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A numerical analysis of the transient convective flow and heat transfer on a horizontal isothermal rotating disk is presented. Simulation is carried out by solving the axisymmetric Navier-Stokes equation adhering to the Boussinesq approximation coupled to the energy equation for three Rayleigh numbers Ra = 8.4×10^3, 6.7×10^4, and 5.4×10^5, and varying Reynolds number (up to 1.03×10^4) as parameters. This paper describes isotherms, flow patterns on the isothermal rotating disk, and velocity vectors at the γ-z plane, as well as local heat transfer profile and the comparison of the average Nusselt numbers to Wagner's theoretical approximation. Numerical results demonstrate that the transient mixed convection flow and heat transfer take a minimum value by a certain Reynolds number at given Ra.

The present paper describes the active method for controlling vortex shedding from a circular cylinder in uniform flow. The cylinder motion in the cross-flow direction is controlled by the reference velocity signal in the wake with some phase lag, with the aim of reducing vortex shedding from the circular cylinder. The effectiveness of this method is studied by wind-tunnel experiments with flow measurement and visualization. All the results indicate that the reference velocity in the wake is weakened by active control at the optimum phase lag and is strengthened at the reverse phase lag. A similar reduction and enhancement in the velocity fluctuations in the wake with this control at these phase lags is observed in the flow measurement in the cross section of the wake, and is also cofirmed in the whole flow-field visualization study by the smoke-wire method with a laser-sheet technique. These results suggest the possibility of reduction of vortex shedding from a circular cylinder and modification of the wake by the present active control method.

The present paper describes a new active method for controlling vortex shedding from a circular cylinder in a uniform flow, using rotary cylinder oscillations controlled by the reference velocity signal in the wake with some phase lag. The effectiveness of this active method is evaluated by measuring the response of mean and fluctuating velocities in the cylinder wake and by visualizing the flow field around the cylinder. It is found that velocity fluctuations are reduced by the control at the optimum phase lag, while they are enhanced at the reverse phase. The maximum reduction of 30 percent in the reference velocity fluctuations is obtained with the optimum control, where the optimum value of phase lag and the feedback coefficient are adopted. The modification of the mean velocity profile and the reduction in the fluctuating velocities in the wake are measured under the optimum control and the corresponding variations in the visualized flow field are recognized, similar to the change observed under the control with cross-flow cylinder oscillations.

This paper described the visualization on the behavior of bubbles near a blowing nozzle in a pressurized fluidized bed. Experimental study for understanding the characteristics such as the size and interval period of bubble nucleus in the pressurized gas fluidized beds were carried out with recording image pictures taken by high speed video camera (HSV-1000). As the results from image analysis we found the bubble size decreased and the bubble shape varied with the pressure increased, also seemingly the bubble shape was strongly influenced by particle size and the bubble frequency slightly increased with pressure incseased. Also a history of bubble growth was shown clearly.

Repulsive magnetic levitation systems with magnets driven by actuators were studied in this paper. In one system, a levitation magnet was driven in the direction of repulsive force to control the position and vibration of the levitated object. In another, a levitation magnet was moved in the lateral directions to stabilize the system in the manner of an inverted pendulum. The first type was studied experimentally with an experimental setup using a magnetostrictive actuator. The damping characteristic was modified well by driving the actuator in proportion to the velocity of the levitated object. The I-PD control was adopted for obtaining desired characteristics of floating position control and active damping of vibration.

This paper describes the suppression of torsional vibrations of a rotor by a hollow cylinder partially filled with liquid. The hollow cylinder is divided into identical sections by radial walls. The numbers of sections of the hollow cylinders are 3, 6, and 8. Tuning conditions for fill ratios are examined. Surface waves are also obeserved for the cylinder with 3 sections. Accordingly, observed surface waves move backward, that is, they travel in the opposite direction of the rotation. Analysis including the Coriolis force is presented. Analytical results show good agreement with the experimental ones.

