As the first report of liquid crystal flow induced by annihilation of a pair of defects, we have studied the relationship between orientation state of molecules and computation accuracy using the Doi theory, in which the orientation state is described with the orientation distribution function. Computation of the function is a huge task, so that we have approximated the function with a series of spherical harmonic functions in order to reduce the task. The computation accuracy is assumed to depend strongly on both the nematic potential intensity and shear rate. It is found from the numerical results that many terms of spherical harmonic functions are required for the high potential intensity and shear rate because the function becomes steep. In addition, we propose diagrams from which we can easily obtain the necessary number of terms as a function of the potential intensity and shear rate.
The present study performed numerical simulations of a solitary wave propagation problem using a modified surface capturing method, and examined numerical accuracy for applications to free surface flow. The moving free surface was accurately tracked by the modified surface capturing method. Maximum run-up heights in the present study are in good agreement with the previous theoretical, numerical and experimental results. The phase shift qualitatively agrees with theoretical result, while there is a discrepancy between numerical and experimental ones. As compared with the previous method, the modified surface capturing method suppressed the numerical smearing of the free surface which is generated by the numerical diffusions. Furthermore, it was confirmed that the volume error is small and that the conservation property in the present study is greatly improved when the wave is propagating.
The paper investigates the method of improving deposition rate in semiconductor deposition process, while maintaining film thickness uniformity and step coverage in a vertical LPCVD (Low-Pressure Chemical Vapor Deposition) system. In general increasing pressure improves deposition rate, but it decreases uniformity of thickness. The result of experiment and the numerical simulation showed that the non-uniformity of film thickness in high-pressure condition can be improved by controlling flow patterns in the space between wafers. In the molecular flow region (low pressure), the deposition rate and the step coverage were not influenced by the source gas flow rate. In the viscous flow region (high pressure), the step coverage can be improved by increasing source gas flow rate. For the flow the nozzle design and exhaust port location are important. Installation of rings outside of wafers is also effective for the improvement of thickness uniformity.
The purpose of this study is to investigate the nonrepeatable characteristics of fluctuating lift in the case of a square prism. Variation of fluctuating lift with towed distance or swing angle were measured for various attacking angles from 0°to 30°.And the effect of attacking angles on fluctuating lift was evaluated by standard deviation of lift data at specific towed distance or swung angle. Moreover flow visualizations were also carried out to study the flow pattern for different attacking angles. The result of this study shows that attacking angle is helpful to reduce the nonrepeatable characteristics of fluctuating lift most effectively in the case of swing motion.
The characteristics of the development process of an unsteady high-speed gaseous jet were investigated by means of an instantaneous schlieren method. Methane and helium were used as the test gas to examine the effect of molecular weight. The methane is the major component of natural gas, and the helium is the closest gas to hydrogen, where both natural gas and hydrogen would be the future fuels. To measure the jet penetration and the angle, instantaneous schlieren images of the gaseous jet were obtained by using a CCD camera with an image intensifire. It was shown that the jet angle decreases with time. The jet penetration could be predicted by a modified momentum theory considering the jet configuration, the change in the jet angle and the transient characteristics of the injector value. The behavior of the jet development of these gases in the early stage of the injection differed from that of a diesel spray which is a two-phase jet. The jet penetration was not affected by the injection pressure.
This paper examines the effect of sound on the disturbance in the shear layer of a round jet with at a range of sound frequencies, from 200 Hz to 1 000 Hz at intervals of 100 Hz using pure tones and recordings of machines operating at different frequencies. Hot-wire velocity measurements, FFT analysis and flow visualization were used to reveal the shear layer structure. Since round jets are used in industrial applications, their environments are generally noisy, thus it is important to understand how the frequency of background sounds affect shear layer disturbance. When the frequency was varied the maximum disturbance was observed at 500 Hz, which coincides with the predominant frequency of a free jet. Spectral components in harmonics arose via nonlinear interaction as the disturbance moved downstream, and transition from laminar flow to turbulent flow progressed through vortex pairing and collapse. Pure tone and machine generated sound exhibited similar characteristics.
