In this paper, it is clarified that the effect on annular supersonic jet by geometrical shape of annular nozzle which is applied in various fields in industry. An unsteady characteristics of annular supersonic jet issued from annular nozzle is given by the experiment. In particular, an effect of pressure vibration on flow filed is clarified. Moreover, the unsteady flow of the annular supersonic jet is calculated by the numerical analysis. And the effect on flow field by difference of nozzle exit shape and the static pressure in vortex region generated at nozzle exit are clarified. It was found that the nozzle shape and the stagnation pressure influenced the vortex region generated at nozzle exit, the separation point of flow and the pressure decrease in vortex region. When the annular nozzle is to be used as atomization nozzle, it is suggested that the pressure vibration of the nozzle exit and the static pressure of vortex region produce effects upon generation of metallic fine powder.

View full abstract

A supersonic jet is utilized in industries to cool a heated material, to blow the dust away from the product and so on, and also used as propulsion of space vehicle in aviation field. The jet is usually underexpanded or overexpanded, having a cell structure. When the jet impinges on materials having various geometries, the jet oscillates itself and a noise radiates from it. In this paper, the underexpanded jet impinges normally on a thin plate. Oscillation of the jet and vibration of the plate were analyzed at different nozzle-plate spacings. The flow fields on thin plates with various thicknesses were compared to each other. As a result, an effect of the flow pattern of the impinging jet was found on the vibration of the elastic plate.

View full abstract

In recent years, the ceramic electronic device is a key technology in the field of information, communication, and energy in which the innovation is intense. In this situation, spray coating of ceramic particle at room-temperature has been under development in Japan. The biggest advantage of the technology is that the ceramic particle is deposited at room temperature. Therefore, the ceramic coating can be used as various electric devices. However, the gasdynamic aspect of the spray technology is still unclear. This study investigates the effects of stagnation pressure, distance from the nozzle exit to substrate (SOD) and particle diameter on the impact velocity of the particle by numerical simulation. As a result, spray conditions that can be coat ceramic particle is clarified

View full abstract

The vortex ring generated by the open end shock tube is studied using shadowgraph and schlieren method. The shadowgraph image shows the vortex core, which shows a vortex ring formation. We examine the propagation process of the vortex ring for three shock numbers, 1.10, 1.21, and 1.31. The position which vortex ring is visualized is L/D=1.0, 3.0 ,5.0, where L is distance from open end to vortex ring , D is open end inner diameter. Vortex ring propagation process is observed, and vortex characteristics is discussed.

View full abstract

When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection (RR) and Mach reflection (MR) is affected by this phenomenon. Many papers have been described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.

View full abstract

Underexpanded jet impinging normally on a flat plate shows a complicated flow pattern where the recirculation zone can be present in front of the plate, oscillation of the stand-off shock is possible and so on. After impinging on the plate the jet spreads radially on it, resulting in the formation of a radially underexpanded wall jet. In order to make clear the structure of this wall jet, the collision of the flows from the opposing tubes is used. After the collision the radial jet forms. The Shadowgraph and Schlieren photography are used to visualize the flow field and the result are examined.

View full abstract

The present paper describes the effect of duct length on acoustic characteristics of over-expanded jet which are discharged from convergent-divergent nozzle. A duct made of annular metal was installed at the nozzle exit and varied in length from 0 and 6D. A Schlieren optical system is used to visualize detailed jet structures. Acoustic measurement is performed to obtain noise spectra. The results obtained show that the frequency of the acoustic tone due to the shock wave within the nozzle somewhat increases with an increase in the nozzle pressure ratio, and the acoustic tones take place in two stages. The duct devices suppress the acoustic tone and the screech tone.

View full abstract

In this paper, it was studied about boundary layer control of jet flow issuing from divergent nozzles. And it has aimed to clarify behavior about jet boundary layer and jet flow issuing from divergent nozzles. In the case to change divergent angle, changing of separation point and behavior of the flow was clarified by experiment and numerical analysis. Moreover, the frequency analysis of the pressure vibration of the flow field was studied by experiment, and the influence was clarified about jet boundary layer and self-included oscillation from the control of the separation point. As a result, it is clarified that the position of the separation point is different by the stagnation pressure, and the behavior of the jet flow of the downstream region and the flow of the boundary layer are affected by the separation of the flow.

