A non-intrusive and continuous separation technique for suspended particles in a microchannel has been developed by utilizing acoustic radiation force with two ultrasonic transducers. The technique has two major advantages that the acoustic radiation force acts on particles in proportion to particle diameter, and collects particles to the nodal positions of the standing wave field perpendicular to the flow direction. Thus the large size particles have shorter time of transfer to the nodal positions than the small size particles. Particle velocities toward the nodal position within the sound field were measured by particle tracking velocimetry, and both the migration times of particle transfer to the nodal positions and the acoustic radiation force were evaluated from the particle images and velocity data in order to separate particles in the flow field. The ultrasonic transducers with 5 and 2.5 MHz were equipped parallel to the flow direction. Both large and small particles in the aqueous solution were trapped at the nodes of the upstream in 5 MHz sound field, and 2.5 MHz transducer was radiated to move only large particles toward a nodal position of its sound field. The exposure time of 2.5 MHz transducer was determined from the migration times of large and small particles transfer to the nodal positions. It is confirmed that the continuous and selective separation based on particle diameter was accomplished by the present technique.
The lattice kinetic scheme (LKS) for a binary miscible fluid mixture was applied to the simulation of the mass transfer of calcium in concrete. Cement paste, a major component of concrete, is a porous medium with a complicated three-dimensional geometry. The structure of the model concrete was selected on the basis of experimental data obtained by high-intensity X-ray computed tomography. The LKS, an improved version of the original lattice Boltzmann method, was used to save computational memory and to maintain numerical stability. First, an unsteady convection-diffusion problem was examined, and the accuracy of the method and the error norms with various lattice resolutions were investigated. Next, the problem of the calcium current in concrete was simulated. Pressure drops in the concrete were calculated for various Reynolds numbers, and the results were compared with those of an empirical equation based on experimental data. Also, velocity fields and concentration profiles were obtained at a pore scale for a structure with inhomogeneous mass diffusivities. These simulations showed that the present method might be useful for predicting calcium leaching in concrete from the microscopic point of view.
Acoustic Inkjet Printing uses an acoustic beam focused on a free liquid surface for drop ejection. This method can eject small drops without precise nozzle fabrication in comparison with thermal inkjet and piezoelectric inkjet. The fresnel lens was selected for focusing acoustic waves because of the precise and easy manufacturing by LSI process. The actual devise was made from a Si substrate and characteristics of its drop ejection were investigated. Furthermore, sound field by fresnel lens was calculated using Rayleigh's Equation to be compared with the experimental results that showed good agreement. Finally it was proved that acoustic inkjet printing with fresnel lens is suitable for drop modulation by utilizing second harmonic focus.
The relationships between large-scale bulge and valley structures and bursting events in a zero-pressure-gradient turbulent boundary layer (TBL) are investigated by means of laboratory experiments carried out in a wind tunnel. To investigate the spatiotemporal structures of coherent motions in a TBL, multipoint instantaneous streamwise velocities and instantaneous wall static pressures are simultaneously measured using a combination of a rake of 23 I-type hot-wire probes, which covers entire TBL, and a microphone pressure sensor. The KL (Karhunen-Loève) expansion is applied to the measured velocity signals. The flow field is reconstructed by using lower- or higher-order modes to investigate the coherent motions in the TBL. The bursting events are detected by applying the VITA (Variable Interval Time Average) technique to the instantaneous velocity signals in the original flow. The bulge and valley structures are detected by using the newly proposed conditional sampling method, which is applied to both the original flow and the reconstructed flow by using the KL expansion. The results show that at lower modes, only the large-scale motions rotating against the mean shear stress accompany the bursting events. At higher modes, however, the large-scale motions are found to be poorly related to the bursting events.
