In wake galloping of two square prisms of same size, irregular vibrations have been reported to occur in certain configurations. However, the time-varying characteristics of the vibrational displacement have not been clarified in many cases. In this study, we aimed to clarify the relationship between the flow pattern and the increase or decrease of the vibration displacement in local time, and conducted visualization measurements using a water channel and a forced vibration experiment under conditions in which irregular vibrations occur. As a result, it was confirmed that there are flow conditions in which one period of vibration does not correspond to one period of flow pattern, and that there are differences in the vortices formed by large and small displacements.

In order to develop microphone array for the wavenumber-frequency spectrum analysis that separates the hydrodynamic pressure fluctuations (HPF) and acoustic pressure fluctuations (APF), it is necessary to consider the spatial resolution to capture both eddy scale of the turbulent flow and wavelength of the sound which has relatively large scale compared to the flow eddy. In this study, the effects of the number of microphones and their arrangement on the accuracy of the analysis were investigated, and the optimized microphone array arrangement was explored. The results of comparison of the wavenumber-frequency spectrum indicated that the microphone array with a well-balanced combination of sparse and dense microphone arrays (such as the logarithmic spiral array and localized random array) of 96 channels or more is required to separate APF and HPF in the frequency band of 500~5 kHz which is required for the analysis of automobile aeroacoustics noises.

Interior noise reduction is an important issue for motorcycle helmet quality. In this study, the relationship between the flow field outside the helmet and the internal noise was investigated for wind noise, and the aerodynamic sources that causes the internal noise were explored. Numerical simulation confirmed that the formation of vortices around the helmet. The acoustic field was generated at the point where the vortex convection caused by the detachment and reattachment of the flow, suggesting that the pressure fluctuation caused by the vortex formation contributed to the sound generation. Based on these numerical results, was experimentally measured using the coherent output power. As a result, strong correlations were confirmed among the shield, neck, and forehead/occipital projection areas. In particular, the shield and neck areas significantly contributed to the internal sound. The shield part is a stagnation point and the pressure fluctuation was small, suggesting the possibility of self-excited vibration with the hinge of the shield, while the neck part is thought to transmit internal sound due to pressure fluctuation caused by detachment and reattachment of the flow.

It is necessary to reduce the aerodynamic sound generated by fans since they are often used for air-conditioner, which are placed in human living areas, such as homes and offices. To reduce the aerodynamic sound, we focused on the Helmholtz resonator (HR). Toward developing HR that can be installed into air-conditioners and reduce aerodynamic sound, the present study investigated a numerical analysis method and the effect of cavity shapes on the sound reduction performance of HR using a simple computational model. As a numerical analysis method, we used the lattice Boltzmann method (LBM), which can simultaneously simulate aerodynamically sound generation in fans and the acoustic resonance in resonators. First, the capability of the LBM to simulate acoustic resonance was validated. As a result, it was shown that the calculation results were consistent with the theoretical equation. Furthermore, the present study revealed the relationship between the depth of the resonator cavity and the sound reduction effect.

In this study, aerodynamic noise generates from forward step flow with different flow velocities U₀ and step heights H were measured to investigate the characteristics of high-frequency wind noise generated from the Forward-Facing Step. The flow velocity was set to 0~50 m/s and the step height to H = 15, 30 and 45 mm. The aerodynamic noise was converted into sound pressure spectra by FFT to investigate their characteristics. To investigate the influence of the boundary layer thickness δ and step height H on the shear layer of the step, correlation measurements were performed on the shear layer to estimate the vortex scale. The results show that the high-frequency aerodynamic noise has a characteristic peak that is independent of the flow velocity. It is also confirmed that vortex scales which are nondimensionalized by step height generated in the shear layer at H/δ = 2 and 3 is similar.

Fluctuating aerodynamic noise, that is, time-varying wind noise can significantly affect driver annoyance during at high cruising speed, independent of average loudness. Causes of fluctuating aerodynamic noise include wind buffeting generated by other vehicles, and also wind gusting. Therefore, it is necessary to clarify the generation mechanism of the fluctuating aerodynamic noise generated in the turbulent flow. In the uniform flow without turbulence, our previous study has revealed the generation mechanism as well as noise sources of aerodynamic noise on the longitudinal vortex system. In the experimental and numerical study, turbulence was produced with a cylinder placed upstream of a delta wing. Main flow with periodic turbulence of Karman vortex impinged with the longitudinal vortex system generated along the leading edge of the delta wing. The study was conducted experimentally and numerically. Both the studies showed that aerodynamic noise is amplified around the frequency of shedding vortices. The numerical data was also investigated with modulation spectrum analysis. As a result, it was found that the shedding frequency is modulated to the lower frequency range related to fluctuating aerodynamic noise.