View full abstract

It is well known that some of the noise sources of noise which radiate from an exhaust pipe of automobile engine exist in the flow field downstream of the pipe end. An unsteady jet issues periodically from the pipe end with shock wave, so that the discharged shock interacts with the jet, resulting in the formation of the complicated flow pattern. To clarify the mechanism of noise generation, the flow field downstream of the pipe end is experimentally examined using a shock tube. The shocks are successively discharged from open end of the pipe. The first shock induces the jet from the pipe end. And the following shock interacts with the jet. The flow field is visualized by shadowgraph method and different types of pressure waves are observed.

View full abstract

The objective of the present study is to investigate the transient flow through the ejector system. An attempt is made to investigate the interesting and conflicting phenomenon of the infinite entrainment of secondary stream into the primary stream from a finite secondary chamber. The present study is also intended to identify the operating range of vacuum ejector-diffuser systems where the steady flow assumption can be applied without uncertainty, with the help of a computational fluid dynamics method. The results obtained show that the one and only condition in which an infinite mass entrainment is possible in such types of ejectors is the generation of a re-circulation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium of pressures at this point. A steady flow assumption is valid only after this point.

View full abstract

It is said that starting characteristics of supersonic wind tunnel depend on the blockage ratio. However, analytical correlation for the blockage ratio generally disagree with experimental results. We performed wind tunnel tests and numerical simulations with flat plate and cylindrical models to investigate the effects of blockage ratio, model length, and 2nd throat area for JAXA 1m by lm Supersonic Wind Tunnel (SWT1). It was found that the starting limit depends on model length at some test conditions due to total pressure loss as well as blockage ratio. It was also shown importance of 2nd throat configurations in the blow down supersonic wind tunnel.

View full abstract

This paper describes an experimental study on the supersonic internal flows with Pseudo-Shock Waves (PSW) in a straight square duct with cross section of 80×80mm^2, using the pressure-vacuum type Mach 2 and Mach 4 supersonic wind tunnel of Muroran Institute of Technology. The formation process and characteristics of the Mach 2 and Mach 4 PSW were investigated by high speed digital camera observation and duct wall pressure fluctuation measurements. The free stream Mach number and unit Reynolds number just upstream of the PSW were M_∞=1.96, Re_∞=2.43×10^7m^<-1> and M_∞=3.98, Re_∞=2.22×10^7m^<-1>.

View full abstract

In the present paper, the experimental investigation is described to clarify the mixing characteristics in the supersonic flow of the flexible vortex generator (FVG). In the experiment, the time-averaged total pressure distributions were measured by DSA (Digital Sensor Array). Moreover, the unsteady pressure distributions were measured by a pressure sensor. The flow fields were visualized and recorded by using schlieren method and a high-speed camera respectively. Oscillation frequencies of the FVG were calculated based on schlieren images. Schlieren images and tome-averaged total pressure distribution indicated that the FVG oscillation caused the change of the shock wave structure. The unsteady pressure distributions indicated that the FVG produced large amplitude of pressure fluctuation. It can be concluded that the FVG was effective to churn the mainstream.

View full abstract

The effect of a rearward-facing step on plasma ignition in supersonic flow was experimentally and numerically investigated. The rearward-facing step was installed between a plasma jet injector and a fuel injector in order to enhance ignition and combustion. However, the installation of the step resulted in decrease in wall pressure increase due to combustion. Numerical simulation reveals that the fuel injected behind a rearward-facing step was diffused widely in the recirculation zone, but high temperature PJ plume hardly diffused in this recirculation zone. Therefore, the recirculation zone behind a rearward-facing step was not suitable for ignition and flameholding. These results were consistent with the trends in the ignition experiment.

