Hiroshi Yokoyama

• Doctor of Philosophy (Engineerng)
• Professor at Toyohashi University of Technology

CO2-separation technology is required in various industrial plants to reduce CO2 emissions. A method for promoting adsorption via acoustic excitation is proposed, and the effects of acoustic excitation on CO2 physisorption are investigated using a monolith coated with zeolite. The monolith is placed in a flow duct, where a CO2 + N2 gas mixture is f...

Expanding pipes with orifice plates are often utilized as silencers for fluid machinery. However, intense tonal sounds can be generated from a flow through such expanding pipes. To clarify the mechanism of tonal sound from a flow through a circular expanding pipe with two orifice plates and the conditions for intense acoustic radiation, the flow an...

In automatic transmissions, hydraulic oil in the oil sump is strongly agitated by gears during operation; thus, the oil is mixed with great amounts of air. Air-mixed oil is sucked and discharged by a hydraulic pump to shift the gears. Although air bubbles mixed in the oil may affect the behavior of the rotors, driving torque, and discharge flow rat...

The mouthpiece geometry of single-reed instruments has been known to have a great impact on sound quality and playability. Although many researchers have investigated the effects of the geometry using artificial blowing machines or user case studies, few attention has been paid to the essential cause of physical changes in the instrument. In this s...

Loop-Heat-Pipes (LHPs) are promising for cooling of electric devices in spacecraft. However, the LHP operation must be shut down in some cases (e.g., lunar rover on cold nights) to avoid overcooling or reduce heater energy consumption. In this study, we placed an electrohydrodynamic (EHD) conduction pump in the liquid line of the LHP, which operate...

Single-reed instruments produce sounds with fluid-structure-acoustic interactions in a mouthpiece, and it has been known that a small geometrical change may affect the sound quality. In this study, we investigate the effects of mouthpiece geometry on the flow and sound generation in a single-reed instrument by conducting numerical flow simulations...

Porous media using short copper micro/nanofibers were created and their wicking characteristics of permeability K, capillary performance K/reff, effective pore radius reff, and porosity and drying characteristics were evaluated for loop heat pipe (LHP) applications. Different measurement methods were employed to evaluate the characteristics, and th...

For a small axial fan in a duct, the effects of acoustic resonance occurring in the duct on the flow around the fan are focused on. To clarify the condition for the intense acoustic resonance, the effects of the rotational speed and duct width on the flow and acoustic fields around the fan were investigated by compressible flow simulations with a v...

Computations of coupled phenomena between the fluid and acoustic interactions in the cavity flow and heat conduction in the flat plates (stack) installed in the cavity were performed to investigate the flow conditions for an effective thermoacoustic heat pump driven by acoustic radiation in cavity flows. This research presents the first computation...

For a small axial-flow fan installed in a duct, the effects of the acoustic resonance occurring in the duct on the flow field and aerodynamic characteristic were investigated. The measurements of the sound pressure level around the fan installed in two ducts with different widths showed that more intense acoustic resonance occurs for the narrower d...

The sound generation mechanisms of vocal folds’ self-induced oscillations have been investigated using vocal fold replicas. In this study, a compressible flow simulation coupled with a one-dimensional beam equation was conducted to study a reed-type artificial vocal fold. The vibrating reed was expressed by the volume penalization method in the aer...

A fluid-structure-acoustic interaction simulation of the reed-type artificial vocal fold was conducted to clarify the sound generation mechanisms with the reed vibration and turbulent flow in a cylindrical vocal tract. The vibrating reed was expressed by the volume penalization method in the aeroacoustic fields, and reed motion was predicted by a o...

Rotor behavior may affect the torque characteristics of gerotor pumps, but the measurement of the behavior has received little attention. Thus, in this study, we measure the rotor behavior of a gerotor pump used for automatic transmissions under various operating conditions. The experiments revealed that the inner rotor rotated near the middle of t...

