Investigation on compact design of rocket pump impeller and diffuser by using inverse deign was presented. Two compact sizing, 95% and 90% of original design based on impeller and diffuser exit radius were investigated in this study. The performances and internal flow fields in the inverse designed impellers and diffusers were evaluated by Computational Fluid Dynamics (CFD) technique. The CFD results show the flow non-uniformity at the impeller exit tends to be increased from increased blade loading of compact design. The compact sizing of 90% of original design shows large penalty in performance at the 94% design flow by diffuser stall. The compact sizing 95% of original design showed a small performance penalty to original design in the range of 94% to 106% design flow rate, however impeller performance improvement compatible to the original design was expected by adopting wider impeller exit width.

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Recently, it had been clarified that the flow field in an axial flow compressor rotor at rotating stall consists of a tornado-type separation vortex linking from the blade suction surface to the casing wall. In the present work, unsteady three dimensional flow behavior of separated flow at rotating stall has been investigated by large-scale unsteady RANS (Reynolds-averaged Navier-Stokes) simulations. The results show clearly the rotating stall propagation process, which is different from the guess in the past experimental work that a similar separation vortex must revolve stably in the rotor. It has been found that the separation vortex causes a leading edge separation at following blade due to the large blockage effect and the new separation vortex propagates at the blade passage again.

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One method to predict the axial thrust is to use the relationship between the total head and axial thrust, where the axial thrust is supposed to be in proportion with the total head. But such method has insufficient prediction accuracy because it can not properly predict the circumferential velocity according to the direction of the leakage. We developed a numerical simulation method to predict the circumferential velocity properly. First, the numerical domain of the fluid part, including the impeller and vaned diffuser, was calculated. Second, that of the rear part located on the back side of the hub was calculated. The leakage in the rear part is usually about 5% less than the discharge in the fluid part, therefore the influence from the rear part to the fluid part is neglected. Three pump types were calculated and we could predict the maximum axial thrust with a high accuracy of ±6%.

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In the present study, we focused on the length of the tip cavitation as a parameter of cavitation in order to investigate the thermodynamic effect on a cavitating inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect. Sub-synchronous rotating cavitation appeared both in liquid nitrogen and in cold water. To the contrary, cavitation surge occurred only in cold water at lower cavitation numbers. It was inferred that the thermodynamic effect decreases mass flow gain factor M at lower cavitation numbers when the cavity length develops over the throat, and that its effect suppresses the cavitation surge in liquid nitrogen.

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In the present study, we focused on the length of the tip cavitation as a parameter of cavitation in order to investigate the thermodynamic effect on a cavitating inducer. Comparison of the tip cavity length in liquid nitrogen (76K and 80K) with that in cold water (296K) allowed us to estimate the strength of the thermodynamic effect. Sub-synchronous rotating cavitation appeared both in liquid nitrogen and in cold water. To the contrary, cavitation surge occurred only in cold water at lower cavitation numbers. It was inferred that the thermodynamic effect decreases mass flow gain factor M at lower cavitation numbers when the cavity length develops over the throat, and that its effect suppresses the cavitation surge in liquid nitrogen.

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A flow model of two-phase media composed of a liquid and spherical gas bubbles is developed for computing high-speed cavitation flows. State equations of liquid and gas phases are employed to relate density with pressure, and a set of governing equations are solved by the CIP-CUP method. Cavitation inception is then evaluated by a gas volume fraction according to a bubble radius in a local field. As an example of computation, an orifice nozzle flow is treated, and the reliability of the computation is estimated by comparison with experimental data.

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Vapor production through cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity. This is called thermodynamic/thermal effect of cavitation and leads to the good suction performance of cryogenic turbopumps. We have already established the simple analysis of partially cavitating flow with the thermodynamic effect, where the latent heat extraction and heat transfer between the cavity and the ambient fluid are taken into account. In the present study, we carry out the unsteady analysis to obtain the unsteady cavitation characteristics such as cavitation compliance and mass flow gain factor, which are known to be important parameters for cavitation instabilities appearing in cavitating inducers. It is found that the thermodynamic effect on the cavitation characteristics becomes significant when the cavity becomes longer and the trailing edge approaches the throat of the blade passage.