Acoustic streaming is generated by Reynolds stress in the sense of mean acoustic momentum flux in a sound field. In the case of an acoustic standing wave produced by an air column oscillation in a closed duct, the friction and the Reynolds stress in the resulting Stokes layer are the essentials of acoustic streaming generation in the vicinity of the duct wall. The thickness of the Stokes layer decreases with the oscillatory Reynolds number. The plane wave propagation in the duct is assumed for the case of high Reynolds number except for the thin Stokes layer adjacent to the duct wall. The velocity profiles of the streaming are estimated theoretically from the steady component of the second-order term of a perturbation expansion in which the first-order approximation is a sinusoidal oscillation of the air column with plane waves. The present paper describes theoretical analysis of the velocity profiles of the acoustic streaming in the Stokes layer by means of the matched asymptotic expansion method. The results obtained show the existence of reverse streaming in a very thin layer adjacent to the wall and the effects of thermal boundary conditions at the wall on the velocity profiles of acoustic streaming in the Stokes layer.

In this paper, we propose a high performance receiver architecture for wireless communication systems, such as Bluetooth. This architecture uses a subsampling mixer and a delta-sigma modulator. The proposed sub-sampling mixer has complex band-pass characteristics. The band-pass filter suppresses the aliasing noise generated by the subsampling mixer. The proposed discrete time delta-sigma modulator has an up-conversion mixer and a down-conversion mixer. An intermediate frequency signal converted from a radio frequency by the subsampling mixer is inputted into the delta-sigma modulator. The delta-sigma modulator input signal is converted to a baseband signal by the internal mixer. After that the baseband analog signal is converted to a digital signal.

Let $X$ be a compact metric space and $Y$ a stratifiable space. By $C(X, Y)$, we denote the space of continuous maps from $X$ to $Y$ with the compact-open topology. In general, $C(X, Y)$ is not stratifiable. In this paper, we show that $C(X, Y)$ is stratifiable if $Y$ satisfies the condition given by Mizokami [Mi]. And we construct a stratifiable space $Y$ such that $C(X, Y)$ is not stratifiable even if $X$ is countable and compact.

It is the purpose of this paper to make clear the cause for the considerable dispersion of inertia and drag coefficients of a circuler cylinder in a sinusoidally oscillating flow at low values of Keulegan-Carpenter's number. Drag and lift forces are measured by cantilever beam system with four PN semi-conductor gages simultaneously. The flow around a circuler cylinder are visualised by electrolysis. The following properties became evident after examining the experimental results. In the case of the process from production to shedding of eddy is symmetric with respect to a line of mainflow passes through a cylinder axis, the drag and resultant force coefficients shows a value about 2 times as mach of asymmetric formation of eddy at same K-C number. Asymmetric formation of eddy plays an important role to change the direction and magnitude of approaching velocity. As a result of these, it induce strong lift and decrease of drag and resultant forces.

It is the purpose of this paper to make clear the change of fluid forces and pressure distribution along the surface of circular cylinder with the change of distance between circular cylinder and plane wall, and vortex shedding from a circular cylinder. We measured of fluid forces acting on a circular cylinder in the Reynolds number range of (10)^4 to 7×(10)^4 and pressure distribution along the surface of circular cylinder at the Reynolds number of 7×(10)^4. The following properties became evident often examining the experimental results. The Strouhal number calculated from the variation of lift in the region of spacing ratio Y/D=0~0.3 are nearly zero. The physical meaning of these fact is considered to be formation of separation region behind a circular cylinder. In region of the distance between a circuler cylinder and plane wall Y/D=0~0.7,position of stagnation point separation are influenced considerably by the spacing ratio. And in the case of Y/D>2,it can be consider that there is no effect of wall.

The Japan Aerospace Exploration Agency launched the S-310-43 sounding rocket from the Uchinoura Space Center on Aug. 04, 2014 for the purpose of investigating such behavior as boiling and flow of cryogenic liquid rocket propellant in an environment simulating coasting flight on orbit by using the sounding rocket's sub-orbital ballistic flight. In the low-gravity state, the cryogenic fluid (liquid nitrogen) was introduced into the test sections of similar shapes to the flow channels in the cryogenic propulsion systems. The boiling of liquid nitrogen inside the test-sections and the transition of flow regimes from gas/liquid two-phase flow to liquid mono-phase flow were visualized. The temperatures, pressures and void fractions of each channels were measured as well. Development of the experimental equipment for S-310-43 sounding rocket is described in this paper., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: DS1540301003

A numerical analysis for natural convection heat transfer in eccentric cylindrical annuli was presented. This problem is one of the most basic problems for a shell and tube-type heat exchanger. Many studies on heat transfer in eccentric cylindrical annuli on the view of flow pattern have been done, however, only a few studies on the effect of eccentricity on heat transfer enhancement have been conducted. The numerical method presented in this paper utilized the boundary-fixing method which is applicable to the moving boundary problem. Calculations are made for isotherms, streamlines, dimensionless Nusselt number distribution around the cylinder, and dimensionless total heat transfer. The effects of eccentricity on heat transfer enhancement and convection mechanism in eccentric cylindrical annuli are presented.

