This study was aimed at integrating the microchip laser-induced breakdown spec-troscopy (LIBS) technology with air-coupled ultrasonic technology to construct a three-dimensional (3D) element mapping system that can rapidly determine the posi-tion, shape, and surface element composition of objects. First, the working principles of the microchip-LIBS system and air-coupled ultrasonic system for shape measure-ment and solid–liquid surface differentiation were examined. Subsequently, a 3D el-ement mapping system was developed by integrating the microchip LIBS and air-coupled ultrasonic systems. The primary application of this system is expected to be the assessment of nuclear fuel debris in nuclear reactors. Thus, experimental validation was performed using simulated nuclear fuel debris in a mist environment. The 3D element mapping system successfully established a 3D element map containing information regarding the location, shape, and surface element composition of the nuclear fuel debris samples. Moreover, ultrasonic measurement helped clarify the shape and position, while also predicting the solid and liquid surfaces of the simulated fuel fragments. This information helped enhance the efficiency of microchip-LIBS measurement. Furthermore, the microchip-LIBS system could effectively determine the elemental composition on the surfaces of the simulated nuclear fuel debris and optimize the shape measurement results of the ultrasonic system. Overall, the integration of these two systems enables more effective and accurate determination of the shape, position, and surface element composition of nuclear fuel debris.

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Using experimental and numerical results, this paper describes the effects of tabs on the flow characteristics of a plane jet at comparatively low Reynolds numbers while focusing on the velocity field and the vortical structure. The flow visualization and velocity measurements were respectively carried out using laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). In addition, three-dimensional (3D) numerical simulations of a plane jet were performed using ANSYS Fluent, a commercially available computational fluid dynamics (CFD) software application. We found that the spreads of jets perturbed by large delta tabs and round tabs are larger than those produced by the other tabs tested. Additionally, it was determined that a plane jet with square tabs has the smallest jet spread downstream, and the jet’s centerline velocity is maintained in comparison with those of jets perturbed by the other tabs. It was also observed that the spanwise large-scale vortical structure of a plane jet with tabs disappears completely. Good agreement is found between the experimental and numerical simulation velocity profiles in the area near the nozzle exit when the laminar flow model is used. However, we also found that large eddy simulation (LES) is better at predicting the developing flow field of a plane jet than the laminar and the standard k-ε turbulence models.

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This paper presents a newly developed experimental method for measuring the impact force of a rain droplet on the leading edge of a wind turbine blade under rain erosion conditions. A piezoelectric pressure sensor, calibrated against a force sensor using the pulsed jet apparatus, was installed on the leading edge of the wind turbine blade to measure the impact force. The pressure sensor’s output signal was transmitted to a computer system using a wireless signal transmission. The experimental results obtained from a rain erosion tester revealed that the impact force of a droplet with a diameter of 2.4 mm, impacting the leading edge of the rotating blade, generated an impact force of 82.7N at a velocity of 127 m/s. This measurement closely agreed with the numerical result of impact force obtained from the incompressible Navier-Stokes equations within an experimental uncertainty, indicating the validity of the proposed experimental method.

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Ablation phenomena due to aerodynamic heating were experimentally studied using a spherical model made from ice in the Mach 7 hypersonic wind tunnel at Kashiwa campus, the University of Tokyo. A series of experiments conducted so far is re-viewed, with a focus on characteristic features of shape changes over time. Detailed observations were made of recession of the surface due to melting, re-freezing into ice columns like frost pillars in the outer edge region, spallation of small ice particles released from tips of ice columns, and fragmentation into relatively large blocks of ice with a massive puff of water mist. Spin motion of the ice model around its center axis and a method for shape change control were also experimentally demonstrated. Results from ice ablation experiments give us useful insights for designing thermal protection systems of atmospheric entry vehicles, for understanding phenomena occurring around meteorites, and so on.

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In a subsonic free jet, vortex sound is generated at the end of the potential core, but the mechanism of generation of that sound is still unclear. A recent study proposed that pressure waves propagating upstream in the jets interact with Kelvin–Helmholtz (K–H) instability waves, possibly creating a feedback loop that intensifies (Bogey, 2021). In this study, we applied total a least squares dynamic mode decomposition (TlsDMD) to the time series of the numerical results of an axisymmetric subsonic free jet and per-formed a detailed analysis of this hypothesis. We extracted the DMD mode at the K–H instability frequency, i.e., the dominant frequency peak near the nozzle exit. The find-ings indicate that this DMD mode contains not only K–H instability waves but also the pressure waves propagating upstream in the jet. Second, we applied a spatiotemporal Fourier analysis to the DMD mode to describe the characteristics of the pressure waves and confirmed that the pressure waves originate at the end of the jet potential core and that a feedback loop exists at the K–H instability frequency. Our results support this feedback mechanism for sound generation in subsonic free jets.

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In this paper, a method for pneumatic control of aerostatic bearings is examined by numerical simulation. A pneumatic control system using a pneumatic pilot valve, and a nozzle flapper was proposed to realize inexpensive and simple pneumatic control. A numerical model of an aerostatic spindle was developed to investigate the characteristics of the pneumatic control system. The aerostatic spindle was considered as a spring mass damper model, and the stiffness and damping coefficients were calculated using the compressible Reynolds equation and the perturbation method. The calculation results show that the proposed pneumatic control system can increase the machining accuracy of the aerostatic spindle. By setting the gain of the pneumatic control system appropriately in relation to the rotor rotational speed, it was possible to counteract the phenomenon that deteriorated the machining accuracy.

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The power performance of a waterfall crossflow hydraulic turbine was numerically investigated by solving the unsteady Reynolds averaged Navier–Stokes equations combined with the volume-of-fluid method. In this study, characteristic parameters such as the tip-speed ratio, offset distance, and number of blades were investigated numerically to improve the power performance of the hydraulic turbine. Two optimum conditions were obtained in this study: one was the operation at mid-offset distances of 0.35–0.43, and the other was that at a large offset distance of 0.48, which is the condition of flow impact near the blade edge. The former operation yielded a peak efficiency at a tip-speed ratio of approximately 0.7. The peak value slightly increased with an increase in the number of blades. However, the latter operation resulted in a peak efficiency at a lower tip-speed ratio of 0.6, and it sharply increased with an in-crease in the number of blades. This latter feature could be caused by the operation at the optimum inlet angle to the blade at an offset distance of 0.48, where the lift force contribution was clearly observed in the flow field.

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Nuclear power plants use high-temperature, high-pressure steam and cooling water for power generation, which generates high-speed fluid flow in the piping, resulting in erosion and corrosion of the piping during operation. Therefore, regular inspections for pipe-wall thinning are essential. On the other hand, since there is a large amount of piping to be inspected, it is desirable to introduce more efficient inspection methods to improve the economic efficiency of nuclear power plants. This paper introduces the standards related to the wall-thinning inspection in nuclear power plant piping, as well as technologies that are close to practical application in the inspection of the pipe-wall thinning: a wireless ultrasonic sensor, a high-temperature thin-film ultra-sonic sensor, a pulsed eddy current testing method, an electromagnetic acoustic transducer, and a dry-coupled ultrasonic sensor. The main features of each technology are outlined with appropriate citations.

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