In order to get accurate measurements of air entrainment in a suction sump, we design a new and simple conductance-type electric bubble sensor, which can detect the existence of air bubbles inside a suction pipe with no disturbances by the sensor probe and with a fine spatial resolution. We focus on occurrence-time ratio γ of the air entrainment, and compare the result by the present sensor with those by conventional two methods; namely, visual and auditory ones. As a result, we show the criteria which specify lower-accuracy conditions in the conventional methods. By the visual method, the accuracy of γ becomes low, when γ is less than 0.05. By the auditory method, the accuracy of γ becomes low, when submergence depth S of the suction pipe is close to the critical one Sc.
A new miniaturized fiber-optic laser Doppler velocimetry (LDV) sensor has been developed, which is capable of measuring the local velocity in various semi-opaque and opaque fluid flows, particularly whole blood velocity in vessels. The sensor has a convex lens-like fiber tip as a pickup and an improved optical transmission system with markedly decreased stray light. This paper describes methods for fabricating fiber tips like concave and convex lens and the characteristics of the optical sensor system equipped with the fabricated fiber tip. Conventional fiber-optic LDV sensors developed up to now have not been capable of measuring such opaque fluids because scattered light from scattering particles as erythrocytes has very low intensity, which makes signal-to-noise ratio of Doppler signal received by a sensor pickup significantly decreased. To overcome these problems, convex lens-like fiber tips have been fabricated by chemical etching, in which quartz fibers of multimode graded refractive index have been etched in aqueous solutions of hydrogen fluoride and ammonium fluoride under the appropriately controlled condition of the concentration of the solution, the etching duration time and the etchant temperature to obtain the desired curvature radius of the lens-like surface of the fiber tip. In this fiber-optic sensor, a laser beam emitted from the fiber tip can be focused at any position from about 0.1 to 0.5 mm distant from the fiber tip according to its curvature radius. The convex lens-like etched tip totally reduced the intensity of undesired reflecting light at the fiber end by 1/2 to 1/6 compared with normal cut fiber tip. Consequently, this fiber-optic LDV sensor system is capable of measuring the local flow velocity in semi-opaque and opaque fluids, whose turbidity was about five times higher than by any kinds of previous sensors.
One of the useful ways to measure the effect of the flow control devise is to use the wall-shear stress sensor to measure the wall-shear stress directly. The sensor used in this paper measures the wall-shear stress, which is reduced by the flow control devise. In this paper, the wall-shear stress of the plane shear layer with the plasma synthetic jet actuator (PSJA) is investigated. PSJA is a flow control device composed of electrodes with A.C. signal. The actuator uses electrohydrodynamic (EHD) effect and induces flow around the electrodes. PSJA has great advantage such as miniaturization, maintenance free, and easy to control compared to other actuators. In this paper, the wall-shear stress of plane shear layer in a low-speed turbulent wind tunnel is observed to measure the effect of the PSJA. The results show that the PSJA changes the flow condition of shear layer by accelerating the flow in shear layer. The wall-shear stress reduces and increases according to the displacement of the wall-shear stress sensor and the actuator.
The fluctuating flow phenomena on a two-phase flow through a vertical sudden expansion pipe system are investigated experimentally and visually. The effect of the volumetric gas flow rate ratio within the range of bubbly flow is investigated. Simple flow control methods are proposed and tested in comparison with the normal expansion case. The first method applies control by mounting a ring shaped obstacle downstream the expansion, and the second by mounting a step-ring just downstream. These two methods are based on a different control concept. The first is based on splitting the vortex region, thus decreasing its intensity, and the second on decreasing the overall generated vortex region length. In single-phase flow, only one dominant frequency is observed. However, when gas is induced, two dominant peaks appear and a tendency of the second peak to shift to lower frequency values when increasing the volumetric gas fraction is observed. When the flow control methods are applied, the fluctuation frequency is not affected, but the fluctuation amplitude decreases. From pressure distribution measurements under several flow conditions, it was confirmed that when the flow control methods are applied, drag reduction is achieved as well.
