Showing papers in "JSME international journal. Series 2, Fluids engineering, heat transfer, power, combustion, thermophysical properties in 1990"

A Numerical Analysis of Flow around Rectangular Cylinders

Abstract: By a finite difference method, flows around cylinders with rectangular cross sections of various width-to-height ratios of 0.4 to 8 have been computed in the range of Reynolds numbers of l00 to 1200. We have successfully simulated some interesting phenomena whereby flow around the cylinder of the B/H ratio of 2 changes to a fully separated flow at a Reynolds number of 800, while for the cylinder of the B/H ratio of 2.8, a fully separated flow changes to an alternate reattachment one at a Reynolds number of 1200 with the lapse of time, two components with different Strouhal frequencies appear in a flow field around the cylinder of the B/H ratio of 6 at a Reynolds number of 800, and the flow pattern critically changes when the B/H ratio is 2.8 and 6 at Reynolds numbers of 500 to 1200. It is clarified by a numerical simulation that the component with a high Strouhal frequency is induced by vortices separated from the trailing edges and that the low Strouhal component is due to the oscillation of flow over the side walls accompanied by a movement of separation bubbles. Finally, the computed results of flow patterns, base pressure, drag force and Strouhal number show a good agreement with the experiments.

Numerical Analysis on Two-Dimensional Flow and Heat Transfer of Louvered Fins Using Overlaid Grids

Abstract: Using an overlaid grids method, finite difference analysis have been made on two-dimensional flow and heat transfer characteristics of louvered fins which comprise automotive heat exchangers used in the forced convection regime at low Reynolds number. In this method the physical domain is subdivided into some regions which can adapt easily to Cartesian grids. The maximum total number of the grid points allocated non-uniformly in the respective regions is about 100000. Communication between the grids is accomplished by linear interpolation of the dependent variables at grid boundaries. It took 3060 minutes of the CPU (supercomputer NEC SX-2) for the iterative computation. In the rage of Re=64450, the present numerical scheme was validated through the comparisons between the numerical results and the corresponding experimental data which were also obtained in the present study.

A Study of the Molecular Mechanism of Vapour Condensation

Abstract: The condensation coefficient (c.c.) of vapour is investigated on the basis of the transition state theory which is treated in the framework of statistical mechanics of gases and liquids. The theoretical c.c. is reconfirmed to be the ratio of the rotational partition function of a liquid molecule to that of a vapour molecule and is given by thermodynamic quantities available in the literature. The applicability of the theory is clarified through a comparison of molecular flux equation at the vapour-liquid interface with rigorous molecular flux equations based on the molecular gas dynamics of the monoatomic molecules

Research on fins for air conditioning heat exchangers : 1st report, numerical analysis of heat transfer on louvered fins

Abstract: This study involves to the analysis of fins used in various types of compact heat exchangers for automotive and room air conditioners. The numerical analysis method used in this study employs an oblique grid fitting to an inclining fin so that the analysis can be applied to various types of fins. It has been clarified that the visual streamline of flow visualization for louvered fins corresponds to the results of this numerical calculation, and that the pattern of the streamline affects the heat transfer performance of the louvered fins

Numerical Flow Analysis in a Cubic Cavity by the GSMAC Finite-Element Method : In the Case Where the Reynolds Numbers are 1000 and 3200

Abstract: In previous simulations, the modified GSMAC method, which is more applicable to in-out flow problems, was proposed. This scheme is extended to three-dimensional analysis. As an example, flow in a cubic lid-driven cavity having many verified experimental and numerical results has been calculated at the Reynolds numbers of 1000 and 3200

An experiment on a taylor vortex flow in a gap with a small aspect ratio :bifurcation of flows in a symmetric system

Abstract: Both Taylor vortex flows in a symmetric or asymmetric system exhibit various patterns (cell modes). They can be classified by the process of cell formation, the number of cells and the direction of flow for the cell, into primary modes or secondary modes, and normal modes or anomalous modes. Following the previous report in which flows in a symmetric end condition were classified, in the present work, for flows in an asymmetric end condition, the Reynolds number at which a secondary mode bifurcates into another mode is experimentally investigated, and the bifurcation of the Taylor vortex flows in an asymmetric system when the Reynolds number is gradually decreased is presented in a bifurcation diagram.

A peculiar behavior of cavitation-nuclei-size distributions in sample water under vibratory erosion tests

Abstract: In order to clarify the necessary conditions for cavitation-erosion tests with a vibratory apparatus, we carefully measure the cavitation-nuclei-size distributions and the relative air content rate of test water with respect to time by means of a Coulter counter and a van Slyke apparatus, respectively

Flow-Induced Vibration of Long-Span Gates : Verification of Added Mass and Fluid Damping

Abstract: The added mass and the fluid damping coefficient were derived theoretically in a dimensionless form in a previous study. To verify the theoretical results of the added mass and the fluid damping coefficient, the experimental results of a model test are presented in this study. A planar vertical gate undergoes free damped vibrations in air and still water. The added mass and the fluid damping coefficient are calculated from the measured frequencies and damping ratios of the damped vibrations. Consequently, it is shown that there is good agreement between the theoretical and experimental results

An Experimental Study on an Underexpanded Annular Impinging Jet

Abstract: An underexpanded annular impinging jet is studied experimentally. The aerodynamic characteristics of the impinging jet depend significantly on the distance H between the nozzle exit plane and the impinged flat plate. The annular impinging jet diverges in the downstream direction provided H is smaller than a critical value H c . The feature of the jet changes significantly at H=H c

Heat Transfer Characteristics in Narrow Vertical Rectangular Channels Heated from Both Sides

Abstract: The effects of gap size on heat transfer characteristics were investigated experimentally for a vertical rectangular flow channel with gaps of 2.5 mm, 6 mm and 18 mm

Fully Developed Turbulent Flows through Rectangular Ducts with One Roughened Wall

Abstract: Two ducts, one with a long-side rough wall and the other with a short-side rough wall, have been used. The distributions of the mean velocities and turbulent stresses over a whole cross section in the fully developed region were measured by hot-wire anemometry. The secondary flow distributions in both the rough ducts were remarkably different from those in the smooth-walled duct

Structure of Propane Jet Diffusion Flame in a Cross Flow

Abstract: An experimental study was made of the structure of the propane jet diffusion flame discharged normal to a free stream of air with a uniform velocity profile. The velocity profile in the flame was measured by application of the forward scattering LDV system. A gas chromatograph was available to measure the concentration profile of the major species in the flame. The results showed that the flame configuration were correlated well with the ratio of the discharging velocity of the propane jet to the air velocity. The transition from an eliptic to a crescent shape was observed in the contour of the constant velocity in the transverse cross section normal to the jet axis of the flame. A peak in the CO concentration profile was observed below the jet axis where the propane concentration showed a maximum, and above the location of minimum O2 concentration. The CO2 concentration profile had two peaks which bore a resemblance to the temperature profile.