View full abstract

The supersonic flow past a cavity induces large pressure oscillations that may create many undesirable effects in aerospace applications. The occurrence of oscillation in the cavity causes to increase aircraft noise and drag. For these reasons, the area of cavity flow has attracted the researchers for years. In spite of numerous research investigations, the understanding of the flow physics governing the behavior and the practical methods of suppressing cavity-induced pressure oscillations have not yet been studied adequately. In the present study, a new passive control technique has been investigated experimentally by modifying the front wall of a square cavity. The objective of the study is to determine the effectiveness of the proposed control devices as oscillation suppressors.

View full abstract

This paper describes an experimental study on the flow characteristics and control of a rectangular supersonic intake model for ramjet engines. The experiment was conducted using the Mach 2 vacuum type supersonic wind tunnel. The effects of variation of the cavity shape and cavity bleed on the internal flow characteristics of the intake are shown by the experimental results of flow visualization and total pressure distribution measurements in the transverse cross section.

View full abstract

An experimental study has been carried out to investigate an influence of the airfoil thickness on self-excited shock wave oscillation on a 2D symmetrical circular-arc airfoil in internal transonic flow. 12% and 10% thickness airfoils were tested newly. Shock wave positions were measured by using a line scan camera. The result shows that the shock wave oscillation phenomenon becomes unstable and the continuousness of the shock wave oscillation weakens as the thickness becomes small, and that the shock wave frequency overall lowers as the thickness becomes small, and rises as a shock wave average position gets closer to the trailing edge for the cases of both thicknesses.

View full abstract

The three-dimensional flow structure induced by normal shock-wave/boundary-layer interaction in a transonic diffuser is investigated by a laser-induced fluorescence (LIF) method. This diagnostic system uses an argon-ion laser as a light source, and target gas is dry nitrogen with iodine seeded as a fluorescence material. The Mach-number distributions in the diffuser are obtained from the measured fluorescence intensity, and the three-dimensional shape of the boundary layers is obtained immediately behind the shock wave. The oil-flow surface visualization is also done, and the vortex-like patterns appear in the interaction region. These flow characteristics are reproduced very well by solving the Navier-Stokes equations numerically, and it is found that the vortices are generated at the foot of the shock wave and bended downstream. The calculated result also reveals that the complicated wave configuration is formed at the diffuser corner. The simple flow model is constructed by considering this wave configuration. This model can explain very well the three-dimensional flow characteristics.

View full abstract

The two-stage High Velocity Oxy-Fuel (HVOF) thermal spray gun has a mixing chamber between a combustion chamber and a supersonic nozzle followed by a straight barrel. The combustion gas is discharged into the mixing chamber, then the gas temperature is lowered in the chamber by injecting nitrogen gas at room temperature. The lowered gas temperature is beneficial from the view point of less oxidation of the spray particle. In this paper, the characteristics of the gas in the mixture chamber are clarified by the comparison between the cold-flow experiment and theoretical calculation.

View full abstract

Laser-induced thermal acoustics was used to measure the temperature profiles induced behind spherical shock waves, generated by high-voltage discharge with an energy of 6 J, in air. Nd:YAG laser (wavelength: 532 nm, energy: 300 mJ, pulse duration: 10 ns, line width: 0.005 cm^<-1>) and Ar-ion laser (wavelength: 488 nm, power: 4 W) served as pump and probe lasers for the LITA measurements, respectively. The peak temperatures were in good agreement with results calculated with the Euler equation. The temperature profiles behind shock, however, differed in decay rates. The peak temperatures behind the shock wave were determined by reflected overpressure and agreed with those from LITA measurement within a maximum error of 5%.

View full abstract

When a compression wave generated by a train entering a tunnel is propagated through the tunnel and reaches the exit portal, a pressure pulse ('micro-pressure wave') is radiated from the exit portal. The distortion of the compression wave during propagation in a slab-track tunnel is important for estimating the magnitude of the micro-pressure wave radiated from the exit portal. In this paper, the dependence of the distortion of the compression wave on the initial waveform at the tunnel entrance is investigated theoretically and numerically.

View full abstract

It was carried out that exhaust noise generated by automobile engine is cause of shock waves. There is a limit to acoustic engineering to reduction exhaust noise. Therefore it is effective that to see exhaust noise as phenomenon related to shock waves. In this report, connect end of shock tube to two-dimensional models simulated automobile silencer. It was visualization by shadow graph to command shock wave propagation. In parallel measuring pressure in models.

