In centrifugal turbomachines, guide vanes, namely circular cascades, are installed to change the circulation of the radially outward and/or inward flow in the fixed channel. There are many studies on guide vanes for the outward flow, such as diffusers. On the contrary, studies on guide vanes for the inward flow are limited, so it is desirable to study this aspect further. From such a viewpoint, this review presents the recent progress of research in Japan on circular cascades for the inward flow. Circular cascades include wicket gates of water turbines, return vanes of multistage centrifugal turbomachines and diffuser vanes of mixed-flow pumps. The cascades installed in the machines for high head or high pressure are composed of thick vanes with a small aspect ratio. The most important problem in these cases is a flow separation on the vane surface, this separation complicates Kutta's condition for the cascade theory. Moreover, a secondary flow also considerably affects the through-flow. These are all considered as main problems in this review.

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Recently, engineering problems associated with two-phase flows in turbomachinery have become increasingly important in relation to the safety analysis of nuclear reactors or the usage of low quality energy resources; the research on this subject has been promoted. It is a really knotty problem caused by the multiform flow patterns as well as the variety of its applications. However, the mechanics in two-phase machines may involve similar phenomena. In this paper, developments of the research of air-water mixtures in turbomachinery well be briefly reviewed, and the mechanics of two-phase flows in rotating flow fields and the prediction methods of the performance of turbomachinery based on some analytical models are discussed.

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Hot wire measurements of three fluctuating velocity components u', v', and w' have been carried out in a pulsatile pipe flow accompanied by relaminarization. Conditional sampling was made in addition to the evaluation of turbulence intensities and Reynolds shear stresses. The onset of relaminarization and the following retransition to turbulent flow were judged from these experimental results. Turbulent motions were classified into four distinct categories. The contributions of sweep and outward interaction to the Reynolds shear stress and the turbulence energy are dominant in the earliest stage of the accelerating period where the ordered motions called bursting gradually cease due to a combined effect of viscosity and acceleration. Meanwhile, the ejection and the wallward interaction play an important role when the production of turbulence reoccurs in the last stage of the accelerating period. After the turbulence generated near the wall reaches the pipe center, the ordered motions become the same as those in steady pipe flow.

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This study aims to clarify the structure and dynamic behavior of the linear system which describes the small perturbation of a laminar pipe flow. In the preceding paper, the eigenvalue problem was formulated in a Hilbert space based on the spectrum theory. A numerical method for calculating the eigenvalues was proposed together with a measure of accuracy. Applying the proposed method in this paper, we discuss the distribution of eigenvalues and the mode of perturbations for the Poiseuille pipe flow. The wave perturbations for various azimuthal and axial wave numbers are investigated with a fixed Reynolds number. It is shown that the distribution of eigenvalues in a complex phase velocity plane assumes a tree-like shape. The mode of perturbations is divided into three classes : slow, fast and mean modes by the axial phase velocity ; or wall, center and neutral modes by the radial distribution of the magnitude of the eigenfunction. For each mode, the location of the corresponding eigenvalue in the complex phase velocity plane is clarified, and the dependence of the eigenvalue on the original linear dynamic system is also clarified by computer calculations.

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An experimental study is presented which deals with the deflection and reattachment of an axisymmetric radial turbulent wall jet discharged from a cylindrical nozzle onto an adjacent disk plate, in the presence of a lateral control flow. Mean and turbulent velocities were measured with a hot-wire anemometer, while static pressure distributions along the wall surface and across the jet flow were measured by means of static pressure probes. The effects of various control flow rates (ratio of the control flow rate to the main jet flow rate) on the jet flow properties in the region before a reattachment point were investigated. The mean negative pressure in a recirculating flow region, the position of the reattachment to the wall surface, the changes of the maximum jet center velocity, the jet half width, and the turbulence intensities at the velocity maxima depend mainly on the control flow rate.

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Momentum integral equations for turbulent flow through curved pipes have been set up in consideration of a viscoelasticity of dilute polymer solutions and solved approximately. The resulting coefficient of pipe friction has been compared with experimental results and presented in a form suitable for engineering use. In addition, the boundary layer thickness, velocity distribution of the secondary flow and pressure difference between the inner and outer sides have been described.

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A cascade flow, which is the most fundamental phenomenon in turbo-machinery, is calculated numerically under bubbly two-phase flow conditions. The governing equations for two-phase flow are formulated with emphasis on local density distribution and sound velocity distribution caused by slippage between the bubbles and the surrounding liquid. The numerical results reveal some characteristics of the bubbly blade to blade flow. The flow has the characteristics of a compressible flow ; it is compressible flow, of which pressure and Mach number are widely distributed. The void fraction around the stagnation point of the blade decreases due to the slippage driven by the pressure gradient, and the flow around the stagnation point becomes similar to an incompressible flow. The pressure recovery on the blade surface decreases due to accumulated voids in the low pressure part on the blade. The relaxation zone of the shock wave becomes thicker due to the slippage.

