The environmental load can be minimized if the energy of the vibration produced by the tidal current can be obtained as electric power. We investigated the three-dimensional fluttering of the sheet with deflection in the width direction. The Reynolds number Re was varied in the range of 1.24 to 2.01×105 in the direction of flow from the fixed end to the free end of the sheet. The direction of the flow velocity was set as the x-axis and the direction of the gravity as the z-axis. As a result, fluttering with a phase difference was observed in the z-axis direction, indicating that the sheet exhibited three-dimensional fluttering. The frequency of fluttering under the same flow velocity condition was the same at the top and bottom of the free edge of the sheet, but the phase difference in each axis in the time displacement between the top and bottom of the free edge tended to decrease with increasing flow velocity. This may be attributed to the tilting of the vortex structure generated in the sheet against the z-axis direction due to the deflection of the sheet against its initial orientation.

In this study, a tidal current energy is focused in ocean-based renewable energies. Collecting a tidal flow is very important because it is generally known that a power available from a stream of water is proportional to the cube of the free stream velocity of the current. In this research, a bi-directional turbine system is investigated for a tidal flow that changes the direction periodically. Numerical investigations are conducted on a bi-directional flow collector with guide vane to collect the flow, in which the effects of vane skew angle and blade number are investigated. Calculated results showed that the collector with eight guide vanes was the highest angular moment at turbine inlet. The axial velocity at turbine inlet was larger for smaller value of the vane skew angle, whereas the tangential velocity at the turbine inlet was larger for larger value of the vane skew angle. As the results of both the profiles of axial and tangential velocity, the angular moment took the local maximum value at around the angle of 180 deg. in this study.

This paper aims to conduct PIV (Particle Image Velocimetry) measurement of oscillatory flow in the complex structure of human bronchus model. In this experiment, human respiration was simulated as a sinusoidal flow. The sinusoidal flow was generated by the plunger movement of syringe. The flow rate of the oscillatory flow was simulated as sinusoidal cycle. The oscillatory flow simulated resting human respiration (Re=1415, 20 breaths per minute). Human bronchus model was made of transparent silicon. A bent pipe was connected to the human bronchus model to simulate larynx. To match the refractive index of silicon model, glycerol aqueous solution (50% volume of glycerin) was used as working fluid. Microbubbles were used as tracer particle of the PIV measurement. YAG laser was used to illuminate the tracer particle. The PIV measurements were conducted in 3 areas which were around the bifurcation of the trachea. Phase averaged velocity profiles were calculated in 16 phases of sinusoidal cycle. As a result, velocity fields involving flow separations were measured. This result indicates that the adverse pressure gradient occurs in branch region and curved region of the bronchus model at inspiration part. It is found that the separation flow does not occur at expiration part.

The wing of a dragonfly does not have a streamlined shape like an airplane, but has a unique shape with irregularities. This shape is called a corrugated wing and is known to have excellent performance with a low Reynolds number. In this study, we measured the wake distribution in the low Reynolds number region and analyzed the frequency using a circulating water tank, and compared it with the camber blade.

Blue-green algae (Cyanobacterial blooms) appear on the surface of eutrophicated lakes and marshes in the intensified solar radiation season, especially in the summer. Cyanobacterial blooms are a phenomenon in which specific aquatic cyanobacteria such as Microcystis, a unicellular organism, emerge and accumulate at high density. The kinematic viscosities of the surface water covered by cyanobacterial blooms appear shows two times higher than that at 0.3m below the surface. The water with accumulated cyanobacterial blooms can be treated as a non-Newtonian fluid due to their viscous biofilm.

In recent years, regenerative medicine has been being developed due to the improvement of tissue engineering, e.g. autologous regenerative tissue by three-dimensional culture. In this study, Ultrasound-assisted Doppler Velocigraphy (UA-OCDV) is constructed to measure the mechanical properties of regenerated tissues, tomographically, non-contactly and non-invasively at the micrometer resolution. This is based on Doppler OCT, which can visualize Doppler velocity inside tissue by applying phase analysis to low coherence interference signals. Furthermore, an ultrasonic transducer is introduced into Doppler OCT as a non-contact loading device of periodical acoustic radiation pressure. UA-OCDV was experimentally applied to agar-embedded non-woven fabrics as a sample. As a result, UA-OCDV was able to provide the tomographic visualization of Doppler velocity and vibration phase, caused by the acoustic radiation pressure. The propagation of shear wave was visualized according to the spatio-temporal fluctuation of Doppler velocity. The propagation phase, associated with tissue elasticity, was observed to delay from the focal point of radiation pressure to the fixed sample edge. In conclusions, it was suggested that UA-OCDV had a potential of diagnosing the mechanical properties of regenerative tissue non-contactly and non-invasively.