View full abstract

Shock wave propagation and collapse of gas bubbles caused by a shock wave in liquid containing gas bubbles are of large interest in relation to characteristics of water hammer, blowdown of high pressure liquid, and cavitation bubble collapse. In this paper experimental studies on the collapse of air bubbles by a shock wave using a water shock tube and high speed photography are described. High speed schlieren photographs show the processes of high pressure region formation or shock wave formation near multiple air bubbles when the bubbles rebound.

View full abstract

To investigate a use for a shock wave driven by a pulsed-detonation system, shock waves discharged from a detonation tube were observed. We took several photographs of the shock waves by using a shadow-graph camera having high resolution of time, and an empirical formula of location of the shock wave propagating in the radial and axial directions of the detonation tube was obtained. In addition, a sound pressure level at 10 km from the detonation tube was estimated. It was calculated that the sound pressure level at 1 m from the open end of the detonation tube was 179 dB.

View full abstract

Flow structures around hypersonic TSTO launch vehicle were investigated by utilizing the electrical discharge method. First, boundary layers near the orbiter surface were observed by a visualization technique of boundary layers. Subsequently, lateral and cross-sectional shock shapes around TSTO launch vehicle were observed by a visualization technique of shock waves. From these results, it was confirmed that a separation shock wave was generated near the orbiter surface. In this study, the visualizations were carried out at Mach 10.

View full abstract

Numerical analyses are conducted on a nanosecond positive pulse dielectric barrier discharge-induced nonthermal plasma (NTP) for pollution control. In the numerical analysis, commercial simulation software, CFD-ACE+ solver, is used. In the one-dimensional simulation, a streamer progressing from the positive electrode to the grounded one is well simulated. At the end of the pulse, the electron temperature and electron number density in the coaxial-type plasma reactor finally reach approximately 1.7 eV and 10-<15> m^<-3>, respectively. During the single pulse, the peak concentration of ozone is approximately 40 ppm near the surface of the glass barrier. Further, in the two-dimensional simulation result, the streamers propagations (1st and 2nd) can be first simulated well numerically.

View full abstract

For improvement of the performance of sterilization in a tube, it is very important to clarify the discharge processes such as electron avalanche and streamer propagation. We clarified the time and spatial evolution of electron number density, electron temperature and number density of chemical species using computational analysis. The distribution of the oxygen atom depends on electron number density and the ozone generates after increasing of oxygen atoms. The electrons diffuse and charge on the interior surface of the tube after the streamer strikes it.

View full abstract

The performance of the surface air-flow induced by non-thermal plasma is studied experimentally. The non-thermal plasma is generated by atmospheric dielectric-barrier discharge. The input discharge power was 1.8W. At first, flow induced by the discharge on a flat plate is investigated. Velocity profile is measured by a hot-wire anemometer. The maximum value 1.1 m/sec was observed on the plate surface. Secondary, separation control for wing surface flow is investigated using a 9cm chord NACA0015 in a wind tunnel at 20m/s of air stream velocity (Re〜1.2x10^5). Barrier discharge electrode is set on the leading edge of the wing. Separation angle is increased by 3.5 degrees and the maximum of the lift coefficient is improved by 12%.

View full abstract

Unsteady control effect of non-thermal plasma on leading edge separation flow was investigated experimentally. Wind tunnel experiment was done using a NACA0015 wing of 9cm chord length under Reynolds number condition of Re=U_∞C/ν=1.2×10^5. A pulse modulated mode with a fundamental frequency of 5kHz was adapted to apply voltage to dielectric-barrier discharge electrodes which were mounted on the leading edge of the wing. First, effect of pulse frequency on separation control was investigated. Second, effect of duty ratio was studied. Finally, FFT characteristic of wake flow under the separation control flow was discussed. An optimum frequency corresponds to St=fc/U_∞=0.47 and 10% duty (discharge power of 0.18W) was found to exist for unsteady excitation of the leading edge separation. FFT analysis result indicates that this optimum unsteady control of the dielectric-barrier discharge has a role as some kind of pacemaker for the separation flow.