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An experimental study was conducted for revealing unsteady aerodynamic characteristics of oscillating cascades with tip clearance. To obtain aerodynamic forces acting on blades, the surface pressure was measured in both the chordwise and spanwise directions. To evaluate the aerodynamic forces due to oscillations of arbitrary interblade phase angle, the method of influence coefficients was adopted. Tip clearances were changed from 0.056% to 2.8% of the blade span. The aerodynamic blade loading was also changed. Results show that the tip clearance has a strong influence on the distribution of unsteady aerodynamic forces along the blade span : when tip clearance exists, aerodynamic damping forces decrease considerably over a large portion of the blade span. However, when steady aerodynamic loading acts on the blades, the influence of tip clearance is suppressed. The tip vortex increases the absolute value of the unsteady aerodynamic force in the region near the blade tip.

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This study investigates the possibility of significantly improving the performance or sharply bent S-draft tubes by a conventional, but comparatively simple method ; by adjusting the divergent angle of the conical straight portion at the upstream part of the draft tube. This paper describes this method, as well as a phenomenon associated with secondary flow in sharply bent S-draft tube in which the flow changes its direction intermittently. This phenomenon is important because the use of sharply bent S-draft tubes is preferred in some cases due to civil engineering requirements for turbine installation. Therefore, this report attempts to clarify the phenomenon in detail.

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A Wells turbine operating under an irregular wave condition has been analyzed theoretically. It is shown that the turbine performance depends on a unique parameter, which includes characteristic parameters of irregular waves, turbine speed and dimensions of the turbine and air chamber. In order to obtain the optimum value of this parameter, a model test has been performed in a computer-controlled wind tunnel, which can simulate any kind of oscillating flows based on spectra of irregular waves. From this value, a set of optimum dimensions of the Wells turbine system can be determined. Furthermore, starting and running characteristics of the Wells turbine have been obtained by a computer simulation and compared with the experimental results. It is possible to predict the optimum value of the parameter and behavior of output coefficient by computer simulation.

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A thermal anemometer using a transistor as a sensor has been constructed and tested. The sensor is intermittently heated electrically so that its temperature goes up and down periodically between two prescribed limits. Since the time required for the temperature to rise to the upper limit depends on the speed of the surrounding fluid, we can use the time detected to determine the velocity of the fluid. The anemometer works under small temperature differences between the sensor and the fluid. It is highly durable, and shows a high sensitivity to wide range of fluid speeds.

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The relation between thermal conductivities of superconductors (Nb₃Sn, V₃Ga) and temperature was studied. We used the steady-state comparative-plate method which is suitable for measuring the thermal conductivities of superconductors at low temperatures. For our experiment, a reference metal of lead was placed in series with a superconductor specimen. This method has the advantages of a simpler setup for both the specimen and the equipment. The temperature was measured with AuFe_Cr thermocouples embedded in copper grooves on the superconductor specimen. The thermal conductivities of the superconductors gave obviously lower values in the region below the transition temperatures as compared with the thermal conductivities of normal conductors. The nondimensional thermal conductivities, λ/λ_c, normalized by the thermal conductivities at the transition temperatures of Nb₃Sn and V₃Ga for a nondimensional temperature, T/T_c, were found to be given by a generalized curve (identical to a theoretical curve obtained using a theory developed in the present study based on the B. R. T. theory).

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numerical predictions were compared with the experiments of turbulent heat transfer in a pipe where the swirl flow is induced by the pipe wall rotating around the pipe axis. The heat transfer deterioration due to the swirl observed in the experiments was well predicted by the calculations applying the stress/flux equation model. The laminarization phenomena which indicate the laminar-like axial velocity profile due to the swirl were also predicted. It was revealed that the heat transfer deterioration and the laminarization phenomena are caused by the additional production terms including tangential velocity component due to swirl in transport equations of radial turbulent fluxes of momentum and heat. The additional production terms have significant effects of suppression on the turbulent transport of heat and momentum.

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Experimental studies on the fluid flow and heat transfer around a circular cylinder with vortex generators were carried out in the range 1.3×10⁴<__=Re<__=5.2×10⁴. Depending on the height of the vortex generator and the Reynolds number, four flow patterns were found to result from the transition of the boundary layer and the flow separation. The local and average heat transfer coefficients on the rear surface vary with changes in the drag coefficient, the rms fluctuating pressure and the reciprocal of the Strouhal number. The heat transfer coefficients at the rear stagnation point, h_r, for the four patterns are related to the Strouhal number as Nu_r/Re^2/3=0.018/S^1.4, within an error of 10%, and also to the rms fluctuating pressure, Δp_r, at the rear stagnation point as : h_r∝Δp_r^0.31.