We manufactured a new hot-wire probe with two parallel wires placed closely together for measuring a transitional boundary-layer flow. The main feature of this new probe is that it is much smaller than a conventional multi-sensor probe, such as an X-type probe. Thus, the new probe can be regarded as a sensor similar in configuration to a single normal probe and is expected to provide high spatial resolution for fluctuating velocities in a transitional boundary layer. The measurement principle is very simple, as the streamwise and the normalwise velocity components are simultaneously obtained from the sums and the differences of the linearized outputs of two hot-wire circuits with the aid of the look-up-matrix method. It was found that the complicated relations between the hot-wire-circuit outputs and the flow angle can be simplified by limiting the flow angle to within θ = ±30 deg. The new hot-wire probe was used to measure the velocity profiles in a low Reynolds number turbulent boundary layer. The results revealed that the probe is a useful tool for measuring velocities in a transitional boundary layer having a thickness of only several mm.
Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, the time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of the vortex is evident from both velocity and pressure measurements: The power spectral density (PSD) of the transverse velocity fluctuation increases in the lower frequency range, and the distribution of the pressure fluctuation exhibits an elongated shape in the z direction as well as two peaks slightly off from the vortex center. The distribution of the measured velocity-pressure correlation varies significantly near the center of the vortex especially in downstream locations.
The lattice Boltzmann method (LBM) is applied to simulation of fluid flows in anisotropic porous media with the Brinkman equation. The Brinkman equation is recovered from a kinetic equation for the distribution function that has a forcing term to introduce anisotropy of the permeability of the porous media. Since the forcing term contains the drag force proportional to the fluid velocity, the LBM needs matrix calculation to obtain the fluid velocity through the definition of the momentum. The velocity profiles of the LBM show good agreement with analytical solutions for the Poiseuille flow and for the Couette flow filled with anisotropic porous media. The contour lines of the stream functions obtained by the LBM show good agreement with those of the finite difference method (FDM) in the numerical simulation of a lid-driven cavity flow for different fundamental parameters, e.g., Darcy number, inclination of the principal permeability direction, and permeability ratio. By increasing grid size, the LBM is able to decrease the compressibility effect, and reduces the deviation of the maximum values of the stream function between the LBM and the FDM. On the same grid size, the LBM takes less time than the conventional FDM to get the steady solutions. This paper leads to the conclusion that the LBM can simulate incompressible flow in anisotropic porous media at the representative elementary volume scale.
Globe valves are one of the oldest valve types used for throttling applications for all sizes due to better controllability and range. One of the major limitations associated with the use of globe valves in liquid application is cavitation. It takes place both in part open and in fully open conditions due to varied reasons. There are different designs of globe valves available but for control valve applications, cage and plug designs are widely employed. Cage and plug design consists of body, valve cage, plug and an actuating mechanism. Actuating mechanism is connected to the valve plug (moving part), through valve shaft. There are many investigations reported about the flow visualization and numerical simulation of normal type globe valves. But study on valves with cage and plug design are not tried in detail. The objective of the present work is to provide a comprehensive study of flow through a globe valve with cage and plug design with emphasis on cavitation. Cavitation reduction is achieved by breaking the flow in the form of more than one liquid jets, there by increasing the turbulence in the valve flow path. This ensures the local static pressure not going below vapour pressure. Experimental studies were done in the water test facility with an operating pressure of 1.6 MPa and flow rate of 0.05 m3/s. In the study, total area of opening of the valve and the valve stroke were kept constant.
The near-field flow structure of an intense streamwise vortex filament encountering normally with a blade tip vortex was investigated experimentally. Three cases were investigated, direct impingement, interactions on the pressure side and interactions over the suctions side. The effects of blade-vortex interaction were found to be strongly dependent on whether the vortex filament passed over the pressure or suction side of the blade. In case of, zero vortex-blade tip separation (direct impingement), the peak tangential velocity and total circulation of the interaction vortex remained basically unchanged, regardless of downstream distance, but had values larger than the generator vortex, while the core circulation and the core radius increased almost linearly with downstream distance, similar to an undisturbed generator vortex. The maximum total turbulent energy decreased as x/c increased. In summary, the present experiment deals with the normal interactions of streamwise vortex with another tip vortex shed by a blade end-tip, and focuses on the resultant vortex structures and peak values due to the interaction itself.