View full abstract

The authors have developed a wide heat source by imposing an alternating magnetic field perpendicularly to a transferred arc. In this paper, the deformation of the arc root on the anode is examined theoretically. In a uniform magnetic field, the arc root area increases with the increased arc displacement from the center. The increase of the area decreases the heat flux density. The application of the non-uniform magnetic field is discussed to prevent the decrease of the heat flux density. If the reversed magnetic field is applied to the arc near the anode, the incident angle of the arc to the anode becomes large (close to π/2). In other words, the application of such a non-uniform field might suppress the increase of the area of the arc root. Consequently, it might suppress the decrease of the heat flux density. Theoretical prediction of the effect of the non-uniform field is confirmed experimentally.

View full abstract

An integrated model of compressible flow field, splat formation and coating formation for a cold dynamic spray process has been established. In-flight behavior of micro/nano particles and the interaction between the shock wave and the particles in a supersonic jet flow which impinges onto the substrate is examined. Furthermore, the characteristics of particle acceleration with electrostatic force are clarified in detail by considering viscous drag force, flow acceleration, added mass, gravity, Basset history force, Saffman lift force, Brownian motion, thermophoresis and electrostatic force. The effect of electrostatic acceleration becomes more significant with the decrease in particle diameter even in the presence of unavoidable shock wave. As a result, electrostatic acceleration can broaden the application range of operating particle diameter in a cold gas dynamic spray process to form a robust and activated coating. Finally, based on the integrated model, the coating thickness characteristics in an electrostatic assisted cold dynamic spray process are evaluated.

View full abstract

Characteristics of plasma jets (PJ) of mixed fedstocks were numerically and experimentally investigated. An effect of coexistence of different radicals on ignition delay time was examined by 0-dimensional analysis with full chemistry. The result showed that the ignition delay time did not depend on combination and mixing ratio of radicals initially added to a mixture. Spectroscopic measurements of PJ emissions of mixed feedstocks were carried out to identify chemical species in the PJ and temperature. Temperature of the PJ was successfully obtained by a two-line ratio method of H radicals.

View full abstract

Concentration of produced radical species such as O, O_3, NO and NO_2 by Dielectric Barrier Discharge and the characteristics of air radical flow in the downstream of the discharge region are clarified by the experimental analysis for plasma assisted combustion and ignition. Furthermore, the radical production processes and the behavior of produced radicals at the source of discharge region are analyzed under the high electrical field by numerical analysis.

View full abstract

Ablation experiments of SiC-based materials have been conducted systematically in our laboratory. In this study, physico-chemical phenomena of ablated SiC-based material in high-speed and high-temperature air plasma-jets were investigated. In the experiments, ablation gases spouted out from the SiC-based materials were observed by a high-speed video camera, In addition, radiation from the SiC-based ablation products was measured by a CCD with several kinds of narrow band-pass filter. We obtained spatial distributions of atomic Si lines and CN molecular bands in the ultraviolet wavelength region. Furthermore, spectroscopic measurements in the representative points of the flowfield were performed to investigate the radiative characteristics of SiC-based ablation products in detail.

View full abstract

Passive type MR fluid damper has no electrical devices such as sensor, power supply and power controller, and hence, it has an advantage in reliability and cost compared with conventional MR damper. Moreover, it can automatically adjust the damping force characteristics in response to tits motion. The prototype of the passive type MR damper was designed by using a numerical analysis code for solving MR fluid flow in magnetic field, and it has been manufactured on the basis of the design in order to verify the performance experimentally. This paper introduces the numerical code for its design, the numerical results and the manufactured prototype.

View full abstract

A magnetic viscoelastic material, which consists of viscoelastic silicone gel and dispersed carbonyl iron powder of approximately 7 μm diameter (magnetic micro-particles), has synthesized in order to create highly deformable body under action of magnetic field. Due to high magnetic body force derived from high magnetization character of grain, extremely large deformation of viscoelastic body is expected under strong magnetic field gradient, while keeping solid character of the compound. In the present study, some of mechanical characteristics of the magnetic viscoelastic material are introduced. Opening and closing operation (the aperture control) of a plug placed in a straight tube id performed, and the results of basic experiment are displayed and discussed in connection with applied magnetic field. The results of flow experiment indicate that the material has very fast response character in controlling flow rate.

