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Understanding the kinetic behavior at the scale of a single bubble is crucial for understanding cavitation flow properties. In this study, experiments and numerical analysis of shock waves resulting from the crumpling of a solitary adjacent wall vacuole have been conducted. Shock wave characteristics induced by near-wall bubble collapse were investigated using high-speed photography and shadowgraphy techniques. Numerical simulations were conducted of near-wall vacuole collapse-induced shock-wave dynamics using the OpenFOAM cavitatingFoam solver. (1) The shock wave displays an essentially symmetrical distribution. The pressure maxima diminished along the sagittal diameter. The intensity of the second shock wave generated near the wall was decreased by approximately 21.2% compared to the initial shock wave. The simulated wave speeds exhibit a high level of concordance with the experimental data, and the calculated errors are below 7.9%. (2) The pressure and velocity at which the shock wave propagates in water exhibit a power function and an exponential decay function, respectively, as they travel across distance. And the perturbation profile of the velocity aligned with the direction in which the shock wave propagated. This result indicates that the shock wave acts as a catalyst for the creation of disturbances in the velocity field. (3) Constructing a transformation relation for the wave energy of near-wall vacuole collapse. During its first collapse, the near-wall cavitation bubble lost an average of 85% of its energy. This allowed for the assessment of the erosive impact of cavitation-induced shock waves on rigid surfaces.

Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

Geomaterials (i.e. rock, sand, soil and concrete) are increasingly being encountered and used in extreme environments, in terms of the pressure magnitude and the loading rate. Advancing the understanding of the mechanical response of materials to impact loading relies heavily on having suitable high-speed diagnostics. One such diagnostic is high-speed photography, which combined with a variety of digital optical measurement techniques can provide detailed insights into phenomena including fracture, impact, fragmentation and penetration in geological materials. This review begins with a brief history of high-speed imaging. Section  2 discusses of the current state of the art of high-speed cameras, which includes a comparison between charge-coupled device and complementary metal-oxide semiconductor sensors. The application of high-speed photography to geomechanical experiments is summarized in Sect.  3 . Section  4 is concerned with digital optical measurement techniques including photoelastic coating, Moiré, caustics, holographic interferometry, particle image velocimetry, digital image correlation and infrared thermography, in combination with high-speed photography to capture transient phenomena. The last section provides a brief summary and discussion of future directions in the field.

The morphological changes of leaves under the airflow have a significant effect on the deposition of pesticide droplets on the leaves, but the wind-induced vibration of the leaves is complicated to measure. In this study, an aerodynamic test of the pear leaf was conducted in the wind tunnel, and binocular high-speed photography was used to record the deformation and vibration of the leaves under various airflow velocities. Experiments showed that air velocity ( v ) had a significant effect on the morphological response of the leaf. As v increased, the leaf was in three states, including static deformation, low-frequency vibration, and reconfiguration of airfoil steady state. The mutation from one state to another occurred at the critical velocity of v cr1 and v cr2 . By tracking the leaf marker point, various morphological parameters were calculated, including the bending angle of the petiole, the wind deflection angle, and the twist angle of leaves under different air velocities. When v cr1 ≤ v ≤ v cr2 , the parameters changed periodically. When v < v cr1 , the petiole and the leaf bent statically, and the bending angle of the petiole and the wind deflection angle of the leaf gradually increased. When v > v cr2 , the morphology of the leaf and the petiole was stable. Besides, this study tracked and measured the wind deflection area of leaf, which was consistent with the theoretical calculation results. The measurement of the leaf morphological parameters can reflect the morphological changes of leaves under airflow, thus providing a basis for the decision-making of air-assisted spray airflow.

In this paper, we mainly design two modulation ratios of Al/Ni reactive films, prepare TaN@(Al/Ni) by MEMS (Micro-Electro-Mechanical Systems) technology, and conduct firing experiments using capacitive firing. The experimental results show that the modulation ratio has a large effect on the firing performance of reactive bridge films, and the action process of the reactive film can be clearly observed by high-speed photography.