We introduced theoretical formulae in order to predict the noise and the pressure head of bladed multiple-disk fans and verified the validity of these formulae by experiment. In present investigation, we assumed that the characteristics of the fans could be consisted of two parts; one is the disks and another is the blades, and that the total pressure head and the sound pressure level could be estimated by the sum of these parts. Assuming the noises due to the turbulent boundary layer on the disk surface and the vortex shedding from the trailing edge of a blade were independent of each other, the sound power estimation was carried out. In this paper, it was examined the effects to the aerodynamic characteristics and the fan turbulent noise of parameters; the span length of the blade, the number of blades, the inner radius of impeller and the setting angle of the blade. Moreover, the comparison between the theoretical and the experimental values was tried. The agreement between the theoretical and the experimental results was fairly well., 長崎大学工学部研究報告, 24(43), pp.109-116; 1994

This paper deals with solidification and flow characteristics of high-density polyethylene plastics as polymer plastics in a narrow annular cavity cooled on an inner circular tube. The experiments are carried out with various parameters (plastics temperature, flow velocity of the plastics and cooling surface temperature). The obtained results show that the solidification layer formation of polymer plastics is affected by flow behavior and viscosity of molten polymer plastics. The useful dimensionless equations for predicting the amount of polymer plastics and the time of finishing the injection of the polymer plastics into the cavity are derived as a function of Reynolds number, cooling temperature ratio and Stefan number., 一般に、家電製品、自動車部品に多用されているプラスチック製品の大部分は、生産性の良さや複雑な形状のものが容易に成形できる特徴を有する射出成形法により作られている。射出成形法は、その成形プロセスにおいて、高温・高圧のプラスチックを急冷して成形するために、充填不良、”そり”、”ひけ”などの問題がしばしば起こるようである。近年、これらの諸問題の解決として、コンピュータを利用した数値シミュレーション手法により、流動プラスチックの凝固特性を予想する各種解析の試みがなされている。しかしながら、狭い空間でのプラスチックの流動、凝固現象の詳細な把握は十分になされていない現状にある。平井らは、二次元矩形ダクト内の流動プラスチックの凝固過程を、最初に冷却面上に形成されるスキン層と流動停止に伴って成長するコア層の凝固に分類し、特にスキン層の凝固現象が成形品の変形に大きな影響を与えることを数値計算により解明している。一方、黒崎らは、矩形キャビティ状金型内のプラスチック凝固に伴う残留応力をレーザー光照射によるプラスチック固-液相間の複雑屈折を利用した方法により測定し、金型内のプラスチックに発生する様々な応力関係を解明した。さらに吉井・金田は、近赤外光弾性法によるプラスチック成形品の残留応力の測定により、金型内のプラスチックの流動と冷却条件が、その成形品の性質に大きく影響を及ぼすことを明らかにしている。このように従来の研究において、金型内での高圧高温状態における成形物の残留応力解明に焦点を絞ったものが大部分であり、最も基本的な流動プラスチック樹脂の凝固現象を伝熱学的そして流体力学的立場より検討したものは少ないようである。本研究は、2重円管間に形成される狭い円環状空隙に、溶融プラスチックを下部より流動させ、円筒内壁より冷却させた場合の凝固現象を、流動凝固挙動の可視化観察、圧力変化そして凝固位置および凝固量の実測結果より解明するものである。本実験においては、大気圧より少し高い低圧力状態で溶融プラスチックを押込み低速流動を行うことにより、時間とともに徐々に冷却面近傍でのスキン凝固層の形成およびコア凝固層の成長の基本的挙動を明らかにするものである。従って本研究で取り上げられる低圧成形は一般に行われている高圧高速成形の際に発生する流動プラスチック樹脂の摩擦熱の発生は伴わないものである。本研究は、狭い空隙での流動凝固現象を基礎的に把握しようとするもので、実験パラメータとして溶融プラスチックの押込圧力、温度、流速そして冷却面温度を取り上げてある。最終的には、円環状空隙に流入するプラスチック量と流入完了に至るまでの時間を種々の無次元量にて整理した無次元式を提案するものである。

