Organic or metallic dust finely distributed in an oxidizing gas can sustain a deflagration which can even lead to a stable detonation in tubes of sufficient length and diameter. Extensive studies reveal that in corn starch-oxygen mixtures single head spin detonations sevelop which show a similar structure as marginal gaseous detonations. In enriched dust-oxygen mixtures single cell detonations were observed in a tube of 141 mm inside diameter. The structure of the single cell could be deduced from the records of 16 pressure transducers and 16 double response gauges giving the arrival times of the leading shock front and the combustion front. First experiments in a detonation tube on 300 mm inside diameter yielded self-sustained detonations in corn starch air mixtures at 1 bar.

View full abstract

Fluid elastic vibration of tube bundles is one of the most important factors that must be considered in the design of heat exchangers. Since this phenomenon is caused by the interaction between flow and structure, and is hence very complex and sensitive in nature, the design criteria established through many experiments, based on envelopes of the scattered data, have been the only reliable tools for the designers. The authors have developed an accurate CFD technique to solve this moving boundary problem. The fluid elastic vibration problems of two cylinders and a cylinder row are simulated using the CFD technique. The characteristic phenomena of vortex shedding, coupled with two-cylinder motion and fluid elastic instability of a cylinder row are successfully simulated.

View full abstract

The lattice BGK method is applied to the simulation of a two-dimensional laminar flow over a backward-facing step. The method and its incompressible version, as well as the new algorithm for boundary conditions, are described. Quantitative comparisons with experimental and other numerical studies are made for three cases.

View full abstract

The oscillating interfaces of an encapsulated liquid drop, which comprises an outer liquid shell and an inner gas bubble, are studied experimentally and theoretically. Using a sequential production device of encapsulated drops in liquid-liquid-gas systems, the oscillating motions of encapsulated drop interfaces are observed in detail under various flow conditions. To investigate the dynamics of the interface, the oscillations of interfaces are theoretically analyzed using a model assuming small-amplitude oscillation of the interfaces based on the experimental observations. The oscillating mode, frequency and ratio of the inner interface amplitude to outer one of the encapsulated drop are investigated quantitatively. Furthermore, the oscillation frequency o the liquid-liquid interface of the encapsulated drop in the immiscible liquid is experimentally obtained for various liquids. Comparing the theoretical results with the experimental ones, the validity of the theoretical analysis is confirmed.

View full abstract

A numerical method is developed to simulate unsteady axisymmetric flow with a free surface. The method is based on a finite-volume solution of the equations on an orthogonal curvilinear coordinate system. A new iteration technique is used for the boundary condition of the free surface in order to stabilize the solution. The numerical method is applied to the simulation of unsteady motion of a single deformed bubble rising through a quiescent liquid. The numerical results show good quantitative agreement with those of experiments and calculations reported previously by other researchers. In the present study, the transient phenomena of an initially spherical bubble as it reaches the steady state are investigated. It is known experimentally that the rising bubble begins to show an unsteady three-dimensional(spiral or zigzag)motion beyond certain critical Reynolds and Weber numbers. Our numerical results suggest that the growth of axisymmetric shape oscillation causes three-dimensional motions of a rising bubble.

View full abstract

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel. The attenuation and distortion of the compression wave were measured in three Shinkansen tunnels and the results were compared with the numerical values calculated using a second-order TVD scheme. The strength of a compression wave is exponentically attenuated with distance as it propagates along the tunnel in both slab and ballast track tunnels, and the attenuation in the ballast track tunnel is considerably larger than that in the slab track tunnel. In the slab track tunnel, the compression wave is steepened as it propagates, while it spreads in the ballast track tunnel. The criterion for judgment whether the compression wave is steepend or spreads is expressed by the value of acoustic Reynolds number of about 10∼15.