The purpose of this investigation is to clarify the effects of turbulence on aerodynamic noise generation. In order to estimate aerodynamic noise radiated from automobiles and high speed trains in turbulent flow fields, a low-noise turbulence generator for small wind tunnel was developed. The developed generator makes a large turbulent field which has inertial subrange in energy spectrum of turbulence. The noise level of the generator was sufficiently small to estimate the aerodynamic noise from the model of autombiles and high-speed trains. The experimental result showed that unsteady sound was generated by the incoming flow turbulence. And noise levels depend on the scale of turbulence. These results indicated that the active turbulence generator is useful for estimating the aerodynamic noise from automobiles in turbulent flow fields.
The aim of this investigation is to understand the generation mechanism of aero-acoustic feedback noise radiated from rear-view mirrors. In order to clarify the relationship between the velocity fluctuation and radiated noise, correlation in terms of aerodynamic noise and velocity fluctuations were measured in a low-noise wind tunnel. The experimental results showed that noise level of the tonal-noise depended on the ratio of the height of the bump to the thickness of the boundary layer. Strong tonal-noise was generated when the height of the bump was almost equal to 40% of the height of the boundary layer. The tonal-noise level also depended on the length between the trailing-edge of the bump and the edge of rear-view mirror. The frequency of the tonal noise can be calculated by modified Rossiter equation. The tonal-noise was disappeared in the case of the bump was placed at separated boundary layer. It revealed that the seed of the tonal noise was small disturbances generated by the bump on the surface of the rear-view mirror.
To investigate the effect of drag-reducing surfactant on typical elementary motions in turbulent flows, direct numerical simulation was carried out for a pair of streamwise vortices and a single low-speed streak. The surfactant solution was represented by a modified Bird-Carreau model. In surfactant solution, the streamwise vortices were inhibited immediately. On the other hand, the low-speed streak was less affected. Secondary streamwise vortices generated by low-speed streak were inhibited at downstream of surfactant solution. In such a sense, maintainance mechanism of low-speed streak was changed. In order to clarify the factor of modification of the elementary motions in turbulence, the energy budget was estimated. The inhibition of streamwise vortices resulted from strong viscous diffusion due to non-Newtonian effect. The influence of surfactant on the low-speed streak motion is mainly caused by the change in magnitude of energy redistribution. This is an indirect effect of streamwise vortices around a streak.
We measured pressure fluctuations and distributions on the casing wall in a low speed axial-flow fan with relatively large tip clearance to clarify the criteria for a spike-type stall inception. The blade loading at the rotor tip and the tip leakage flow were compared between the two stagger angle settings for the rotor blade. Spikes appeared at the design stagger angle setting, and did not appear at the high stagger-angle setting, which was ten degrees larger than the design value. A rotating instability, which was induced by an interaction among the incoming flow, tip leakage flow, and end-wall backflow, was confirmed near the maximum pressure-rise point at both stagger angle settings. At the design stagger angle, the interface of this interaction became parallel to the leading edge plane. This interaction moreover generated a large end-wall blockage near the leading edge. This blockage developed a leading edge separation on the stalled rotor at the tip, and the leading edge separation then grew into a spike. In contrast, at the high stagger angle, the interface of this interaction did not become parallel to the leading edge plane, and the end-wall blockage was smaller than that at the design stagger angle. The leading edge separation therefore neither developed nor grew into a spike although the rotor blade at the tip stalled. We concluded from these results that the large end-wall blockage induced by the interaction among the incoming flow, tip leakage flow, and end-wall backflow was the main criterion for the spike type stall inception.
It is still very difficult to estimate the axial thrust of pump-turbines or of centrifugal pumps with high accuracy. Here we developed a simple method to calculate the pressure distribution and axial thrust of pumps and turbines for very wide range of Reynolds number. The pressure distribution and the thrust of centribugal pumps are calculated, and their dependency on Reynolds number is discussed. The effect of balancing hole is evaluated. The calculation on the water turbine makes the dependency of the axial thrust and leakage flow-rate on the Reynolds number clear.