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The unsteady cavitating flow in a turbopump inducer has been calculated using an accurate three-dimensional detached eddy simulation (DES) code, which took into account the cavitating phenomena. The three-dimensional code is based on the numerical method for compressible flow using low Mach number flow approximation and a cavitation model. Qualitative agreement between our computational result and experimental data was satisfactory. The magnitude of the fluctuation in cavity volume increased as the cavities extend and close to the throat of the blade passage. The effect of the tip-gap on the cavity volume was shown; the time-averaged volume of cavities for the inducer with the tip-gap was about five times larger than that for the inducer without the tip-gap at an operating condition. Vorticity generation in cavities due to baroclinic torque was found. Multiple blade passages calculations are under way to find unsteady phenomena such as rotating cavitation.

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[in Japanese]

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We have treated with a dilute dispersion composed of ferromagnetic rodlike particles with a magnetic moment normal to the particle axis, such as hematites, to investigate the influences of the magnetic field strength, shear rate, and random forces on the orientational distribution of rodlike particles and also transport coefficients such as viscosity and diffusion coefficient.

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[in Japanese]

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We have investigated the validity of the application of the dissipative particle dynamics (DPD) method to ferromagnetic colloidal dispersions by conducting DPD simulations for a two-dimensional system. Firstly, the interaction between dissipative and magnetic particles has been idealized as some model potentials, and DPD simulations have been carried out using such model potentials for a two magnetic particle system. In these simulations, we have concentrated our attention on the collision time for the two particles approaching each other and touching from an initially separated position, and such collision time has been evaluated for various cases of the mass and diameter of dissipative particles and the model parameters, which are included in defining the equation of motion of dissipative particles. Next, we have treated a multi-particle system of magnetic particles, and have evaluated particle aggregates and the pair correlation function along an applied magnetic field direction. Such characteristics of aggregate structures have been compared with the results of Monte Carlo and Brownian d ynamics simulations in order to clarify the validity of the application of the DPD method to particle dispersion systems.

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In order to investigate the relation between flow structure and free sphere's motion in the divergent channel expanding upwards, observation of the sphere's motion and PIV analysis of the flow were carried out. The sphere motion could be classified into two categories; pattern (a), the sphere lifts toward the flow direction with rotation; and pattern (b), the sphere lifts with rotation also revolution along the channel wall. Pattern (a) appears when the Reynolds number of the flow around the sphere is larger than a certain value given by the sphere weight and size, and vice versa. A vortex ring is generated in the sphere wake and it horizontally stays in the case of Pattern (a). The vortex ring, however, cants to the sphere side and revolves with the sphere in the case of Pattern (b).

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In this study, experimental and numerical investigations were performed to obtain the fluid flow characteristics of gaseous flow in micro-tube with 180° bends. Especially, attention was put on the influence of compressibility in micro-tube. Experiments were performed on micro-tube with bend having diameter of 75, 100, 150μm with Reynolds number which range from 100 to 500. Furthermore, numerical investigations to obtain detailed effects in bend in micro-tube were performed, and the influences exerted by compressibility and bend were investigated.

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We experimentally studied the behavior of a single bubble in superpurified water. We developed the apparatus that can maintain the purity of water during the experiment. The apparatus is equipped with the measurement system for the resistance and TOC value of water so that we can quantitatively evaluate the purity of water. We investigated the critical Reynolds number over which the rising motion of bubble changed from rectangular to zigzag or spiral. We found out the critical Reynolds number was 660 for a bubble in superpurified water. We also compared the experimental results for terminal rise velocity and drag coefficient with the theoretical value for ellipsoidal bubble obtained in the limit of potential flow theory. For small bubbles, experimental values of the terminal velocity and drag coefficient were in good agreement with theoretical ones. For large bubbles, however, experimental values and theoretical ones had the relative deviation of about 8% in the terminal velocity and drag coefficient. This is because the bubble shape shows a deviation from fore-aft symmetry.

