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

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 $$10^1\,\upmu$$ 10 1 μ m with a peak pressure as large as almost 3 MPa. 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 theoretically/numerically predicted by Peters et al. (J Fluid Mech 719:587–605, 2013). 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 nanofluids. Graphical abstract

Background-Oriented Schlieren technique using Fast Checkerboard Demodulation for extending measurement range of pressure of underwater shock waves

“…Therefore, extension of displacement detection range under high spatial resolution will directly extends the pressure measurement range. This is confirmed by the data collected in our study which have a shock wave pressure up to 20 MPa, exceeding the measurement limit of 8 MPa by Yamamoto et al (2018). When the maximum displacement is larger than 10 µm, the maximum displacement detected by the FCD is 10 µm because FCD detects displacement from frequency change by Fourier transform in the range of phase from -π to π.…”

“…BOS technique using Digital Image Correlation (DIC-BOS) with a randomly dotted background image was applied by Yamamoto et al (2015) to measure laser-induced underwater shock waves. It was further developed by Yamamoto et al (2018) into high resolution DIC-BOS which has successfully measure underwater shock wave pressure up to 8 MPa. Apart from DIC-BOS, BOS technique using Optical Flow algorithm (OF-BOS) was utilized by Hayasaka et al (2016) to measure the pressure field of millimeter-scale laserinduced underwater shock wave.…”