric vector field and the reconstructed vector field. For comparison, the pressure fields of underwater shock waves are measured with VT-BOS, CT-BOS, and a needle hydrophone. It is found that VT-BOS is significantly better than CT-BOS in terms of better convergence, less dependence on the spatial resolution of the acquired images, and lower computational cost. The proposed technique can be applied not only to fluid dynamical fields, but also to other axisymmetric targets in other areas, such as electromagnetics and thermodynamics.