The effect of the nozzle throat height (HNT) on the buzz characteristics, which occurs on the ramjet engine for High Mach Integrated Control Experiment (HIMICO), is experimentally studied. The ramjet engine is composed of a variable rectangular intake, a combustor and a variable nozzle. The freestream Mach number of the wind tunnel is set at 3.4. The unsteady static pressure inside the intake is measured and the movement of the shock waves are visualized by the Schlieren imaging. Results show that the frequency of the buzz increases with the decrease of HNT. The temporal change of the static pressure shows that the smaller HNT accelerates the rise of the static pressure, but it does not affect the reduction speed. Therefore, it becomes clear that the cause of the buzz frequency change is the rising speed of the static pressure. Results of the pressure measurement also show that the minimum value of the static pressure inside the intake is not affected by the value of HNT. The results of the Schlieren imaging suggests that the shock wave structure when the leakage diminishes is the same regardless of the value of HNT. The static pressure inside the intake is mainly determined by the shock wave structure at the entrance of the intake and the free stream condition, so the value of the minimum static pressure does not depend on HNT.

Flow fields around a re-entry or entry body flying at high altitudes in planetary atmospheres with hypersonic velocities tend to be in thermochemical nonequilibrium states due to the fact that the characteristic times of vibrational excitations and chemical reactions behind strong shock waves become comparable to those of fluid flows. In order to simulate such thermochemical nonequilibrium flows, Casseau et al. (Aerospace, 3(4), (2016), 45) have recently developed a numerical code hy2Foam based on OpenFOAM. In the present work, we have conducted numerical simulations of thermochemical nonequilibrium flows around spherical projectiles launched by a ballistic range in order to validate hy2Foam. The results show that hy2Foam can predict the shock standoff distances within the accuracy from 2 to 10 % under the conditions of the present simulations.

Considering the heat input and the resulting density change, the mass flow rate of liquid oxygen was predicted and compared to the results of cold flow tests. The prediction error of the flow rate was within 2 % assuming a constant heat transfer coefficient. Temperature rise between the tank and the injector manifold located at the exit of the piping system was also well explained by the suggested model. The discharge coefficient of the injector was found to be constant (Cd=0.66) at a mass flow rate larger than 120 g/s but became smaller at a lower mass flow rate. At a deep throttle condition (less than 10 % of the full throttle), vaporization of oxygen occurs at the injector manifold and the predicted mass flow rate was significantly deviated from the experimental result.

The present study analyses the bundle features of vortical axis-lines in an isotropic homogeneous turbulence in Direct Numerical Simulation (DNS). The vorticity line and eigen-vortical axis line defined by the real eigenvector of the velocity gradient tensor are analysed in terms of the geometrical characteristic in the vortical region. We apply the theory of local axis geometry that specifies quantitatively the characteristics of the bundle of axis-lines with respect to the passage of vortical region. The analysis method focuses on the gradient tensor of the subjected vector field with respect to the swirl plane and evaluates the physical quantities such as swirlity and sourcity that specify the unidirectionality and the intensity of the respective azimuthal and radial vector (flow) components in the swirl plane. The bundles and distributions of these vectors of the two lines show that the most of eigen-vortical axis lines do not have swirling feature whereas the vorticity lines swirls. While the vorticity lines or vorticity vector have an effect of the vortex stretching to swirl, the relationship between the two vectors of these lines in the swirl plane, expressed as a linear transformation, seems to restrain swirling of the eigen-vortical axis line.