View full abstract

Magnetic and MR fluids are typical functional fluids. When the magnetic field is applied to these fluids, some of inner particles form clustering structure. These clustering structures influence on the ultrasonic propagation in these fluids. We measured precisely the properties of ultrasonic propagation velocity and attenuation in these fluids subjected to the magnetic field. The measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. Some interesting properties of ultrasonic propagation such as hysteresis are observed. Based on the experimental results, the relationship between these ultrasonic propagation properties and inner structures of these fluids is discussed.

View full abstract

As a fundamental research on the development of liquid crystalline micro actuators, experiments on the liquid crystalline actuator have been performed using a hybrid cell. The nematic liquid crystalline material, 5CB, is placed between two parallel glass plates. The lower glass plate is fixed, and the upper glass plate can move freely. Pulsed voltage of 10 V is applied between the plates, and the movement of the upper glass plate is observed under a microscope. The speeds of the upper glass plate are about 4.3, 26.5, and 54.5 μm/s for 1, 10, and 100 Hz of the pulsed voltage frequency, respectively. It is also found that the liquid crystalline actuator with the hybrid cell can be driven with lower applied voltage than that with the planar cell. Finally, it is concluded that the hybrid cell is available for the liquid crystalline micro actuators, although its efficiency is low in comparison with the planar cell.

View full abstract

Solid like ER characteristic in SmecticA phase of a liquid crystal have been investigated utilizing a parallel-plate type rheometer. Since the smectic liquid crystal has the yield property which is controllable with electric field and temperature conditions, the strength of the alignment structure in the SmecticA phase is experimentally examined from the change in yield stress under various conditions. Direct observation of the yield process was also conducted and it is found that the structure was partially collapsed at the first stage in yield process under the DC electric field. Moreover, it is newly found that the structure in the yield process had partially elastic recoverable strain.

View full abstract

We simulate nematic liquid crystal hydrodynamics by a lattice Boltzmann algorithm. The equations of motion are written in terms of a tensor order parameter. The distribution function is introduced to describe the dynamics of the order parameter. The simulation results of shear flow shows that the nematic order parameter increases, as parameter in the stress tensor is increased. There is an analytical solution for the angle between the direction of flow and the director. The agreement between simulation result and analytical solution is excellent. Although the original LB model is unstable, the FDLBM improves the numerical stability.

View full abstract

This study investigated the effect of the alternating electric field conditions on the generating mechanism of the specific structures of the particle dispersion type functional fluid, which consists of suspended micro scale diamond particles in insulated silicon oil. These specific flow structures contribute actively to a polishing process and to the development of micro fluidic devices. One of the specific flow structure is rotational flow structure formed under high-electric-field intensity and low-frequency conditions. This rotational flow structure is induced by the local accreted flows indicated as the characteristic velocity. The electric field waveform and frequency affects the movements of the local accreted particle that induce the accreted flow between the electrodes. The working time of the electric field is important to generate the accreted flow and the inclination of the electric filed dose not contribute to generate the accreted flow.

View full abstract

This paper presents the capability of the supercritical-fluids simulator (SFS) developed by us to simulate thermal convections of arbitrary substance in arbitrary conditions. In SFS, a numerical method based on the preconditioning method coupled with the PROPATH database is used. The method enables us to calculate not only thermal convections of supercritical fluids but also those of arbitrary substances in gas and liquid phases. As numerical examples, carbon-dioxide, water, nitrogen, methane and helium in a square cavity in several conditions are calculated using SFS and the calculated results are compared with each other and some of them are compared with the existing numerical results.

View full abstract

In order to improve the accuracy of numerical prediction on non-newtonian fluid motion in relation to injection molding, a new scheme is presented here. To describe the interface of two phase, i.e., air and resin, Cahn-Hilliard equation is introduced, and to represent the complex flow passage, IB (immersed boundary) method is applied for both momentum and Cahn-Hilliard equations, respectively. Further since the discontinuity of fluid properties between two phase induces the numerical instability, various type of numerical scheme for the convection terms of governing equations are examined. As result of applying the procedure to a contraction-expansion flow passage, it reveals that the proposed method is able to capture the details of the flow behavior between the air and the resin.