Sound and light emission by bubbles is studied experimentally. Single bubbles kept in a bubble trap and single laser-generated bubbles are investigated using ultrafast and high-speed photography in combination with hydrophones. The optical observation at 20 million frames per second of the shock waves emitted has proven instrumental in revealing the dynamic process upon bubble collapse. When jet formation is initiated by a non-spherically symmetric environment, several distinct shock waves are emitted within a few hundred nanoseconds, originating from different sites of the bubble. The counterjet phenomenon is interpreted in this context as a secondary cavitation event. Furthermore, the light emission of laser-generated cavities (termed cavitation bubble luminescence) is studied with respect to the symmetry of collapse. The prospects of optical cavitation and multibubble trapping in the study of few-bubble systems and bubble interactions are briefly discussed. Finally, the behaviour of bubble clouds, their oscillations, acoustic noise and light emission are described. Depending on the strength of the driving sound field, period doubling and chaotic oscillations of the collective bubble dynamics are observed.

This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality.

The Invar steel molten pool is characterized by low fluidity of the molten pool due to high tension, which hinders the escape of gases and exacerbates the formation of porosity defects. In this study, the influences of different welding process parameters, material properties, and U-groove on the flow behavior of the molten pool of laser–tungsten inert gas (TIG) hybrid welding of Invar steel are investigated by numerical simulation and high-speed photography. This research proposes effective measures to suppress porosity defects, such as optimizing process parameters and extending the existence time of the molten pool. In conclusion, this study systematically investigates the dynamic mechanism of the formation of welding defects in 4J36 Invar steel and provides important theoretical support for the optimization of the welding process of 4J36 Invar steel. The results indicate that controlling the laser power at 4–6 kW, welding speed at 0.5–1.0 m/min, and welding current at 150–170 A can stabilize the molten pool flow and keyhole and promote the molten pool flow and gas escape.

IntroductionSpread effect is one of the aspects on deposition quality evaluation of pesticide droplets. It could be affected by many factors such as the microstructure of the target plant leaf surface, physical features of the droplets, and the concentration of spray additives.MethodsIn this study, using a high-speed photography system, 2.3% glyphosate ammonium salt solution with different concentration of the additive was applied to investigate the impact process of single droplet deposition on the plant leaf surface with burrs. Effect of droplet sizes and velocities on spreading area and dynamic deposition procedure was analyzed using image processing programs.ResultsThe diffusion factor in the process of droplet spreading was changed over time. The occurrence of bubbles in the droplets was observed in the results. With the bubble generation, the droplet diameter expands and a better diffusion effect is obtained. As a result, better spreading effect was obtained as the droplet diameter was expanded with the generation of bubbles. The significant effects of each physical property of droplets on droplet spreading and the interaction effects between the influencing factors were analyzed. A significant correlation was found between additive concentration, droplet impact velocity, droplet diameters and droplet spreading area. All interactions of concentration:velocity, concentration:diameter, velocity:diameter, and concentration:velocity:diameter had a significant effect on the spreading area of droplets. The study of the factors influencing the process of pesticide droplet impact on the leaf surface contributes to the efficient use of pesticides. Thus, the consumption of pesticides and the resulting impact on the environment can be reduced.

This study presents an experimental investigation into the cavitation flow structures within a water-jet pump, conducted using high-speed photography on a closed-loop test platform. The study captures the temporal evolution of cavitation structures and identifies five typical types: Sheet Cavitation, Cloud Cavitation, Tip Clearance Cavitation, Tip Vortex Cavitation, and Perpendicular Cavitation Vortex (PCV). The evolution of these cavitation structures under varying Net Positive Suction Head available (NPSHa) conditions is analyzed in detail. Based on a combined analysis of cavitation performance curves and flow visualizations, the study reveals that increased cavitation causes the expansion and interaction of PCVs, which block blade passages and result in significant flow separation, ultimately leading to substantial reductions in head and efficiency. Furthermore, the study establishes a quantitative correlation between cavitation vortex structures and pump performance, thereby providing a scientific basis for predicting cavitation-induced degradation. Based on binarized high-speed photography images, the study quantitatively measures vapor volume fractions at various cavitation stages, revealing the relationship between cavitation region expansion and pump performance degradation. It thereby provides visual evidence of cavitation development. This work offers valuable insights into the mechanisms of cavitation evolution and provides engineering guidance for improving the performance of water-jet pumps.