An adjoint-based shape optimization method of heat exchanger, which takes into account the heat transfer performance with the pressure loss penalty, is proposed, and its effectiveness is examined through a series of numerical simulation. The undulated heat transfer surface under an isothermal heated condition is optimized based on the variational method with the first derivative of the cost function, which is determined by an adjoint analysis of momentum and heat transfer. When applied to a modeled heat-exchanger passage with a pair of oblique wavy walls, the present optimization method refines the duct shape in a phased manner so as to enhance the wall shear while suppressing the flow separation. It is shown that the j/f factor is further increased by 4% from the best value of the initial obliquely wavy duct. The effects of the wave amplitude, which is initially assumed, upon the shape evolution process are also investigated.
A novel flame temperature measurement technique based on two-line OH planar laser-induced fluorescence (PLIF) is presented. In order to measure temperature of an unsteady flame using a single excitation laser and a single ICCD camera, a new conditional image processing method has been introduced. In this method, ensemble-averaged OH fluorescence intensities at the flame front, which are taken by two excitation lines, are used, and the mean temperature at each streamwise position is calculated. The present thermometry is applied to a methane/air coaxial jet flame, which is actively controlled by periodically driven magnetic flap actuators. The uncertainty interval at 95% coverage is estimated as +130 K and -120 K at the mean flame temperature of 2000 K. The measured mean temperatures of controlled flames coincide with the theoretical adiabatic flame temperatures within the uncertainty intervals. When the stoichiometric mixture is supplied, the mean flame temperature is the highest (-2200K), and thus CO emission is drastically reduced. On the other hand, when a lean flammable limit mixture is supplied, the mean temperature is decreased to 1 600 K, and this results in the increased CO emission.
A micro-bubble injection is one of the most promising techniques of enhancing the heat transfer for laminar natural convections of liquid. However, flow and heat transfer structures for laminar natural convections of water with micro-bubbles have not yet been fully understood. The purpose of this study is to clarify the effects of the micro-bubble injection on the laminar natural convection of water along a vertical heated plate using thermocouples and a Particle Tracking Velocimetry (PTV) technique. The experimental results show that the heat transfer coefficients with micro-bubble injection are higher compared with those without micro-bubble injection as the bubble flow rate increases or the wall heat flux decreases. It is concluded from the velocity measurements that the heat transfer enhancement for the laminar natural convection results from the significant increases in the liquid mean rise velocities and the liquid RMS velocities due to micro-bubble injection.
An experiment was conducted obtain systematic data of particle holdup in a liquid-solid circulating fluidized bed. In the experiment, 2 kinds of riser tube having a diameter of 24 mm and 36 mm were used. Tested particles were of glass and ceramics, and their diameter range was from 2.10 to 4.95 mm. Water at ambient conditions was used as the fluidizing fluid. Particle holdup in the riser tube was measured using the shut-off method. Based on the experimental data, correlations for the drag coefficient and the particle holdup were derived, the latter could reproduce almost all experimental data with an accuracy of 15%. The effect of wall was not recognized within the experimental range, i.e., the particle to the riser tube diameter ratio of less than 0.2. The independent parameters for the flow characteristics were identified.
An experiment was conducted to obtain heat transfer data in liquid-solid circulating fluidized beds. In the experiment, 2 kinds of riser tube having a diameter of 24mm and 12mm were used. Tested particles were of glass and ceramics, and their diameter range was from 2.10 to 4.95mm. Water at ambient conditions was used as the fluidizing fluid. The experimental data showed that the heat transfer coefficient increases gradually with increasing liquid velocity (heat transfer enhanced region), and approaches to the liquid single-phase value. Heat transfer coefficient in the heat transfer enhanced region was found to be a function of the slip verocity between the liquid and the particles. Based on the experimental data, a correlation was proposed to predict the heat transfer coefficient of a liquid-solid circulating fluidized bed, which could reproduce the experimental data with an accuracy of 15%. Comparisons of existing data with the proposed correlation showed also good agreements.