This paper describes the experimental study on suppression of torsional vibrations of a rotor by attaching a hollow cylinder partially filled with liquid. The hollow cylinder is divided into identical sectors by radial walls. In addition to measuring torsional vibration, surface waves were photographed to observe the motion of the contained liquid. The number of divisions of tested hollow cylinders is 2 or 4. Experimental results show that the surface waves move backward, that is, travel in the direction opposite the rotation.

The present paper was concerned with a part of the series of study on the expansion channel flow by authors. The laminar flow in a two-dimensional asymmetric and symmetric expansion channel has been investigated numerically. As a computational model of the asymmetric expansion channel, the two-dimensional channel with backward facing steps on both upper and lower walls were considered, and both steps of upper and lower walls were placed at different location with distance LD in the flow direction. Two-dimensional time-dependent Navier-Stokes equations were solved by the finite difference method. For the LD=0.0 (symmetric expansion channel) and LD=1.0 (asymmetric expansion channel), calculations were performed by the pseudo-unsteady method to obtain the steady solution as t→∞. In this report, behaviors of flow pattern, vorticity at wall and pressure gradient with passage of time were presented.

This paper reports experimental results of reinforced concrete L-shaped section shear walls with varying horizontal loading direction. The deforming directions of the walls subject to horizontal forces are five directions dividing the angle of the weak axis from the strong axis into four equal angles. The results are as follows : (1) Initial stiffness and cracking loads remarkably change with varying deforming direction. (2) The flexural strength can be calculated by the eq. (3), considering the projected position of steel after projecting L-shaped section on a line of deforming .direction. (3) Each shear strength of two walls of L-shaped section shear walls decreases as the out-of-plane deformation becomes larger.

It is well known that the secondary flow can be observed in a straight open channel, however, it is elusive to be detected because of its small magnitude and unstableness. The secondary flow is investigated experimentally or numerically by many researchers. In this paper vortex motions induced by the secondary flow are classified on the basis of its cause; velocity gap, flow boundary and bed-generated turbulence, and discussed by using the results of 3-D LDA measurements, flow visualization in a transverse cross section and an algebraic stress model (Naot-Rodi model). It is found that there are some difference between the time-mean secondary flow obtained by LDA and N-R model and the instanteneous secondary flow by the flow visualization.

Some hydrodynamic aspects of tidal inlet defined as the relatively short channel connecting bay and ocean is treated. Often such system exhibits irregular geometry and complicated flow patterns at the ocean- and bay-side. As a result of the large variations in depth and width, the velocity field contains both vertical and horizontal eddies. These eddies often are dominant features rather than perturbations on the main flow.In the context of this paper, an idealized and simple model basin is treated. It is because that this research is aimed to improve the fundamental understanding for the inlet-related problems.Only tidal forcing is considered. Emphasis is on the bay response of water level to outer sea, tidal exchange process through the inlet and local sea-bed variations near the inlet.

This paper presents finite element method for the Navie-Stokes equations of incompressible viscous flow. For the spatial descretization, we propose a new interpolation scheme with enhanced rotatinal field. As a numerical example, two dimensional cabity flow problems are examined by traditional and proposed schemes.

The present paper proposes a new stereo pair matching technique with correction of light refraction at water-air boundary using two video pictures and a new particle tracking algorithm for three-dimensional particle-tracking velocimetry (3D PTV) based on a cross-correlation method using two-consecutive-time-step binary pictures. The technique of 3D PTV is applied to measure three-dimensional velocity vectors of tracer particle motion in a cylindrical water vessel with a bottom blowing bubbling jet. The performance of stereo pair matching and the measurement results of the bubble-water two-phase flows are discussed,and as a result the proposed technique is shown to be useful in measuring the three-dimensional bubbling jet flow field.