View full abstract

A new cross-correlation method, which is called wavelet cross-correlation analysis and is used to express the statistical cross-correlation of two arbitrary signals in terms of scale and time delay, is proposed and its main properties are presented. By analyzing two test signals, it is shown that wavelet cross-correlation does not have the limitations of classical cross-correlation. As a practical application to fluid mechanics, wavelet cross-correlation is employed to determine the cross-correlation relationships between the x-components of the fluctuation velocities at two points on opposite sides of the centerline amd along the centerline of a plane turbulent jet in terms of period and time delay. In the distributions of the wavelet cross-correlation coefficients, similar structures with various scales are observed instantaneously, and the period of eddy and apparent flapping motions can be determined easily in terms of period and time delay. It is found that the apparent flapping behavior appears first in region with an intermediate period. It is also revealed that a similar structure with a high period consists of similar structures with a low period, i.e., a large eddy contains small eddies.

View full abstract

This paper is concerned with calculating the tangential shear stress and the torque required to turn the inner shaft of concentric annuli having a laminar flow with simultaneously developing tangential and axial boundary layers. The nondimensional governing equations have been numerically solved over a wide range of the annulus radius ratio(N=0.5-0.95)and the ratio of the square of Reynolds number to Taylor number(Re² / Ta=0.3-10). The results clarify the effect of these two controlling parameters(N and Re² / Ta)on the torque and show that the assumption of whole-channel fully developed flow leads to a considerable underestimation of the values of the torque.

View full abstract

A"sublayer-mass flow"method is developed as a new tool for analysis of crossflow separation. It is found that the critical points of sublayer-mass flow are located at the points of convergence of surface streamlines. Thus, the critical points indicate where the flow is separated. This representation can be used to identify the primary and secondary separation points of crossflow separation. This is the first successful capture of crossflow separation points in a three-dimensional flow computation.

View full abstract

Objectives of the present experimental study are to investigate adiabatic efficiencies of a supersonic Faraday MHD(magnetohydrodynamics)generator with cesium-seeded argon and at the same time to achieve a high enthalpy extraction. MHD power generation experiments were carried out with a shock tube facility. The MHD channel has 35 pairs of electrodes and the width between its insulator walls is expanded along the flow direction. Total pressures were measured at the exit of the MHD channel and total pressure losses were evaluated. Furthermore, the adiabatic efficiency was measured for the first time in the present experiments in which an enthalpy extraction ratio of about 10% was achievd. Comparison of these results with those obtained using a disk-type generator indicates that a Faraday generator has higher adiabatic efficiencies at the same enthalpy extraction ratio. The influence of voltage drops on loading parameters and electrical efficiencies is also discussed.

View full abstract

The reaction zone structure of asupersonic flow chemical oxygen-iodine laser(COIL)is simulated solving the two-dimensional Navier-Stokes squations in order to clarify the reaction zone structure and the effects of water vapor condensation precisely. A chemical kinetic model consisting of 10 chemical species and 21 chemical reactions is used to determine the chemical composition of the mixture. The liquid phase is modeled as a number of droplet classes. Each class contains only droplets of a certain range of sizes, which is approximated as one average size. The calculation shows that the I₂ gas injected into the singlet oxygen through a two-dimensional slit mixes very slowly and the small signal gain coefficient is high only in a narrow layer where the mole fraction of I(²P_{1 / 2})reaches a high value. Nonequilibrium condensation takes place during supersonic expansion, generating water droplets whose size much smaller than the wave length of COIL. Condensation reduces the small signal gain coefficient, since the temperature rise caused by latent heat suppresses the generation of I(²P_{1 / 2}).

View full abstract

For a M_∞=0.96 transonic flow past a secant-ogive-cylinder-boattail(SOCBT)projectile with and without porous surface at angles of attack, the thin-layer Navier-Stokes approximation with a modified Baldwin-Lomax turbulence model is employed to evaluate the drag and the lift. Computed results show that the porous surface on the boattail of a SOCBT projectile causes effectively the normal shock at the boattail of a solid-surface SOCBT projectile to become a weaker lambda shock, resulting in reduced drag. As the angle of attack is increased, the lift is enhanced for a SOCBT projectile both with and without porous surface.

