We build an ultra-high-speed imaging system based on the background-oriented schlieren (BOS) technique in order to capture a laser-induced underwater shock wave. This BOS technique is able to provide two-dimensional density-gradient field of fluid and requires a simple setup. The imaging system consists of an ultra-high speed video camera, a laser stroboscope, and a patterned background. This system takes images every 0.2 $μ$s. Furthermore, since the density change of water disturbed by the shock is exceedingly small, the system has high spatial resolution $\sim$ 10 $μ$m/pixel. Using this BOS system, we examine temporal position of a shock wave. The position agrees well with that measured by conventional shadowgraph, which indicates that the high-speed imaging system can successfully capture the instantaneous position of the underwater shock wave that propagates with the speed of about 1500 m/s. The local density gradient can be determined up to $O$(10$^3$ kg/m$^4$), which is confirmed by the gradient estimated from the pressure time history measured by a hydrophone.
Forward and inverse modeling of depth-of-field effects in background-oriented schlieren
Pennsylvania State University（宾夕法尼亚州立大学）；University of Texas at San Antonio（德克萨斯大学圣安东尼奥分校）；Office National d’Études et de Recherches Aérospatiales（法国国家航空航天研究局）
Flow over an espresso cup: Inferring 3D velocity and pressure fields from tomographic background oriented schlieren videos via physics-informed neural networks
High-resolution pressure imaging via background-oriented schlieren tomography: a spatiotemporal measurement for MHz ultrasound fields and hydrophone calibration
Unified Deflection Estimation and Error Analysis for Background-Oriented Schlieren
Institute of Fluid Mechanics & Aircraft and Propulsion Laboratory, Ningbo Institute of Technology, Beihang University（北京航空航天大学宁波理工学院流体机械与航空推进实验室）；Tianmushan Laboratory（天目山实验室）
Estimating density, velocity, and pressure fields in supersonic flow using physics-informed BOS
Pennsylvania State University（宾夕法尼亚州立大学）；CSIR-National Aerospace Laboratories（印度国家航空航天实验室）；Case Western Reserve University（凯斯西储大学）；National Research Council Canada（加拿大国家研究委员会）