This paper reports the numerical results on the effects of numerical parameters and the numerical methods of unsteady pressure in a discrete vortex method combined with a panel one. Calulations are carried out for a separated flow around a two-dimensional square cylinder. Results are as follows; Global flow characteristics are little affected by the shedding time interval of nascent vortex and the length of panel. In unsteady pressure calculation, it is important to estimate the effect of rascent vortex.

The present paper deals with the flow of a viscoelastic fluid past a rectangular cylinder placed in the center of two parallel side-wall channel. The viscoelastic fiuid is modeled by Maxwcll's constitutive equation. The flow field around the rectangular cylinder is numerically solved by the finite differcnce rnethod. The effccts of several factors on the streamline pattern were discussed in the range of Re = 10～100,We =1.0, H/B = 2～4 and L/B = 1～3. For the Newtonianfluid,it was confirmed that rear rwin vortices of the cylinder increased with an incrcase of the Reynolds number (Re) and the cxpansion of streamlines in the vicinity of the cylinder was suppressed by the approach of the channel side-walls to the cylinder. Next,it was found in the viscoelastic fluid that front twin vortices of the cylinder were born and grew under a certain condition. This front vortex region seems to be due to the combined effect of the fluid elasticity (We) and the channel side-walls (H/B). Besides,it was shown that the geometry of rectangular cylinders (L/B) infiuenced on the flow field of the viscoelastic fluid in the casc of the longest cylinder (L/B = 3) and its effect weakened with an increasc of thc fiow inertia(Re).

In the present paper, we assume the swirling motion of tatsumaki as the Rankine vortex moving with a constant velocity and analyze the unsteady horizontal flow at any point in the tatsumaki path.The inertial force on bodies due to the action of unstady/ accelerating flow is obtained by using the velocity potential for inviscid flow. The inertial force and the drag which is dependent on the square of the fluid velocity may be combined with the Morison's equation, which constitutes the total fluid force.The results are discussed and examined, comparing to the steady-state wind loadings with a constant velocity.

An experimental study[1] was conducted to determine the dynamic characteristics of surface-floating particles in liquids flowing in a two-dimensional, semicircular open channel. A modified dynamic(Basset-Boussinesq-Oseen) equation was derived. It is disclosed that the dynamic characteristics (or traceability) of such a surface-floating particle is governed by a dimensionless parameter, i.e. dimensionless time t_* divided by drag coefficient Cd. In this paper, the motion of surface-floating particles at various flows in a straight and a curved channel is experimentally and numerically studied. The purpose of this study is to confirm the validity of the modified B.B.O. equation and to investigate the role of the dimensionless parameter t_*/Cd in particle tracing.

Several metods for eddy current analysis of thin conducting plates have been developed. The eddy current analysis can be performed by an integro-differential method using an electric vector potential. The integro-differential method is formulated as a differential equation by a finite element scheme where the impressed magnetic flux density and the induced magnetic flux density are evaluated by integral terms. In this paper, a method for eddy current analysis of thin conducting plates taking account of the source currents in the conductors is proposed. An electric scalar potential is introduced for the analysis of source current distribution and the distribution of the scalar potential is calculated by a 2-D finite element method which expanded to 3-D arrangement of the thin plates. The formulatios for the electric vector potential and the electric scalar potential are shown and the applicability of the proposed method is verified by using experimental models.

In a core wall system high-rise building, the center core of which consists of four L-shaped core walls, under the action of a diagonal seismic force, the axial load of the core wall is very high. Particularly the corner and the area near the corner of the L-shaped core wall are subject to high compressive stress. Reinforcing these areas is therefore considered effective in improving the deformation capacity of the core walls. In this paper, Eccentric compression tests and central compression tests were conducted on rectangular sections of columns which simulated the corner and the area near the corner of the L-shaped core wall.