View full abstract

Flow mixing in an air conditioning unit for automobiles is studied experimentally in a water tunnel to investigate the mixing mechanisms of flow inside the unit at various mix-door angles. Flow visualization is carried out using tracer particles and the fluorescent dyes illuminated by Ar laser sheet, which allows the simultaneous measurement of velocity and diffusion distributions of the flow mixing in the unit by analyzing the captured color images. The measurement of velocity and diffusion distributions indicates enhanced flow mixing at certain mix-door angles, which is caused by the intense mixing of the main flow and the recirculating heater flow downstream of the mix-door. The temperature distribution measured in a prototype unit supports the mixing characteristics observed in the model unit, suggesting the usefulness of the present image analysis.

View full abstract

A new type of sheath flow chamber with low pressure loss was developed using micro-machining. The chamber was formed by laminating three 100-μm-thick, photoetched, metal plates. The device uses sheath-flow geometry : particles in suspension, which enter the chamber via an axial specimen nozzle, are enveloped by a buffering sheath flow and transported to a square capillary tube with cross-section of 300 μm×300μm. Finite element viscous-flow analysis is used to examine the flow behavior in the quasi-two-dimensional passage configuration which produces the fluid-dynamic focusing flow. Experimental measurement showed a smooth constricted sheath flow, and pressure loss was reduced to one-tenth of that which occurs with conventional glass flow chambers.

View full abstract

A magnetically suspended centrifugal blood pump has no valve and operates differently from a pulsatile heart. Therefore, it is important to understand fluid transient flow in the cardiovascular system which is induced by the change of rotational speed of the pump. First, the unsteady characteristic of the pump is studied and the unsteady factor is shown to be negligible at 1 Hz. Second, stepwise change of the rotational speed of the pump in a mock circulation is studied. On the characteristic curves of pumps and resistances the operating points shift almost as expected. Moreover, from the corresponding variations observed in the flow rate and in the pressure at the inlet and outlet, the compliances and resistances in the circulation are identified.

View full abstract

The stability of time-stepping methods for parabolic differential equations is critical issue. Furthermore, solving such equations with a classical time-stepping approach can be very expensive because many small time steps have to be taken if steep gradients occur in the solution, even if they occur only in a small part of the space domain. In this paper we present a discretization technique in which finite element approximations are used in time and space simultaneously for a relatively large time period called a time slab. The weighted residual process is used to formulate a finite element method for a space-time domain based upon the continuous Galerkin method. This technique may be repeatedly applied to obtain further parts of the solution in subsequent time intervals.

View full abstract

An on-line methodology to solve the inverse heat conduction problems of a hollow cylinder is presented. A new input estimation technique based on the concept of Kalman filtering is developed for estimating unknowns in real time, such as the what of the heat source or the heat flux on the boundary of the hollow cylinder. A recursive relation between the observed value of the residual sequence with unknown heat flux and the theoretical residual sequence of the Kalman filter that assumes known heat flux is formulated. A real time least squares algorithm is derived that uses the residual innovation sequence to compute the magnitude of heat flux. This recursive approach facilitates practical implementation and its capabilities are demonstrated in several typical cases with discontinuous and time-varying heat flux inputs.

View full abstract

Heat transfer coefficients in nucleate pool boiling of five binary mixtures were measured under atmospheric pressure on an upward-facing heated surface for a wide range of heat flux from about 15 percent of the critical heat flux to close to it. Mixtures were : methanol / water, ethanol / water, methanol / ethanol, tehanol / n-butanol, and methanol / benzene. As has been observed in many previous experiments, heat transfer coefficients of mixtures were reduced in comparison with interpolated values between their constituent components. This reduction was a function of the mixture composition and became more pronounced with an increase in heat flux. To provide a simpler and more reliable prediction of heat transfer coefficients of mixtures, Thome correlation was modified so as to include the effect of heat flux in a dimensionless form. A newly developed correlation in this way was verified to predict heat transfer coefficients for the present five mixtures well within ±20 percent accuracy lines.