An analytical study has been made on the slip boundary condition at the interface between the porous and fluid layers. We adopt a bank of parallel plates as a porous model, and examine the governing equations for porous media with the aid of the local volume averaging. We can disregard the thermal diffusion term in the macroscopic energy equation for ελf/ (h'l2) <<1 and (1-ε) λs/ (h'l2) <<1, and obtain the similar energy equation to the Darcy's law. Applying the energy equation to the porous and fluid layers, we need the boundary condition for the temperature slip at the interface between the porous and fluid layers. Therefore, we have proposed a new thermal boundary condition which is similar to the Beavers-Joseph velocity-slip condition.
Correlating equations for the film boiling heat transfer from a vertical cylinder of finite-length to atmospheric subcooled water were examined and proposed. The overall heat transfer rate around the cylinder was determined by taking into account each convective heat transfer on the bottom, side and top surfaces of the cylinder. The present prediction method was compared with the experimental data obtained by quenching method. The diameter (D) and length (L) of the cylinder tested in the experiments are 32mm×16mm, 32mm×32mm, 32mm×64mm, 45mm×45mm, 50mm×16mm, 50 mm×32mm and 50mm×64mm. The degree of liquid subcooling was varied from 2 to 30 K. All the experimental data for the aspect ratio with 0.32≤L/D≤2.0 can be correlated within ±15% by the present prediction method. Also, the lower limit of film boiling was discussed in terms of wall heat flux and degree of superheating.
A sonochemistry process reforms heavy fuel oil or solid fuel into lighter liquid fuel. The sonochemistry is originated from the behavior of acoustic cavitation bubbles; the nucleation, growth, and violent collapse. Here, an instantaneous hot spot region with local temperature of several thousand Kelvin and pressure of several hundred Mega-Pascal is generated by the cavitation bubble collapse. This hot-spot causes the decomposition of carbon bond and the removal of nitrogen, aromatic series. The rate of sonochemical reaction is affected by vapor pressure of fuel, and thus is decreased for heavy fuels. Therefore, the authors have proposed the application of sonochemistry into heavy fuel oil mixed with higher volatility fuels, because the mixed fuels can improve volatility characteristics due to formation of two-phase region including both vapor and liquid phases. In this paper, the cavitation behavior of mixed fuel is clarified and the result shows that high efficiency fuel reformulation is accomplished by applying sonochemistry to mixed fuel.
In order to use biodiesel as an ignition fuel on dual fuel diesel engines, the combustion characteristics and exhaust emissions of the dual fuel with rapeseed oil methyl ester and CNG (RCNG) are investigated by comparing to the dual fuel with gas oil and CNG (GCNG). The results show that the operable condition of RCNG is almost the same as that of GCNG. At 100% load the dual fuel diesel engine with RCNG can be operated when the equivalence ratio of the intake premixed CNG is about 0.1 to 0.53. The thermal efficiency of RCNG is almost the same as that of GCNG. RCNG has lower Smoke emissions compared with GCNG although NOx emissions of RCNG is slightly higher than that of GCNG. It is concluded that biodiesel can be used as an ignition fuel on dual fuel diesel engines.
Pressure and temperature behind a detonation wave are extremely high and have a potential to cause serious damages around it. Therefore, it is necessary from safety engineering point of view to decay the detonation wave with short distance from a generation of it. In this study, experiments are conducted in order to investigate behaviors of the detonation wave propagating into two pieces of slits, since the detonation wave might be quenched behind the slits by expansion waves generated at a corner of the slits and this behavior might be applicable to a technique of detonation-arrester. The detonation wave produced in a stoichiometric mixture of hydrogen and oxygen is propagated through the slits and behaviors of it are experimentally investigated by using a technique of pressure measurement, soot track record and high-speed schlieren photography. As a result, when the detonation wave propagated through the slits, a shock wave is decoupled with a reaction front. Two shock waves diffracted from the slits interact each other at center behind the slits, then this shock wave interaction induces a hot-spot enough to cause local explosion. Since, the shock wave is reflected from a tube-wall eventually, the detonation wave is re-initiated by mechanisms of shock-shock interaction or shock-wall interactions.