It is not guaranteed for most of shock capturing schemes to obtain a physically relevant solution for complicated multi dimensional flow with shock wave reflection and crossing, such as steady Mach reflection. Ability of most of shock capturing schemes to simulate the steady Mach reflection has not been studied well because of the lack of solution for the steady Mach reflection in the large sense, i.e., not the solution for the vicinity of triple point, but for the whole Mach reflection flow region. In this paper, our analytical solution in the large sense is presented, and is used to study the ability of shock capturing scheme of the steady Mach reflection. Two inviscid flow simulations were made with the Harten-Yee type TVD scheme. The slip line configurations and the flows behind Mach stem by the scheme fairly agreed with the analytical ones, but the detailed flow structure, particularly around the triple point, did not agree well with the analytical solution., 資料番号: NALSP0016036, レポート番号: NAL SP-16

The flow fields over interior and exterior of simplified SCRAM jet model are simulated numerically by 2-Dimensional Navier-Stokes equations using an implicit finite difference scheme. For these simulations, the numerical scheme based on Chakravarthy-Osher's TVD formulation is improved for multi grid application and Simple & Robust wall boundary conditions are applied. In this paper, the computed results are compared with two kinds of experiments, one is conducted by high speed wind tunnel and the other is conducted by hydraulic tank., 資料番号: NALSP0016045, レポート番号: NAL SP-16

The Smagorinsky model has been commonly used in large eddy simulation (LES) of turbulent flow. Although LES computations or a variety of flows using this model have yielded acceptable results, it was necessary to incorporate several modifications into the model: a)the model constant was optimized in different flows, b)the damping function was used to account for near-wall effects. These modifications were generally ad hoc. Besides, a poor correlation of Reynolds stress model value with the direct numerical simulation (DNS) exact value was reported. The resented paper's major objective is to address these issues and propose a new model which mitigates previous model's drawbacks by determining the proper energy scale in the subgrid scale eddy viscosity coefficient correlating with the channel flow DNS data., 資料番号: NALSP0016001, レポート番号: NAL SP-16

The objective of this paper is to compute the expansion of a supersonic flow through an internal-external nozzle and its interaction with the supersonic flow of free stream air. Furthermore, we are also attempting to calculate thrust and lift for a scramjet nozzle. The governing equations are the Navier-Stokes equations for two-dimensional flows. The finite difference scheme employs an implicit upwind scheme. A turbulent model is adapted to the Baldwin-Lomax model. The diffusion, reaction and radiation of gas is neglected. Calculations are performed for the cases that have Mach number, temperature and pressure range at the combustor exit of 3,200 degrees K and 1 to 2 atmospheres respectively. The values on the outside of the afterbody and cowl are 3,500 degrees K and 0.1 to 1 atmospheres respectively. The effects on the flow field, thrust and lift due to change of pressure, velocity and nozzle shape are studied. The results of the numerical calculations give different flow fields for underexpansion or overexpansion at the cowl exit. Consequently, we found that the patterns of an asymmetric nozzle flow were fixed by the degree of expansion at the cowl exit and that no perfect correct expansion existed in these flows. Furthermore, we found that the internal flow of the nozzle in case of the overexpansion was largely influenced by the flow of free stream air., 資料番号: NALSP0016026, レポート番号: NAL SP-16

It is known that the vibration of plate girder generates undesirable acoustic radiation and/or fatigue failure at the welded joint connecting web and flange plate under travelling train. In this paper, natural vibrations and natural modes of I-section and box-section members are analyzed using finite strip method. The governing equilibrium equation is derived taking into account that the natural vibration mentioned above may be transformed into the wave propagation of sine wave. Numerical results are compared with the wave propagation in the plate elements comprised in thin-walled members, and the characteristics of wave propagation in thin-walled members are discussed.

Numerical simulation for the cascade of aeroengine is usually done about circumferentical same airfoils and is one-pitch calculation. but in the real engine there are little changed airfoil or structures between cascade. So, we extended one-pitch calculation code to multiple-pitch and named it analysis of non-uniform airfoil cascade. In this paper we use this code to bypass duct of a commercial jet engine and get good agreement between analysis and experiment., 資料番号: NALSP0016037, レポート番号: NAL SP-16

In this paper, numerical analysis of laminarization phenomena of strongly heated gas flows within concentric annular tube was performed and an improvement of the Reynolds stress turbulence model is proposed. In the first part, the Reynolds stress model proposed by Launder and Shima was tested in its original form. Numerical results show that the main features of laminarizing flows such as a change in time averaged velocity profiles and the reduction in turbulent kinetic energy can be reproduced to a certain extent. However, it was also found that if the heating rate is relatively low, the prediction efficiency of local Nusselt numbers are considerably poorer than expected. Therefore, it was anticipated that there remains much for the improvement of the original model particularly for the low Reynolds number region. Following these results, an attempt was made to improve the model by reforming the shape of the empirical function that appears there for taking into account the effects of the wa11. The modified model was applied to the case of relatively low heating rate and the considerable betterment was achieved.