The aerodynamic noise generated from bogie sections is one of the main sources of noise when high-speed trains run above 300 km/h. A new wind tunnel test method is proposed herein to determine the sound source distribution in detail and clarify the generation mechanism of the aerodynamic bogie noise in railways. Our wind tunnel test conducted for t...

No PDF available ABSTRACT The sound of a single-reed instrument is produced by the interactions among flow, reed oscillation, and acoustic resonance in the resonator. To investigate the effects of lip stiffness on the reed oscillation and acoustic propagation in the single-reed instrument, we conduct a flow simulation coupled with a dynamic beam an...

A numerical simulation of a single-reed instrument with a pressure chamber is conducted to examine the interaction among the flow, reed oscillation, and acoustic propagation. The flow and acoustic fields are predicted using the three-dimensional compressible Navier-Stokes equations, whereas the one-dimensional dynamic beam equation is solved for re...

For an isolated flute head joint, the effects of jet angle on harmonic structure of a single note are investigated within the practical range for human players. The mechanisms of these effects are discussed on the basis of both the radiated sound and the flow field measured with a hot-wire anemometer. The blowing parameters, viz., jet angle (angle...

Computations of coupled phenomena between the fluid–acoustic interactions in the cavity flow and heat conduction in a cascade of flat plates, which is called stack, installed in the cavity were performed to investigate the flow conditions for an effective thermoacoustic heat pump driven by acoustic radiation in cavity flows. The effects of stack po...

Our purpose is to clarify the effective control method with a plasma actuator to reduce the energy loss in the acoustic oscillatory flow in a curved duct. This flow appears in machinery related with sound such as speakers and thermoacoustic devices. In this study, simulations based on the compressible Navier-Stokes equations were conducted to clari...

In a cavity flow with acoustic radiation, self-sustained oscillations are controlled by a continuously or intermittently driven plasma actuator with elongated electrodes in the streamwise direction, which induces spanwise non-uniformity of the incoming boundary layer. To evaluate the control effects, wind tunnel experiments and compressible flow si...

The effects of the traveling sound wave generated by the speaker on diffusion flame were investigated experimentally. The sound frequency was varied from 50 to 1000 Hz using two sizes of loudspeakers, whose peak frequency showing the maximum sound pressure amplitude is nearly identical. A spirit lamp was used as the reference (diffusion) flame. Hav...

To establish the methodologies for utilization of oscillation energy in a cavity flow, the self-sustained oscillations in a flow over a cavity with and without a flexible beam are investigated, where stainless steel and aluminium beams are utilized. The coupled simulations for aeroacoustic phenomena and bending vibration of the beam are conducted a...

Direct aeroacoustic simulations of flow and sound around an instrument with an oscillating reed were performed on the basis of compressible Navier–Stokes equations along with experiments with an artificial blowing device. The measured reed displacement was utilized as forced vibration in the computations. The predicted sound pressure spectrum shows...

Small axial fans are used for cooling electronic equipment and are often installed in a casing with various slits. Direct aeroacoustic simulations and experiments were performed with different casing opening ratios to clarify the effects of the flow through the casing slits on the flow field and acoustic radiation around a small axial fan. Both the...

Gear behaviors affect the torque characteristics of an internal gear pump but have hardly been measured yet. This study measures the gear behaviors of an internal gear pump used for automatic transmission under various operating conditions. The inner gear rotates near the middle of the cover wall and casing side wall is not perpendicular to the dri...

The self-sustained oscillations in a cavity flow with acoustic radiation are controlled by an intermittently driven plasma actuator, which induces spanwise non-uniformity of the incoming boundary layer. To evaluate the control effects, compressible flow simulations have been conducted along with wind tunnel experiments. The feedback control by driv...

Small axial fans are used for cooling electronic devices, and have been often installed in a casing with slits to improve aerodynamic performance in recent years. However, when the fan is actually installed in a product, the inflow region may be limited to narrow space due to other components of the product. In order to clarify the effects of the u...