View full abstract

In the melt extrusion process of multi-layer films, interfacial instabilities occurs depending on various parameters which are the difference of rheological properties, thicknesses, or flow rates of each polymer layer and/or the die design. These instabilities cause defective moldings in manufacturing process. We performed viscoelastic flow simulations for multi-layer films and investigated the effect of various parameters on flow fields.

View full abstract

A constitutive equation has been derived Brownian dynamics model of reversible network of FENE dumbbells. In this model, network of polymer molecules is modeled into two fractions (active and dangling) of dumbbells, while creation and destruction of network junctions are represented by association and dissociation processes. We show that with appropriate choice of association and dissociation functions, the newly derived constitutive equation can be used to predict rheological properties of both associative and non associative polymeric fluids.

View full abstract

There are rodlike micelle in surfactant solution occurring by turbulent frictional drag reduction. The theory about the behavior of the rodlike micelle is not elucidated. We focused attention on a recombination phenomenon and studied the theory model of the rodlike micelle and the network structure that rodlike micelle formed. The rodlike micelle was assumed as a rigid rod made up of beads that were lined up. Lennard-Jones potential and soft-sphere potential were employed as the inter-bead potentials for end-end beads and interior-interior beads, respectively. And we analyzed Brownian Dynamics Simulation. As a result, the micellar microstructures and the rheological properties of the surfactant solution at different shear and the first normal stress coefficient showed shear thinning characteristics. The relationship between the rheology and the microstructure of the surfactant solution was revealed. And the recombination phenomenon was seen.

View full abstract

Cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) aqueous solution forms worm like micelles at a certain concentration ratio and shows remarkable viscoelastic properties. This solution causes flow-induced structure change in step shear flow. In this experiment, the flow-induced structure caused by sinusoidal shear flow was investigated. The time-dependent behavior of shear stress, flow birefringence, transmitted light intensity and dichroism was measured. When both shear rate and strain is exceeded the critical value for structure change, the all samples becomes opaque. At the first period, birefringence becomes remarkably large at the all samples with different CTAB/NaSal concentration ratio and some of them shows dichroism which is synchronized with shear rate.

View full abstract

Relaxation time, drag reduction and rheological characteristics of trimethylolethane hydrate slurries treated with surfactants have been investigated. The friction coefficient in a pipe flow of hydrate slurries treated with surfactants was at first measured. From the results, it was found that the effective drag reduction appears in the cases of high surfactant concentration and of high hydrate fraction. This behavior was supported by the viscosity shear-thickening occurrence reported in the previous study. However, the effective drag reduction disappears in the case of low surfactant concentration in spite of the shear-thickening occurrence. On this discrepancy, the relaxation time of the solution was measured. It is found that the critical concentration determined from the relaxation time disappearance well corresponds to limitation of effective drag reduction occurrence.

View full abstract

Recently, the elastic turbulence of non-Newtonian fluids with curved channels has been reported in the very low Reynolds number region. In this paper, we deal with the secondary flow of viscoelastic fluids in multiple curvilinear pipes in the higher Reynolds number region where the centrifugal force is not negligible. As viscoelastic fluids, polyacrylamide (PAA) solutions of 0.025, 0.05 and 0.1 wt% were used. The number of curves was varied from 6 to 60. We found that the reversal secondary flow promoted the fluid mixing for PAA 0.05 and 0.1 wt%.

View full abstract

Penetration flows of polymeric fluid through a Newtonian fluid in a circular tube were experimentally investigated. A polymer solution was injected into an axisymmetric abrupt contraction channel filled with a Newtonian fluid, and replaced the Newtonian fluid. In the present study, a 1.0 wt% aqueous solution of polyacrylamide was used as a polymeric fluid and polydimethylsiloxane was done as a Newtonian fluid. The radius of finger in a downstream tube was analyzed. The radius decreases with increasing the capillary number. Moreover it was found that the width was characterized by the capillary number evaluated with the shear-thinning effect of polymer viscosity.

View full abstract