In order to investigate the mechanism of wall turbulence generation, we have been studying a subcritical transition in a flat-plate boundary layer experimentally, through observing its nonlinear response to energetic hairpin eddies acoustically excited near the leading edge of boundary-layer plate. In this paper, our recent results on the development of wall turbulence structure in this transition is presented to reveal that the break-up of three-dimensional wall shear layers (with streamwise vortices) into hairpin eddies leads to wall turbulence. The effect of riblets on the development of wall turbulence is also reported and discussed., 資料番号: NALSP0015015, レポート番号: NAL SP-15

On the boundary-layer receptivity, the present paper describes the results of numerical simulations and laboratory experiments to clarify the condition under which external disturbances such as sound and free-stream turbulence can excite Tollmien-Schlichting waves. The most important finding is that the unsteady pressure gradient on the wall imposed by the external disturbance need to have such proper spatial scales as to match lambdaTS, the wavelength of T-S wave to be excited In this case, the unsteady pressure gradient induces the vortical wave of the proper scale and then Tollmien-Schlichting wave., 資料番号: NALSP0015005, レポート番号: NAL SP-15

The oscillatory characteristics of a pseudo-shock wave with an incoming Mach number of 1.75 in a rectangular straight duct are experimentally investigated by static pressure measurements both on the duct axis and on the wall surface. Statistical analysis is applied to the detailed fluctuating pressure data in the pseudo-shock region. The correlation between the oscillatory characteristics and the flow mechanism of the pseudo-shock wave is also discussed in detail in the last part of the present paper.

In the previous paper^1)- the authors presented a bed-load equation which was derived from their constitutive relations of debris flow. The equation underestimates somewhat the bed-load rate in the range of non-dimensional shear stress smaller than 0.2.This paper discusses a refinement of the constitutive equations in smaller range of shear stress, but greater than the critical value of initiation of sediment movement.A bed-load equation, then, is derived from the refined constitutive relations.The formula is tested in terms of the data obtained from flume tests carried by using both of sand particles and glass beads.

For the design of aeronautical vehicles, it is necessary to predict not only steady aerodynamic characteristics but also unsteady ones. However, current numerical tools for the latter are insufficient especially in the case of supersonic flow. In this paper, mathematical formulation of a boundary-element-type panel method is achieved for supersonic unsteady flow calculations. Linearized Euler equation is transformed to an integral form, which is partially simplified according to Morino's method. The integral equation is discretized to a linear algebraic equation by raplacing the boundary surface with an assembly of triangular panels. To ensure the continuity of doublet density on panel edges, linearly varying distribution is adopted on each panel. The shape of the panel assembly and its attitude can be specified arbitrarily within the limit of linearization validness, which enlarges the ability of this method compared to the current panel method programs for supersonic unsteady flow.

Numerical simulations of turbulent boundary layer over a step change in surface roughness are performed using a refined k-εturbulence model. The model derives from the Navier Stokes equations by the time space averaging in consideration of the drag effect by roughness elements and volume change of roughness elements. Comparison between calculations and experimental data shows the applicability of the numerical method presended in this paper. Finally the variations of the flow over a step change in surface roughness are examined using the calculated values.

The Navier-Stokes equations and the continuity equation express conservation of momentum and mass, respectively. Therefore, numerical schemes to solve these equations have to conserve these quantity numerically to get accurate solution. For simulations of turbulent flows, various kinds of turbulence model are commonly introduced in the numerical scheme. Some models are used with the wall function method, which can reduce computing costs drastically. This, however, may violate the above mentioned conservation property, because the governing equations are not solved in the region where the wall function method is applied. In the present paper, the wall function method with conservation property is proposed. The numerical fluxes on and adjacent to the wall are determined such that the wall shear stress obtained from the law of the wal1 is coupled with the governing equations. The solution procedure is described with the numerical results for a two-dimensional channel flow and a flow around a two-dimensional flat plate., 資料番号: NALSP0014029, レポート番号: NAL SP-14