View full abstract

Experiments were conducted to measure the local heat transfer on an endwall with pin fin array. Heat transfer behavior was examined for the cases of a single pin, a single row, in-line and staggered arrays having six streamwise rows. Thermosensitive liquid crystal film was used to measure the local heat transfer coefficient on the endwall. Neural network was applied for the color-to-temperature transformation of the thermosensitive liquid crystal. Local heat transfer on the endwall having a single row of pin fin was affected by flow acceleration between the pin fins rather than the horseshoe vortex around the pin fin. Therefore, the average Nusselt number exhibited a good correlation to the Reynolds number Re_nax, which was based on the average velocity of the minimum flow area, regardless of the pin fin spacing. For in-line and staggered arrays, the average Nusselt numbers correlated with the Reynolds number Re_maxdecreased with the reduction of the pin fin spacing.

View full abstract

The vibrational energy of molecules in phase-changing processes was studied by measuring the infrared absorption spectra using a Fourier transform infrared(FTIR)spectrometer. IR spectra of(NO)₂(ν₁, ν₄), CO₂(ν₂, ν₃), N₂O(ν₁, ν₂, ν₃), and C₂H₂(ν₃, ν₅)in the gas, cluster, and solid phases were compared. Absorption bands of solid-phase molecules are blue or red shifted from those of gas-phase molecules : but those for the cluster phase are always blue shifted from those for the solid phase. This leads to two kinds of vibrational energy change when the phase changes from gas to solid : blue and red shifts, and red and red shifts of the absorption bands. These results can be explained in terms of the vibrational mechanisms of the ε, σ, and m effects, which characterize the effective potential and mass of molecules.

View full abstract

This paper aims at providing the theoretical basis for the determination of condensation coefficient of vapor by means of a shock tube. Film condensation on the shock-tube endwall behind a reflected shock wave is analysed on the basis of the first author's gasdynamics theory. It is clarified that there exists a transition phenomenon during the growth of a liquid film, that is, the liquid film grows in proportion to time immediately after the reflection of the shock wave, and after a transition time, it grows in proportion to the square root of time. The transition phenomenon between these growths is caused by the change in heat conduction characteristics at the endwall. The reason why condensation coefficient must be determined before the transition is clarified.

View full abstract

The purpose of this study is to develop a method for predicting the thermal sensation of an automobile occupant, and evaluate the prediction method's effectiveness in controlling an automobile heating, ventilating and air conditioning(HVAC)system. The main purpose of a HVAC system is not to keep the temperature constant, but to make people comfortable. This HVAC system was designed to control the interior environment according to the thermal sensation of an occupant, and thus has a direct effect on the occupant's comfort. The thermal sensation level was predicted by a neural network from the interior temperature of the vehicle and facial skin temperature of the occupant. The prediction of the thermal sensation using the neural network was satisfactorily accurate. The HVAC system using the neural network could control the thermal sensation of the occupant and could maintain the occupant's level of comfort even if the air temperature was constant.

View full abstract

A sophisticated software is developed for the calculation of thermodynamic cycle and entropy change in a turbocharged, direct-injection, diesel engine based upon the measured cylinder pressure and shaft encoder output. Assumptions of homogeneous mixture and equilibrium thermodynamic properties for the products of combustion are made and the temporal variation in fluid thermodynamic state is effectively progress in a pseudo quasi-steady manner through a series of adjacent equilibrium states, each separated by a relatively small but finite interval of one-degree crank angle. The thermodynamic properties are calculated by either of two equivalent formulations-equilibrium constants or minimisation of Gibbs free energy, and are expressed in algebraic equations for the partial derivative of internal energy and gas constant with respect to temperature, pressure and equivalence ratio. The effect of engine operating conditions on the thermodynamic cycle is studied. Results show that the dynamic fuel injection timing and hence the ignition delay are strongly dependent on the operating conditions, which explains the reason for incorporating a fuel injection control system in modern vehicular engines for the oprimisation of engine combustion cylcle.

View full abstract