The phenomenon of super-synchronous rotating cavitation (super-S RC) has been observed in liquid rocket inducers. This phenomenon is known to induce axial oscillations of about 1.2 times the inducer rotation speed. Tsujimoto et al. have investigated in detail the region where super-S RC occurs when the flow rate and cavitation number are varied, but the mechanism has not been fully elucidated. In this study, the oscillation characteristics of the cavity in the inducer were evaluated by numerical analysis at several rotation speeds using general-purpose software. The results showed that the cavity frequencies of equal length cavitation (EC) and super-S RC were continuously monotonically decreasing, while the cavity frequencies of synchronous rotating cavitation (sync RC) and cavitation surge (CS) were not monotonically decreasing. Furthermore, the maximum cavity length was found to be independent of the rotation speed. A comparison of the Strouhal number using the cavity length showed that the Strouhal number was almost equal not only for EC and super-S RC, where the cavity frequency was continuously monotonic, but also for sync RC, which deviated from the monotonic decrease. On the other hand, the Strouhal number in CS was discontinuously high. This indicates that the super-S RC and sync RC, which are locally unstable, and the EC, which is stable, share the same cavitation characteristics, while the CS, which is system unstable, has distinctly different characteristics.

The use of nitrous oxide as a propellant is one of the most effective options for simplifying and improving the operability of rocket engines for launch vehicles and spacecrafts. On the other hand, when nitrous oxide is supplied with self-pressurization, a gas-liquid two-phase flow with strong unsteady characteristics is formed, and it is difficult to accurately predict the flow characteristics. In this paper, the outline of the newly developed capacitance void fraction meter was reported. The void fraction was successfully measured by calibrating the void fraction meter using the results of the subcooled nitrous oxide flow tests. As a result, in our test condition, it was found that the void fraction of the gas-liquid two-phase flow caused by self-pressurization was 0.2-0.6 and there was a tendency to increase unsteady.

As an attempt to investigate the effect of acetone droplets on methane/air laminar premixed flame behavior such as laminar flame speed, Markstein length, and flame structure, two-dimensional direct numerical simulations (DNS) are performed under different conditions of equivalence ratio and phase of acetone. The result suggests that the evaporation of acetone droplets increases flame instability and inhibits the increment of laminar flame speed.

In order to establish a method for evaluating fluctuating aerodynamic noise, the active turbulence generator was fabricated, and wind tunnel experiments were conducted. A side-view mirror model was set for several flow conditions, and the aerodynamic noises emitted by the model were measured with a microphone. The general spectrum analysis as well as modulation power spectrum analysis were performed on the measured sound. As a result, the general spectrum analysis could not represent the difference in aerodynamic noise at different mainstream turbulence. In contrast, the proposed modulation power spectrum showed that it is possible to represent the spectral intensity and the difference in power of the sound in the modulation frequency band. The future works are to study how to correct the modulation power spectrum by band and how to integrate it in a frequency band, and how to define the sense of fluctuation in auditory tests.

An adjoint sensitivity analysis method based on the lattice Boltzmann equation was developed for flow-induced sound problems. In this method, flow and acoustic fields around complex geometries are directly simulated using the lattice Boltzmann method (LBM) with the interpolated bounce-back (IBB) condition. To efficiently evaluate sensitivities of numerous design variables for flow-induced sounds, adjoint equations for the LBM with the IBB condition was formulated. These adjoint equations can be easily computed, similar to the LBM. This method was validated through a minimization problem of the Aeolian tone generated from a bluff body in uniform flow. Consequently, sensitivities evaluated by the adjoint method agreed well with those evaluated by the finite difference method. The results suggest that the proposed method is useful for shape optimizations intended to reduce flow-induced sounds.

This study investigated the phenomenon that a square prism, which is one of the structural elements, vibrates in the flow direction. By attaching a control plate to the corner of the surface of the prism, the vibration was controlled by a method of controlling the flow of separation from the object. In the experiment, the test model was installed in the in-line free vibration experimental device in the wind tunnel, and the fluid dynamic response characteristics were investigated by changing the length and mounting method of the control plate in various ways. In addition, the length and mounting method of the control plate that effectively suppresses the occurrence of vibration were examined. The test model is elastically supported at it's both end and is restricted to vibrate in only in-line direction. Instantaneous displacement of test model was measured by means of Laser Displacement Anemometer, and degree of vibration was evaluated by rms value of the fluctuating displacement. As a result, it was found that the vibration effect obtained differs depending on the mounting method, length, and angle of attack of the control plate. Therefore, the method used in this study can suppress the displacement of flow-induced vibration in the inline direction.