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A theoretical model of film condensation on a horizontal low-finned tube developed in a previous work is generalized. The new model includes the effects of condensate flow and heat transfer on the fin root tube surface in the unflooded region of the tube, and the wall temperature variation between the fin root and the fin root tube surface. The expression for the flooding angle is also extended to include the case of relatively large fin spacing as compared with the fin height. It is shown that the new model can predict the average heat transfer coefficient satisfactorily over a wide range of fin spacings. An agreement of within ±20% is found between the predictions of the present model and most of the available experimental data covering 12 fluids and 31 tubes.

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The purpose of this study is to obtain basic information for the design of a convergent-divergent nozzle for flashing expansion of initially subcooled water. The conical-type nozzles had a sharp-edged throat of 3.5 mm diameter. Nozzles with different divergent angles and different exit stream-expansion ratios were tested. Initially subcooled water samples at an inlet pressure of 0.47 MPa and inlet temperatures of 409.7 to 421.5 K (inlet subcoolings of 13 to 1.2 K) were used in the range of nozzle back pressures of 10 to 160 kPa. As a result, (1) The values of the thrust coefficient are discussed in relation to the subcooling, back pressure, nozzle divergent angle, and exit stream-expansion ratio ; (2) A method to determine the optimum exit stream-expansion ratio for a given pressure ratio is proposed ; and (3) The relationship between the critical mass flow rate and the critical pressure ratio is discussed based on the experiments.

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An experimental and theoretical study of Leidenfrost film boiling when a volatile liquid droplet is released onto a hot liquid surface is presented. Photographic studies are first made with respect to the evaporation configurations. The evaporation-time curve for a variety of liquid-liquid combinations is measured and the Leidenfrost temperature is proved to be correlated by the interface temperature and the superheat limit of the volatile liquid. A heat- and mass-transfer model of liquid-liquid Leidenfrost film boiling is proposed and formulated theoretically. The calculated results of the theory are compared with the experimental radius-time data, where the radius decreases linearly with the lapse of time, except for the final stage of evaporation, and a good agreement between them is obtained. Further, the effects of physical properties are evaluted on the basis of the theoretical calculations.

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A new concept of the enhancement of forced-convection heat transfer effective in the range of Reynolds numbers lower than 3 000 is presented. The new surface has many small holes and is bent to form a trapezoid. The phase of each adjacent surface is changed by half a period, and therefore a heat exchanger constructed with these perforated surfaces alternately has enlargement and contraction sections along the flow passages. The performance of the new heat exchanger employing this enhancement technique is studied experimentally. It is shown that the mechanism of the heat-transfer enhancement is mainly due to the secondary flow induced by the suction and injection through the perforations. The heat-transfer coefficient of the new heat exchanger increases by about three times that of a parallel-plate heat exchanger at the same Reynolds number.

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The operating performance of a large-scale metal hydride heat pump, whose design is optimized by numerical simulation, has been investigated. The heat exchanger in the heat pump, which is of a shell and tube type with copper fin tubes to enhance heat flux through the metal powder, contains two different metal hydrides in one shell; each hydride is completely separated by a center plate. The purpose of the present investigation is to demonstrate the performance of the heat pump, which has been numerically predicted, and to ascertain the optimum operating conditions. As a result, a heat output of approximately 174 kW in the heat upgrading cycle time of around 10 minutes.

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It is widely known that NO_x emission from an engine plays an important role in the formation of varnish and sludge in engine oil. Therefore, the authors measured the concentrations of nitric and nitrous acid ions in lubricating oil and analyzed the process through which NO_x mixes into the lubricating oil. The latter was found to occur through oil film on the cylinder wall and through crankcase gas, the amount being proportional to the NO_x concentration of nitrous acid ions when the engine temperature drops results in the condensation of water vapor contained in crankcase gas.

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A numerical analysis is presented for a CO chemical laser, which utilizes the supersonic mixing of dissociated products of CS₂ diluted in Ar with O₂. It is assumed that the flow is quasi-one-dimensional, and that nozzle flows undergo instantaneous mixing at nozzle exits. The constant gain method is applied to estimate the laser power. The present results show that the rate of formation of CO molecule is scarecely reduced by lasing, although the temperature rise in the reacting flow field is suppressed due to the conversion of chemical energy into laser energy. It is also shown that about 19.5 kW laser power can be extracted from a supersonic flow CO chemical laser, in which the cross-sectional area of the flow field is 50 mm × 450 mm.

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