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[in Japanese]

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A model for an irregularly indented rough surface has been proposed by the authors in which tall peaks are picked up and represented by hemispheres having equal volume with each concerned peak. In practical application, drag of hemispheres are substituted by plane shear stress on a flat plate. This simplified model surface is used to simulate flow over the original rough surface. The model requires drag of a hemisphere on a flat plate. In this work, appropriate formula for the drag which is simple and acceptably accurate in balance with the compactness of the model, is deduced by numerical simulations. Channel flows having periodically arranged hemispheres on both plates are simulated using two-equation turbulence model. Obtained drag form is confirmed to compare reasonably with those realized by hemispheres of different size and in different situation, in a flow equipped with the model rough surface. The form is applied also to pipe flows having periodic hemispheres on the wall and is found to reproduce measured friction. Although the proposed idea must be examined more carefully and improved in details, promising step has been set up to make proposed model an important method in practical application.

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Quasi-periodic nature of large-scale motions in the outer region of turbulent boundary layer is considered. A simple model calculation using a 2D discrete vortex method is performed on the presumption that the mechanism responsible to the quasi-periodicity might be an inviscid, varicose-mode instability of a symmetrical vorticity field which consists of a boundary layer flow under consideration and its mirror image with respect to the wall. The preferred wavelength determined from the model flow is roughly comparable with but non-negligibly longer than the corresponding wavelength observed by Taneda(1982) in his flow visualization experiments.

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Heat transfer mechanism across the wind-driven air-water interface was investigated through laboratory experiments in a wind-wave tank. Heat transfer coefficient on the water side was measured through evaporation experiments and the distribution of water surface temperature was measured using an infrared imaging technique. The results show that the increasing behavior of heat transfer coefficient on the water side against wind-speed becomes gentle and tends to level off in the middle wind-speed region. It indicates that the traditional assumption based on the proportionality between heat transfer coefficient on the air side and wind-speed is not correct. In contrast, heat transfer coefficient on the water side increases approximately in proportion to the frequency of the appearance of surface renewal eddies for whole wind-speed region. This result suggests that heat transfer across a wind-driven air-water interface is dominated by the surface renewal motion near the air-water interface.

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Experiments have been performed for a turbulent channel flow obstructed by two parallel triangular cylinders in tandem arrangement. The triangular cylinder of two kinds of the angle is used. The first and second triangular cylinder is same. The clearance between the wall and the triangular cylinder is changed in three steps. The distance between two triangular cylinders is varied from 80mm to 300mm. The total performance between pressure drop and heat transfer are estimated under the condition of an equal pumping power. When the angle of triangular cylinder is 45 degrees and the clearance is small (S=1mm), the highest performance is obtained.

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Large scale structures in outer layer of wall-bounded shear flows, that is, a zero-pressure-gradient boundary layer and plane wall jet above flat plates, were investigated experimentally. Our objective is to clarify mean properties of the large scale structures in the intermittent region. Measurements were made by using I-type and X-type hot-wire probes, and an I-type rake probe with 16 hot wires along the spanwise direction. Turbulent/non-turbulent intermittency factor was calculated, and then from these distributions, a center position and width of the intermittent region were estimated. And also, RMS values of the streamwise velocity fluctuation at the center position were defined as a velocity scale. Wavenumber spectra were transformed from the measured velocity data by the rake probe, and spanwise length scales were estimated from these spectra. Reynolds number dependencies of scales of length and velocity were examined.

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To propose an effective method of jet mixing in low Reynolds number, two and four inclined multiple jets are examined using Direct Numerical Simulation (DNS). The spatial descritization is performed by hybrid scheme, in which sixth order compact scheme in streamwise direction and fourier series in cross section are adopted. In case of two jets, large-scale vortex structures which are the shape of concentric circle formed around collision point and then break down at downstream. However, in case of four jets, large-scale vortex structures does not formed, a large number of minute vortex occure. From the mixing property which was estimated by using entropy analysis, we found that two jets was more mixed than single jet or four jets.