An unmanned winged vehicle for space transportation called H-II Orbiting Plane (HOPE) are being studied by National Space Development Agency of JAPAN (NASDA). In the present paper, hypersonic computational fluid dynamics (CFD) analyses have been performed for HOPE 63 model proposed by NASDA. The effects of Reynolds Number, Mach number, angles of attack, and yaw angles are investigated in detail. In order to use CFD for more practical designing purposes, analyses of control surfaces and gas jet are also made. In addition, calculations of chemically nonequilibrium hypersonic flow are conducted for OREX (Orbiter Re-entry Experiment) model. The purposes of the present study are 1) to demonstrate the validity of the numerical code for aerothemodynamic heating, 2) to investigate the applicability of CFD for control problems, and 3) to develop reliable real gas CFD code. Numerical simulations have been done by using flux-split upwind Navier-Stokes cede., 資料番号: NALSP0014003, レポート番号: NAL SP-14

In the present paper, the Navier-Stokes code was used to compute the three-dimensional turbine stator flows. The computational results were compared with three experimental results about the linear cascade, the turbine bowed stator and the high-work turbine stator. The results show that the Navier-Stokes code has the significant potential to investigate the complicated viscous flow mechanism. In order to get more quantitative results, it is considered that the use of more rapid super-computer and the development of the turbulence model are needed., 資料番号: NALSP0014039, レポート番号: NAL SP-14

This paper deals with the pressure generated btween two flat disks in the fluid, one lower disk fixed and another upper disk moved perpendicular to the fixed lower one. Results obtained from the experiment are as follows :When the upper disk approaches the lower one, viscoelasticity of the fluid decreases the pressure below the pressure of corresponding Newtonian fluids, whereas in the case of separating the upper disk from the lower one, the pressure takes minus values of about - 3.5 × 10^5Pa and the magnitude is increased by the viscoelasticity of the fluid used. This minus pressure is raised to a vacuum pressure by the cavitation inception inferred, the vacuum pressure holds constant for a duration and finally the pressure abruptly increases by the cavity extinction which accompanies pressure vibrations of high frequencies. These experimental results are qualitatively explained using the assumption of squeezing flow and the constitutive equation of the second order fluid.

The vortices generating on a river bed were observed with 3 electro-magnetic flowmeters. Using obtained digital data, the distributions of velocity components, Reynolds stress, and energy spectrum were calculated. Distributions of diameter and velocity are represented in this paper. A conceputual model of river turbulence is proposed on the base of the results. Generating mechanism of horse-shoe vortices, sweeps, ejections, and boiles are explained based on the model.

This paper proposes a thrust bearing lubricated by a magnetic fluid under a magnetic field. The critical pressures of the bearing versus the magnitude of the magnetic flux densities have been investigated experimentally. It is clarified that the critical pressures of the proposed bearing are larger than those of the normal lubricant bearing under high speeds.

This paper discusses effects of viscous pumping in a magnetic fluid seal under a rotating load. The Reynolds equation was presented for the seal based on magnetic fluid mechanics, and the expressions for obtaining pressures in the seal, eccentricities of the rotating shaft due to the viscous pumping and seal pressures were given. Numerical Calculations were carried out for some sample problems, and the effect of magnetic flux densities on the pressure in the seal and the seal pressures were clarified.

This paper discribes an algorithm of timing analysis for nonlinear networks represented by piecewise-linear function. By using the proposed algorithm, it is not necessary to define time step size. Non-linear networks represented by piecewise-linear can be analyzed by linear-analysis method as linear networks, if region of any nonlinear element is not changed. If it is changed at t_b, we can not analyze the nonlinear circuit after t_b by linear-analysis method. In this case, we get V(t_b) which is the node voltage at t_b. And we can analyze the circuit after t_b using the new linear equation and the initial value V(t_b).

This paper presents the experimental analysis of power augmentation effects of horizontal axis wind turbine using a tip vane. The flow visualization method is used to analyze the augmentation phenomenon. The flow around a tip vane, tip vortex and flow patterns on the blade surface are visualized. The following results are described. (1) Strength of tip vortex, induced drag and turbulence on the blade tip can be diminished by the tip vane. (2) A tip vane can generate the diffuser effect.