Aerodynamic noise generated from the bogie section is one of main sources when high speed trains run above 300km/h. Therefore, it is important to reduce the aerodynamic bogie noise appropriately. In this paper, the relationship between the flow field around the bogie and the aerodynamic bogie noise are investigated. To examine the relationship, a w...

The most suitable method for aeroacoustics simulation is the direct method based on the compressible Naver-Storkes Equation. However, it is required a large amount of computational resources. The decomposition method of the aerodynamic noise simulation can be solved problems of complex geometry such as automobiles with less computational resources....

To elucidate the selection mechanism of a predominant mode in acoustic radiation from the recorder, the jet oscillations predicted by direct aeroacoustic simulations are analyzed based on a proposed formula for hydrodynamic and acoustic jet displacements. The displacements are well represented by the formula, taking into account the non-zero initia...

In order to evaluate the interior noise caused by the flow around automobiles, it is necessary to clarify the nature of the pressure fluctuations on the surface of vehicle body. The pressure fluctuations around the vehicle which are caused by the fluid motion can be solved by unsteady-compressible Navier-Stokes equation. However, the differences be...

Featured Application Micro air vehicles. Abstract During insect flight, a feathering motion of the wing’s controls vortex shedding for lift enhancement. In this study, in order to control the flow around a wing flapping with simplified sinusoidal motion, plasma actuators were introduced to simplify the complex feathering motion. In a wind tunnel,...

It is important to understand the liquid-vapor phase interface shape developed by vapor generation on the porous body for the performance prediction of the loop heat pipe. A visualization experiment device, in which a porous body is immersed in the working liquid and its top surface is in contact with a viewing windows with a pore, was constructed...

The vapor-liquid interface behavior in the loop-heat-pipe (LHP) capillary evaporator is related to the thermal performance, but has not been sufficiently investigated. In this study, a visualization evaporator close to a practical environment is constructed using a sapphire tube, and the vapor-liquid interface behavior at the contact surface betwee...

Aerodynamic noise generated from the bogie section is one of main sources when high speed trains run above 300km/h. Therefore, it is important to reduce the aerodynamic bogie noise appropriately. In this paper, the countermeasures to control the noise are investigated. In order to examine the effect of the countermeasures on the aerodynamic noise,...

In order to clarify the effects of freestream turbulence on blade performance, wind tunnel experiments by using turbulence grids, fractal grids and an active turbulence generators were conducted. The results showed that it is possible to investigate the flow field around airfoil is placed in a strong turbulence field with the inertial sub range in...

In order to study the mechanism of the vehicle interior noise induced by the flow around the automobile, the near sound field around the rearview mirrors and the A-pillars is usually focused. As the difference in scale and intensity, in the near sound field, the pressure fluctuations related to the hydrodynamics and the acoustics can be considered...

In order to decompose hydrodynamic pressure fluctuations (HPF) and acoustic pressure fluctuations (APF) around the automobiles, a MESM microphone array and internal model for wind tunnel experiments were developed. A small array can be created by using a MEMS microphone. As a result, pressure fluctuation around an automobile can be divided into HPF...

In order to investigate effects of free stream turbulence on the aerodynamic performance of the NACA0012 at the Reynolds number 1.48×10⁵, a numerical analysis was performed with a turbulence grids installed upstream of the airfoil. Since the simulation domain has sufficient resolution to reproduce the grid turbulence upstream of the airfoil, it is...

To clarify the effects of jet angle on the radiated sound from the flute, the radiated sound and jet fluctuations were experimentally investigated. An artificial blowing device with an artificial oral cavity was used to change the jet angle and the geometric edge offset (the relative height of edge from the jet oscillation center) independently. Th...