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A jet into a counter flowing uniform stream is very important to clear flow in a combustor. There are many researches in round jet and two-dimensional jet. In two-dimensional jet into a counter flowing uniform stream, we grouped into three classes, attached flow, puffing flow and flittering flow. An annular jet has both nature of a round jet and two-dimensional jet. So the annular jet into the counter flowing uniform streams has wide applications in industrial world. In this paper, the flow fields are classified by means of visualization by schlieren method. And we discuss the characteristics of the flow fields.

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The determination procedure of the vortex core region in the vortex ring attached to the shear layer in a pulatile jet flow was studied experimentally with PIV under the condition of a distance to the wall L^* =1.15 and 2.26 to measure the circulation of vortex ring. It was obtained that the distribution of the vorticity ζ^* and the circumferential velocity V_0 around the vortex center were compared with the Oseen vortex solution, and both were in good agreement with the Oseen vortex independent of the L^*. The threshold level of the vorticity defined at the maximum point of the V_0 to decide the vortex core region in the vortex ring. The vortex core region, similar to the forced vortex flow in the Rankine-Vortex, is defined as the region where the vorticity is higher than the threshold level. The circulation of the vortex ring is then estimated by the integrated the vorticity in the vortex core region.

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In this study, secondary film flow is built on the outside of axisymmetric jet. And it is driven by the acoustic excitation for active jet control. Furthermore, the velocity ratios of mainstream and film flow and acoustic Strouhal number were changed. It is analyzed the measurement and analysis velocity distributions by hot wire anemometry to examine of controlled jet structure. From the velocity distribution map and a turbulence strength distribution map of a jet, secondary film flow had a rectification effect in a radial direction, and Jet by Acoustically driven had a rectification that there was a diffusion effect in a flow direction. We confirmed the plural modes which coexisted in Jet by spectrum analysis. Jet diffusion is restrained plural vortexes interfere it in the case of VR=0.5, and to disturb growth of a vortex. In the case of VR=1.0, diffusioned increases so that a vortex spreads while two characteristic modes are resonant.

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Active control is applied on a circular jet using secondary film flow, with and without acoustic excitation. The velocity ratio of the film flow to the main stream and/or acoustic excitation frequency is changed. This active control method is applied on a circular jet buoyant jet (Carbon dioxide or Helium gas). The jet structure is visualized with laser light sheet in the plane including jet axis. It is described qualitatively the process of vortex ring growth and outbreak that it is generated in the shear layer of jet.

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In this paper, an experimental study is performed to reveal the effects of a nozzle exit shape on vortex formations in the pulsating jet. A pulsed hydrogen bubble technique is used to observe the vortex formation from rectangular cross section nozzle of an aspect ratio (AR) of 31.25. The pulsating jet is generated by superimposing large amplitude and low frequency pulsation on the steady flow. Obtained results are as follows: The vortex pairs are formed due to pulsation at the interval of the pulsation period in the both minor and major plane. The flow patterns are affected by shape of the nozzle. The variation of the distance between a vortex pair in the minor plane of the high AR nozzle is smaller than that of the low AR nozzle. The vortex pair is generated from the low AR nozzle moves faster downstream than that from high AR nozzle.

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A basic study of flow controls using jets was conducted to reduce an unsteady aerodynamic force acting on a train in tunnels. We installed air jet devices around a model car in the wind tunnel and measured pressure fluctuations on the side of the vehicle. The results shows a) jets allow to reduce pressure fluctuations, b) it is effective to jet air horizontally at the lower side of the car facing the tunnel wall, and c) the reduction rate of the pressure fluctuations may be relate to the square of the rate of the jet speed to the train speed.

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The effects of rainfall on mass transfer across the air-water interface were investigated through laboratory experiments in a turbulent open-channel flow. The CO_2 absorption rate due to raindrops impinging on the free surface was measured by a soap-film flow meter. The mass transfer coefficient on the liquid side, k_L, is well correlated with the mean vertical momentum flux of rainfall, MF, but it is not well correlated with the mean kinetic energy flux of rainfall, KEF, which has been proposed as the best parameter for correlating k_L in the previous studies. The CO_2 absorption mechanism is clarified by the visualization of velocity and CO_2 concentration fields by means of PIV and LIF.

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