Experimental investigations were conducted to study the effect of micro-bubbles injected into water flowing through straight and helical pipes with different curvature ( 0.025, 0.05 and 0.1). The micro-bubbles were produced using two hydrocyclone micro-bubble generators positioned face to face with opposite direction of swirl flow. The mean diameter of the micro-bubbles generated was about 60μ m, while the maximum diameter observed was 174μ m, with air fraction, which will be defined in Eq.(4), ranging from 0.21% to 0.44%. The effect of the Reynolds number on the drag reduction is also presented. The experimental results show that, the micro-bubble has an effect of drag reduction on both straight and helical pipes, though the drag reduction in a straight pipe is much higher than that in a helical pipe, because of the secondary flow in a helical pipe. It is found that the drag reduction increases with the decrease of curvature and the increase of air fraction. The maximum value of drag reduction ratio was 51% in case of a straight pipe, while that for a helical pipe was 16%.
In this study, we deal with the tumbling, which is a rotating motion with the axis perpendicular to the falling direction. Our purpose is to reveal the fundamental aerodynamic characteristics of the tumbling, experimentally. Regarding a test plate, we consider a prism with a rectangular cross section with a depth-to-width ratio λ of 0.3. The results are as follows. The reduced terminal rotating rate Ω*, the lift coefficient CL, the drag coefficient CD and the lift-to-drag ratio CL/CD are independent of the aspect ratio AR, when AR is greater than 10. As the inertia moment ratio I* increases from zero to 50, Ω*, CL and CD increase. However, Ω*, CL and CD become almost constant, at I* greater than 50. We propose the empirical formulae to predict them. At low I*, the tumbling shows a dominant periodicity of 360 deg.
The Turbulent channel flow over a backward-facing step was investigated experimentally by using suction through a slit at the bottom corner of the step. Suction was continuously applied, and the direction of the suction was perpendicular and horizontal to the main flow. The suction flow ratio was varied from 0.00 to 0.15. The wall static pressure and local heat transfer coefficient were measured behind the backward-facing step. The velocity profiles and turbulent quantities were measured by PIV. It was found that the pressure drop at the step was reduced and the heat transfer coefficient in the recirculating region was improved by suction. The suction direction did not affect the heat transfer or fluid flow characteristics. Enhancement of the heat transfer coefficient was related to the increase in turbulent energy, Reynolds shear stress and turbulent diffusions. However, the region where these quantities increase was limited to the area immediately behind the step. When strong suction was applied, periodic fluctuating motion occurred.
The counter-rotating axial flow fan shows that the complex flow characteristics with three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in counter-rotating axial flow fan, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. The purpose of this study is, therefore, to present the periodic characteristics of the blade passage flow, the wake and the tip vortex, which are utilized for the blade design data for the improvement of the aerodynamic characteristics, the reduction of the aerodynamic noise level and vibration characteristics of the counter-rotating axial flow fan. In this paper, the three-dimensional unsteady flow by the rotor-rotor interaction of the CRF were investigated at the design point(peak efficiency operating point). Unsteady flow fields in the CRF are measured at the cross-sectional planes of the upstream, between and downstream of each rotor using the 45° inclined hot-wire probe. The stationary hot-wire technique used the 45° inclined hot-wire probe, which rotates successively with 120 degrees increments about its own axis. And, the sampling data of unsteady flow fields were phase-locked averaged to remove the random components.