Cup transport systems are machines that print on plastic cup, and air nozzles are used to separate, hold, and release the cup. Since air nozzles release high-pressure air into the atmosphere, fluid noises, e.g. 96.3dB from printing mandrel part and 90.8dB from supply spiral nozzle, are generated by the air jet, and it cause to worse work environment. The purpose of this study is to investigate the noise characteristics of the supply spiral nozzle (actual nozzle) used in a cup transport system and to take measures to reduce noise. In the experiment, compressed air was supplied from an air compressor, and the noise level, cup flying distance, and jet velocity were measured. As a result, it was found that the noise level of the actual nozzle tends to become large as the downstream direction, and that the noise was greatly affected by the jet flow from the outer hole compared with that from inner hole. It was also found that the noise increased in proportion to the 4.5th power of the jet velocity and the 4th power of the equivalent diameter of the jet outlet. As a result of the noise reduction measure, 5dB of noise was reduced by using the nozzle with hole diameter of 0.8mm and 6 holes.

At the orifice of a Helmholtz resonator attached on a duct, acoustic resistance increases with the grazing flow speed. When the orifice corners are rounded, the increase in acoustic resistance due to the grazing flow is suppressed compared to when the orifices are right-angled. In this study, CFD analyses on the flow field including pressure fluctuation were performed for a resonator with right-angled orifice corners (NN model) and for a resonator with rounded orifice corners (RR model). The increase in acoustic resistance obtained from the CFD analysis qualitatively agrees with the previous experimental results; Acoustic resistances of both models are almost same when the grazing flow is slow. In contrast, when the grazing flow is fast, the acoustic resistance of the RR model is about half compared to that of the NN model. Moreover, Acoustic powers at cross sections normal to longitudinal direction of the duct were calculated by integrating acoustic intensity considering the effect of time averaged flow. The acoustic powers upstream and downstream of the resonator are both almost uniform, respectively, except the region in which the acoustic intensity is highly disordered. The difference in the acoustic powers at two sections upstream and downstream of the resonator coincides with the acoustic energy consumption rate calculated by using the acoustic resistance and particle velocity through the orifice. This shows that the acoustic resistance value estimated from the transfer function of sound pressures measured at two microphone positions is plausible.

In general, flexible plastic wings are the primary components of small lightweight aircrafts such as unmanned aerial vehicles (UAVs). One of the authors has shown that the torsional oscillation of a plastic wing occurs in a certain range of its attack angle, which causes a rise in lift of the wing. However, the conditions under which the wing exhibits the high-lift characteristics remain unclear. To find out the conditions, the aerodynamics characteristics of the wing are experimentally investigated by changing its rigidity and aspect ratio under various flow speeds in the wind tunnel. The experimental results reveal that the aerodynamic characteristics of flexible wing are dominated by the two dimensionless parameters which are derived from the equation governing the torsional oscillation of the wing.

The goal is to achieve a stable supply of electric power, reduce environment footprint, simplify maintenance. We focused on the circulating flow generated by vibrating a flexible tube containing liquid to uses ocean energy. In this study, we investigated the mechanism of vibration induced circulation flow. As a result, the length of lC can contribute to increase the flow rate. The same phenomenon occurs repeatedly in the observed waveforms.

In the decommissioning process of the Fukushima Daiichi Nuclear Power Plant of the Tokyo Electric Power Company, Incorporated (TEPCO), it is necessary to investigate the leakage area of coolant and so on. We have focused on ultrasonic measurement as an investigation method to supplement optical measurement methods such as cameras.In this study, we have developed and verified a measurement system using ultrasonic velocity distribution measurement and ultrasonic environmental measurement to measure the velocity distribution in a wide area and to estimate the leakage point in unknown underwater environment, aiming to apply the measurement method to a robot for the investigation in the reactor during the decommissioning work process.