A small axial-flow fan utilized in cooling systems of electronic equipment is often installed in a casing with slit structures. However, in some installation conditions, the ventilation through the slits is prevented due to obstructions. In this study, the effects of slit structures of the casing on performance and aerodynamic sound were investigat...

To clarify the effects of the windway geometry on the aeroacoustic feedback in the jet fluctuations in recorders, direct aeroacoustic simulations were performed along with experiments. The simulations were based on the compressible Navier-Stokes equations to predict the fluid-acoustic interactions. The volume penalization method was used to reprodu...

At specific velocities, intense tonal sound can be radiated from the flow around cascaded flat plates. This sound arises from the coupled phenomena of vortex shedding and acoustic resonance. To suppress such noise, we actively control the vortex shedding and acoustic radiation by oscillating the edges of every second plate in the cascade. The objec...

To clarify the effects of the windway geometry on the aeroacoustic feedback in the jet fluctuations in recorders, direct aeroacoustic simulations were performed along with experiments. The simulations were based on the compressible Navier-Stokes equations to predict the fluid-acoustic interactions. The volume penalization method was used to reprodu...

To clarify the effects of air jet conditions controlled by flutists on acoustic radiation, experiments were performed by an artificial blowing device with an artificial oral cavity. The experimental parameters are the flow rate, the jet angle between the jet issuing from the cavity exit and the surface of the mouth hole, the jet offset to the edge...

To mitigate the tonal noise from air flow around a cascade of flat plates, such as the grills in front of automobile engines, the thickness ratio of neighboring plates was varied in numerical simulations. Direct aeroacoustic simulations were based on compressible Navier–Stokes equations. For the baseline case with all plates at the thickness ratio...

Aerodynamic noise generated around a step such as front pillars of automobiles, which is transmitted into the cabin through the window glass, can negatively affect the comfort of the passengers. For the reduction of this noise, it is necessary to clarify the acoustic source and process of the propagation of the acoustic waves from the step. To do t...

Intense sound is radiated due to aeroacoustic feedback loop from a flow around the trailing edge of a curved plate with a kink shape such as a bonnet of an automobile. For the reduction of this noise, the control by a plasma actuator (PA) was investigated. The aim of this investigation is to clarify the effects of flow control by the PA on noise re...

In order to investigate the interior noise of automobiles, a cabin model for wind tunnel experiments and a MEMS microphone array were developed. Also we attempted to measure wavenumber-frequency spectrum of pressure fluctuations in the turbulent boundary layer to decompose hydro and acoustic pressure. The transfer function of the exterior aerodynam...

Development of micro air vehicles (MAV) has been progressed along with understanding of the flight mechanism of insects. In insect flight, it is well known to control the vortex shedding from flapping wings with feathering motions is important. In order to control flow around flapping wings with simplified sinusoidal motion, plasma actuators (PA) w...

Featured Application Noise reduction in high-speed transport vehicles. Abstract A plasma actuator comprising a dielectric layer sandwiched between upper and lower electrodes can induce a flow from the upper to lower electrode by means of an externally-applied electric field. Our objective is to clarify the mechanism by which such actuators can con...

At specific velocities, intense noise can be generated by the flow around a cascade of flat plates due to acoustic resonance. To reduce the aerodynamic noise, dielectric barrier discharge (DBD) plasma actuators (PAs) were utilized. The aim of this investigation was to clarify the control effects and the mechanism of noise reduction. To do this, win...

The objective of this investigation is to clarify reduction mechanism of cavity tone by using blowing jets in the incoming boundary layer and effects of spacing of the jets on noise reduction. To achieve this objective, direct aeroacoustic simulations based on the three-dimensional compressible Navier-Stokes equations were conducted with the variou...

In offshore wind farms, deterioration in power generation performance due to the mutual interference of flow around the wind turbines is a serious issue. To clarify the effects of wake-turbine blade interactions on the performance of wind farms, we conducted large-scale simulations of the flow around two full-scale wind turbines in a tandem-arrange...