Ultrasonic cleaning device was modeled and the collapse of a single bubble in an ultrasonic pressure field was studied using a finite-volume 2D axisymmetrical model. The pressure field was generated with the bottom of a container oscillating at 33 kHz. Spherical air bubble of resonance size was induced into water near the bottom where it violently collapsed. Compressibility of both phases was taken into account and the interface between air and water was captured using Volume-Of-Fluid approach. Maximal pressures, temperatures and velocities, generated during the collapse, were studied with regard to the initial bubble distance from the bottom. The results were compared for different time step sizes and grid densities where some great differences were found. For validation of the model a separate numerical simulation was run for a bubble collapsing near a rigid wall in a uniform pressure field. The computed bubble shapes were compared to the experimentally observed bubble shapes of Philipp and Lauterborn (1998) and a very good agreement was found. Although the collapse of just one bubble was studied, the results obtained gave good insight into conditions that happen due to cavitation in a near-wall region of ultrasonic cleaning devices.
It was well-known that a disturbance, introduced artificially into a supercritical laminar boundary layer along a flat plate, is still laminar in the initial stage of its downstream development. Thus, we named it a "laminar spot" because it resembles a turbulent spot though its velocity perturbation remains laminar. From velocity measurements using a rake-type 16-channel hot-wire probe, we found that in the first stage of the downstream development of a laminar spot, its maximum width was at 0.2δ (what is called the critical layer) and one-half of its lateral growth angle was about 5°, which is almost one-half that of a turbulent spot. We call this region a "laminar spot region". In the present study, we measured in detail the velocity field of a laminar spot using a new hot-wire probe in the laminar spot region. The results showed that a laminar spot consists of some hairpin vortices and some induced U-shaped vortices under the hairpin vortices. Because of the interaction of the velocities induced by the respective vortex legs, the legs of the U-shaped vortices were located at the outermost part of the spot. Moreover, the new vortex legs extended spanwise at about 4° as the spot traveled downstream. Consequently, we concluded that the laminar spot grew spanwise in accordance with the span of these vortex legs.
Clinical arterial stiffness indexes such as PWV (pulse wave velocity) or PP (pulse pressure), which are obtained by analyzing blood pressure pulse waveforms in vivo, are used in the prognosis of cardiovascular diseases and thus analyses of pulse waveform are clinically important. The pulse wave in vivo, however, is complicated because of the complex viscoelastic property of the blood vessel wall. In addition, numerical flow simulations are useful for understanding pulse wave propagation in circulatory systems. Our proposed nonlinear one-dimensional numerical simulation model can accurately simulate the measurements of pressure waves in a silicone rubber tube and indicate that the viscoelasticity of the tube wall was significantly influenced by a single pulse waveform; however, the influence of viscoelasticity change on periodic pulsatile wave propagation has not yet been studied. The purpose of this study was therefore to investigate the effect of viscoelasticity change on the periodic pulsatile wave. For this purpose, we examined the effect of the viscoelasticity of a single silicone tube on periodic pulse wave propagation by comparing the calculated results using a one-dimensional model. As a result, the one-dimensional model could accurately express the experimental results with periodic pulsatile waves. In addition, both PWV and PP increase when the viscoelastic value of the dynamic modulus elasticity ratio increases, because increasing the elastic modulus is more effective than the energy dissipation effect by viscoelasticity change. Consequently, it is necessary to measure the viscoelastic property of the vessel wall accurately in order to estimate the arterial stiffness index (PWV and PP) accurately.
The purpose of this study is to search for a new method of dispersing spilled heavy oil, which has a detrimental effect on the natural environment and marine ecosystem. A method ejecting a waterjet vertically downward to heavy oil on the water surface was studied, particularly focusing on the effect of the guide nozzle shape. The waterjet comprised heavy oil and minute air bubbles, and passed through the hole of the guide nozzle. Thirteen guide nozzle shapes were tested and compared. The dispersion efficiency of a tapered hole was the best among the 13 nozzles. The flow in the hole of the guide nozzles was recorded by a high-speed video camera. The occurrence of two flows, regular and counter flows, was observed in the taper guide nozzle. It seemed that the counter flows generated the shearing force between the waterjet and the heavy oil layer. It is considered that the shearing force determines the surplus efficiency of disperse.