In this study，the flow-induced vibration phenomena on a cylindrical structure at snow and ice accumulation were investigated．Specifically，a cylindrical structure with snow and ice on it was modeled and three models of different sizes were examined．The free vibration experiments were conducted in a wind tunnel to investigate the fluid dynamic response characteristics of cross-flow flow-induced vibration．The relationship between the reduced mass-damping parameter and the maximum displacement was also investigated in the experiments．In addition，the flow patterns during stationary and oscillatory conditions were investigated by conducting a water channel visualization experiment．As a result，the maximum displacement of the flow-induced vibration in the snow and ice accretion model were found to be much larger than that of a circular cylinder．The relationship between the size of the snow/ice accretion and the maximum displacement of the flow-induced vibration and the reduced mass-damping parameter were clarified．Furthermore，the relationship between the vortex formed around the object and the vibration phase was clarified．

We proposed prediction methodology of broadband noise generated from a low-pressure fan based on the pressure power spectrum density (PSD) of a flat plate determined experimentally. Although the predicted broadband noise by the pressure PSD was evaluated 12.5 dB larger than the measured value, it could represent the measured spectral distribution. In the tip side of the blade, even if the relative velocity of the wake decreased, the broadband noise of its blade element was larger than the mid span domain where the relative velocity was high. We indicated that the increase of the broadband noise at the blade tip was due to the normalized pressure PSD became larger than that one at the mid-span.

The far-field sound generated aerodynamically from a box fan is predicted by a computational aeroacoustics (CAA). The method is composed of the large eddy simulation of the incompressible fluid flow that computes the transitional boundary layer on the fan blades and the wake and the acoustical simulation that takes the effects of the reflection of the sound radiated from the fan into account. In particular, the influence of the Sub-grid scale (SGS) model on the computed flow field and that of the position of the dipole sound source on the radiated sound are investigated. The far-field sound spectra computed by the above-mentioned method are compared with the measured ones as well as that computed by the Curle’s equation. It is found that the Dynamic Smagorinsky Model predicts the far-field sound more accurately than the Standard Smagorinsky Model. The position of the dipole source affects remarkably the far-field sound.

In this study, to investigate the effect of inflow turbulence on the flow structure around the wing tip, static pressure fluctuation around airfoil was measured when the inflow turbulence was changed with five types of turbulence grids. The model had the NACA0012 wing section, chord length of 60 mm and a wingspan length of 120 mm. The Reynolds number based on the chord length and inflow velocity was 1 × 105, and the angle of attack of the wing was 13 °. The measurement range was 20 mm × 20 mm at the position of X/C = 1.47 with the mainstream direction as X from the leading edge of the wing. In the test section, the airfoil was vertically installed and the pressure probe was installed in the flow from downstream of the airfoil. As a result, the region with high static pressure fluctuation was distributed from the center of the tip vortex to the outside when the turbulence intensity and turbulence length scale were low, but it also spread to the center of the vortex as they increased.

Accurate flow rate measurements are required in many industrial plants. The flow rate for feedwater is one of the important parameters in many power plants. Therefore, evaluation of existing flowmeters is sometimes required. One of the effective solutions to measure the flow rates in existing pipes is to use clamp-on ultrasonic flowmeters that the ultrasonic sensors are installed at designated points external to the piping system. To improve the measurement accuracy, parallel multiple measuring lines have been generally employed for in line type ultrasonic flowmeters. However, it is difficult to set the sensors on parallel for the clamp-on type. Therefore, we focused on an ultrasonic tomography method that reconstructs the flow velocity distribution using multiple measurement lines. In the tomography method, ultrasonic is emitted with wide-divergence angle and the signal is received at several sensors. In this study, we analyzed the ultrasonic propagation in a 100A pipe to confirm the effectiveness of the tomographic flow measurement method.

A method for identifying the flow regimes of gas-liquid two-phase flow using ultrasound was developed in this study. The method of analyzing the gas-liquid two-phase flow rising in a vertical pipe can be applied to the sequential measurement method in an airlift pump which is used for pumping rare earth resources existing in the deep sea bottom. The distributions of the ultrasound echo intensity and velocity calculated from Doppler frequencies are output as image data with the distance from the ultrasound transducer and profiling time as the two axes, and the images are processed using various filters. The results suggest that it is possible to distinguish between small and large bubbles by focusing on the reflection intensity obtained from the region behind the bubbles on the measurement line and the flow velocity after the passage of the bubbles. By identifying between small and large bubbles, the void fraction, which is an index of the flow regimes, was calculated from the echo data. On the other hand, it remains a challenge to set appropriate thresholds for various objects and environments and to evaluate them quantitatively. Thus, we also attempted to classify bubbly flow and slug flow by using machine learning on the image data.