To clarify the unsteady pressure distributions on the rotor blades of an axial fan, a pressure-sensitive paint (PSP) technique was used. To capture the image of the rotating fan as a static image, an optical derotator method with a dove prism was adopted. It was confirmed by preliminary experiments with a resonator and a speaker that the pressure f...

Flow and acoustic fields around a circular cylinder and a cascade of flat plates are clarified by direct simulations with a volume penalization method, which is a useful method to predict flow and acoustic fields around a complex geometry in a flow. The predicted results are compared with our experimental results or those of literatures. It is also...

To identify dominant acoustic sources in flows around a two-dimensional square cylinder in a uniform flow for the freestream Mach number from 0.2 to 0.6, the contributions of each term in acoustic sources in the Curle's and Lighthill's equations on the acoustic field are investigated. The acoustic fields are predicted by the direct simulations, and...

About 60% of primary energy is treated as waste heat but the temperature of this heat is low (200-300 0 C). Thermoacoustic engine convert heat energy into high amplitude sound waves, which is used to drive thermoacoustic refrigerator or pulse tube cryocoolers by replacing the mechanical piston such as compressors. The potential of thermoacoustic en...

Direct aeroacoustic simulations and experiments were performed regarding the flow and acoustic fields around a recorder, which is one of air-reed instruments. The present simulations reproduced the jet oscillations and acoustic radiation around the recorder with tone holes. The effects of conditions of the tone holes and the jet velocity on the flo...

In order to clarify the effects of the behaviors of the bubbles of aeration on the productivity of biomass, experiments including cultivation and computation were performed utilizing a bioreactor with a Taylor vortex flow in the annular gap of concentric cylinders. The shape of the inner cylinder and the position of the aeration were changed to var...

In musical instruments, the mode change of radiating sound is related with their quality. To clarify the flow and acoustic fields related with this mode change, we performed direct aeroacoustic simulations of flow and acoustic fields around two actual recorders with different shapes of windway. The computations are based on the compressible Navier-...

Suppression of cavity tone is one of the most important issues for the development of the high speed transportations. There have been many attempts to reduce the cavity tone by using plasma actuators, synthetic jet and piezo actuators. According to these investigations, brake up and three dimensional deformations of the large scale vorticities are...

To clarify the effects of freestream turbulence on cavity tones, flow and acoustic fields were directly predicted for cavity flows with various intensities of freestream turbulence. The freestream Mach number was 0.09 and the Reynolds number based on the cavity length was 4.0 × 10 ⁴ . The depth-to-length ratio of the cavity, D/L , was 0.5 and 2.5,...

Effect of oscillation of a plate in the flow and acoustic fields around a single flat plate and a cascade of flat plates are clarified by direct aeroacoustic simulations with volume penalization. This volume penalization method is one of useful methods to predict flow and acoustic fields around a complex geometry and moving object, where the penali...

The aim of this investigation is to clarify the effectiveness of aerodynamic noise control with the dielectric barrier discharge (DBD) plasma actuator (PA) over the cavity. The sound and velocity fields of flow around cavity were measured with a low noise wind tunnel. The depth-to-length ratio of the cavity was D/L = 0.5 and 2.5. The flow around th...

Flow and acoustic fields for cavity flows were directly simulated for various intensities of freestream turbulence to clarify what effects freestream turbulence had on cavity tones. The depth-to-length ratio of the cavity, D/L, was 0.5 and 2.5. The incoming boundary layer was laminar. Acoustic resonance in the direction of the cavity depth occurred...

This work presents an experimental investigation for effects of the spanwise spacing of small-jets placed in the approaching boundary layer on cavity tone. The sound and velocity fields of a flow around a cavity were measured with a low noise wind tunnel. The freestream velocity was changed from U0 = 10 - 45 m/s. The depth-to-length ratio of the ca...

