Showing papers in "JSME international journal. Series 2, Fluids engineering, heat transfer, power, combustion, thermophysical properties in 1991"

SEM Observation of the Vibratory Cavitation-Fracture Mode during the Incubation Period and the Small Roughness Effect

Abstract: Vibratory-erosion tests on a typical ductile material, 304 stainless steel, were carried out under a specified condition of uniform cavitation-nuclei-size distribution. We systematically investigated the behavior of the fracture mode on a smooth surface one figure smaller in roughness than the ASTM recommended value, as well as small roughness effects in the development and/or propagation of cracks and particle fall-off, in the second stage of the incubation period, by means of a scanning electron microscope. It is clear that the mode is fatigue and ductile fracture, and also that small roughness plays an important role in development and/or propagation of the cracks and also in microscopic removals, which shorten the incubation period.

Absorption of Water Vapor into a Wavy Film of an Aqueous Solution of LiBr

Abstract: A model of laminar flow with a smooth surface was proposed for the prediction of the absorption rate of water vapor into an absorbent film flowing down a vertical plate simulating a cooling pipe in the absorber of an absorption chiller. However, the falling fi1m begins to show a wavy surface as the film Reynolds number exceeds 20. In this paper, the process is numerically analyzed by assuming sinusoidal wave motion over the falling film. The velocity profile inside the film is determined following Kapitza's analysis. The wave phase velocity and the wavelength are determined from Pierson's equations which are derived from the stability analysis. The wave amplitude is assumed to be 30% of average film thickness. The results are compared with those of a laminar flow with a smooth surface. It is found that the absorption rates increased by a factor of more than 1.7-2.4 over the film Reynolds number range of 20-100.

Experimental studies on a preferable blade profile for high efficiency and the blade characteristics of Darrieus-type cross-flow water turbines

Abstract: Fluid forces and moment acting on a blade of the Darrieus-type runner were measured in addition to the blade performance The characteristics for various type of blades were evaluated from the measured data with theoretical considerations in an inviscid flow Some features of those characteristics, including the dynamic effects caused by an unsteady relative flow around the Darrieus-blade, are shown in the present paper For high efficiency, a noncambered thin blade with relatively long chord length is recommended Its characteristics are high lift slope, high lift at zero angle of attack and relatively low drag in a wide no-stall region of attack angles It should also be set tangent to the runner pitch-circle at the 50% chord point of the blade

A Numerical Method of Flow through a Cross-Flow Runner

Abstract: The flow inside a cross-flow runner is analyzed two dimensionally. The unsteady flow along streamlines in the relative systems of the runner is calculated numerically and the flow along the runner periphery is investigated. Additionally, calculated results are compared with experimental data

Aerodynamic Loads on a Stationary Savonius Rotor

Abstract: The discrete vortex method was used to provide detailed information on the flowfield and starting torque on a stationary Savonius rotor. The rotor position normal to the wind was selected to examine the local flow properties on and around its buckets

Measurement of Cylinder Bore Deformation by means of a Turning Piston with a Gap Sensor during Engine Operation

Abstract: Measurements of cylinder bore radial deformation were made along the peripheral direction during actual engine operation. A piston, whose upper part was capable of turning, was installed on the pin boss and was slowly turned from an outside power source by means of a gear train. A heatproof inductance-type gap sensor was embedded on the second land surface. When the engine was under steady-state operation, the piston position at any crank angle was fixed every cycle, not only axially but also inside the corresponding cylinder cross section. As a result, the cylinder bore deformation was continuously measured by one sensor along its entire periphery at one desired axial piston position. One of the important measurement results was that the compound effect of head bolt force and thermal stress had a significant influence on the bore deformation.

The Permeability of Screen Wicks

Abstract: An experimental study was performed on the permeability of screen wicks using water. A1so, an equation for the wick porosity influencing the permeability was proposed based on a model of the screen geometry. In the present experiment, screen mesh size, number of screen layers, packing condition of the screen and flow rate were changed. For the friction factor, a correlation Cf=A/Re was obtained ; here the coefficient A was related to the packing number ω defined by the ratio of n-layer thickness to n-times the single layer thickness of the screen. Consequently, it was found that the permeability of the screen wicks could be predicted considerably well from the expression presented in this study and became steeply large with the increase in the packing number ω, which showed the degree of hold-down pressure for screen wicks.

Predicting the effects of surface suction and blowing on the strouhal frequencies in vortex shedding

Abstract: Through the use of scaling arguments, a simple model describing the boundary layer behavior during vortex shedding is proposed. The main focus of the model, which is based on the assumption that the viscous diffusion length is directly proportional to the boundary layer thickness, is set towards predicting the salient features, but not the details, of the periodic flow. Promising results have been achieved upon applying the model to the classical problem of vortex shedding over a solid circular cylinder

Construction of a Flow-Simulating Method with Finite Volume Based on a Voronoi Diagram

Abstract: In flow simulations performed with the finite difference method or the finite volume method, it is a serious limitation that the calculating points must be ordered on the coordinates. Using the Voronoi diagram for the cell division of the finite volume method creates a new discretization form which permits an arbitrary distribution of points

Experimental and Theoretical Investigations on Heat Transfer of Strongly Heated Turbulent Gas Flow in an Annular Duct

Abstract: Heat transfer experiments have been conducted on strongly heated gas flow in an annular duct. Special attention is paid to the laminar-turbulent transitional region. The results show that laminarization was not observed within the range of the experiments although this phenomenon took place in a heated circular pipe when other conditions were the same. Above a certain heat flux, heat transfer coefficient in the downstream tends to follow a new correlation: Nus=0.071Reb0.6Prb0.4 which is independent of the heat flux. Numerical analyses are made using 3 types of turbulence models: k-kL-(uv)^^-, k-e-(uv)^^- and k-e models. The calculations were compared with the measurements and better agreement was obtained for the k-kL-(uv)^^- model.

Mixture strength measurements in the combustion chamber of si engine via rayleigh scattering (2nd report, results for liquid fuel injection)

Abstract: An experimental study was made of the fundamental aspect of the mixture formation in the combustion chamber of an automotive spark ignition engine with multipoint fuel injection. The mixture formation process during the intake stroke of an engine was simulated by the intermittent injection of gasoline or Freon-113 into the steady flow of dust-free dry air through an intake port. The time histories of the vapor concentration at several locations in the transparent combustion cylinder were determined with the application of the laser Rayleigh scattering. The measured results were expressed in terms of the peak vapor concentration at the location of interest, the period of time between the initiation of the liquid fuel injection and vapor arrival, and the duration for the vapor to be observed over a wide range of injection pressures, injection durations, intake valve temperatures, intake valve lifts and intake air flow rates

A Study on the Structure of Premixed Turbulent Propagating Flames : An Investigation and Application of the Flame Plasma Potential Signal

Abstract: A method using a passive electrostatic probe to detect a flame by its plasma potential signal has been developed. The spatial resolution of the probe in this method is shown to be significantly improved over that of the conventional electrostatic probe. The plasma potential signals obtained by this method from premixed turbulent propagating flames show one to six spikes in each signal; each spike is considered to be a flamelet in the flame zone. On the basis of this consideration, the propagating speed, the thickness of the flame zone, the number of flamelets in the zone, the separation distance between two adjacent flamelets, etc., of the flame, were obtained