A numerical analysis with a detail description of flow dynamics and chemical kinetics on the effect of the equivalence ratio of methane/air mixtures on the minimum ignition energy is carried out. In the early stage, the behavior of the flame kernel is dominated by a flow which is induced by the blast wave. Although a high temperature gas, which spurts out from the electrode gap, quenches, the gas at the electrode gap is self-sustained with an application of small ignition energy near the minimum. After a certain period of time, the flame kernel gradually grows out of the electrode gap. In the case of high-energy application, hot gas region, which spurts out from the electrode gap, doesn't quenches and propagatable flame kernel is formed at the early stage of spark ignition process. The local equivalence ratio at the electrode gap is larger than that in the outer region with an application of small energy although its effect is not so strong in an application of high energy. In addition, calculated profile of the minimum ignition energy as a function of the equivalence ratio for methane-air mixtures shows a minimum value below the equialence ratio of 1.0. An effect of preferential diffusion for lighter molecules is confirmed.
It is important to measure heat flux from the burnt gas to the combustion chamber because of the improvement of the efficiency of an engine. Instantaneous heat flux of S. I. Engine is usually measured using a thin film type of heat flux sensor. But there is a significant difference of outputs among heat flux sensors on the market. In this study, some types of heat flux sensors are produced and evaluated by experiments using a constant volume vessel. To confirm the accuracy of each type of sensor, the wall side heat flux which is average of heat fluxes from same type of heat flux sensors installed in the vessel, is compared with the gas side heat flux which is calculated from the change of pressure in the combustion vessel. The results show that the wall side heat fluxes obtained by sensors which produced obeying the law of thermocouple are agree with the gas side heat flux. It is found that the plating film should be the same metal to the wire of sensor. Furthermore, measuring for the transient component of the heat flux, it is not necessarily for the body of a heat flux sensor to use the same material of the combustion wall.
The state of heat loss from combustion gas to combustion chamber walls during the cycle in an internal combustion engine can be evaluated from instantaneous surface temperature of the walls measured by thin-film thermocouples (TFTs). Not only a suitable temperature probe but also an appropriate measurement system is necessary for accurate measurement.TFTs developed by the authors' group were designed and fabricated so that disturbance of the temperature filed could be minimized when they were embedded into combustion chamber walls. Appropriate measurement circuits and devices are necessary for accurate measurement of thermoelectromotive force generated by the TFTs because it changes very quickly as the crank angle, and the amplitude of its fluctuation is considerably small, usualy less than 3 mV. Therefore, the authors' group established a measurement system which consists of measurement circuits of thermoelectromotive force, an A/D (analog to digital conversion) system and a data processing device. The authors' measurement circuit has an advantage of being noise-free and quick in switching channels. On the other hand, the A/D system is of high accuracy and synchronizes with the engine operation. Furthermore, meaningfully reproductive data is generated by the data processing device. In this report, the authors' measurement system is presented.
A pilot-scale PPCP (Pulse corona induced Plasma Chemical Process) system for controlling gas-phase dioxins and NOx was installed in the incineration plant. The gas flow rate was varied up to 5000 Nm3/h, branched out from the existing duct. The PPCP reactor consisted of 18 tubes in a wire-cylinder configuration, energized by a 50 kW PPCP pulse generator. The decomposition efficiency for dioxins in TEQ base was more than 85% with 3-6 Wh/m3. The NO to NO2 conversion was more than 93%. Then, 50 Nm3/h of the flue gas was introduced to the chemical reactor using Na2SO3 solution, resulting in more than 90% of NOx reduction with negligible by-products such as NO-2 or NO-3 ions.