The control of flow and aerodynamic noise around an automobile bonnet model with dielectric barrier discharged (DBD) plasma actuator (PA) was investigated, where the bonnet model consists of a curvilinear body with a kink shape. From a flow around this model, intense tonal noise radiates by fluid-acoustic interaction. The sound and velocity fields...

In order to solve aerodynamic sound radiated from the rotating bodies, including the acoustic interference of a moving object, we attempted to develop the time domain method for acoustic simulation based on a linearized Euler equation. Since pressure fluctuations of the sound wave are smaller than hydrodynamic pressure fluctuations, higher order si...

To clarify the mechanism of the control of cavity tone by plasma actuators of which electrodes are aligned with the oncoming flow, direct aeroacoustic simulations were performed along with wind tunnel experiments. The effects of the pitch of the actuators are focused on. The measured results show the most intense reduction of cavity tone is attaine...

Aerodynamic noise radiated from flat plate cascades are known to generate a strong sound pressure by the coupling of the flow field and the sound field. Although a cascade plates noise is dependent on the ratio of the plate thickness b and the flat plate spacing s, unfortunately, the ratio of the front grille of the conventional vehicles are close...

This work presents an experimental investigation for effects of the spanwise spacing of small-jets placed in the approaching boundary layer on cavity tone. The sound and velocity fields of a flow around a cavity were measured with a low noise wind tunnel. The freestream velocity was changed from U_0 = 10-45 m/s. The depth-to-length ratio of the cav...

The aim of this investigation is to clarify the relationship between the variation of large-scale eddies by jets in the upstream boundary layer and the reduction of cavity tone. Direct simulations of flow and acoustic fields for cavity flow were performed with installation of jets with various intervals d_j and inclination angles θ. The depth-to-le...

To clarify fluid-acoustic interactions in an actual recorder with opened and closed tone holes, flow and acoustic fields were directly numerically simulated on the basis of the compressible Navier-Stokes equations. To validate the simulation accuracy, the flow field around the windway and sound pressure above the window were measured. The predicted...

Intense tonal sound radiates from flows around a trailing edge with an upstream kink shape such as found in an automotive body. To clarify the acoustic radiation mechanism and the effects of the kink shape angle on tonal sound, direct numerical simulations (DNS) of flows and sound fields and wind tunnel experiments were performed. As a result, the...

In order to make a strong turbulence field in a wind tunnel, the properties of 3-D multi-scale turbulence grid using fractal was experimentally investigated. The intensity and scale of turbulence generated by the developed multi-scale turbulence grid were larger than that of the conventional grid turbulence. On the other hand, the turbulence Reynol...

In order to clarify the effects of the distance between the plates on aerodynamic sound and flows around a cascade of flat plates, wind tunnel experiments were performed with the various ratios of the distance between the plates to thickness, s/b = 0.5, 1.0, 1.5, 3.0, 6.0 and 13.0. For s/b = 6.0 and 3.0, the intense aerodynamic sound with acoustic...

The aim of this investigation is to clarify the effectiveness of aerodynamic noise control with a dielectric barrier discharge (DBD) plasma actuator (PA) over the cavity. The sound and velocity fields of a flow around a cavity were measured with a low noise wind tunnel. The experiments were carried out at the freestream velocity of 10-45 m/s. The d...

The aim of this investigation is to clarify the effect of aerodynamic noise control of the cascade of flat plates with a dielectric barrier discharge (DBD) plasma actuator (PA). The sound and velocity fields of a flow around a cascade of flat plates were measured with a low noise wind tunnel. The experiments were carried out at the flow velocity fr...

In order to clarify the generation mechanism of aerodynamic noise from axial flow fans, unsteady pressure fluctuation on the surface of blades were measured by time resolved Pressure Sensitive Paint based on micro-material slurry (MS-PSP). The frequency resolution of the developed PSP is up to 300Hz and the sensitivity is almost the same as the con...