Tetuya Kawamura

Numerical simulation of three-dimensional flow structure in a driven cavity

Investigations have been made of three-dimensional flows of an incompressible viscous fluid in a square cubic cavity. The flows are driven by the sliding upper surface of the cavity. Numerical solutions are obtained by directly integrating the full, three-dimensional, time-dependent Navier-Stokes equations. The three-dimensional flow structure is examined in detail over a wide range of the Reynolds number Re. One primary finding of these three-dimensional numerical simulations indicates that steady solutions are attained at lower values of Re, but the flow becomes unsteady at higher values, say, when Re exceeds approximately 2000. Due to the profound influence of the endwall effects, three-dimensional flows show substantial differences from two-dimensional solutions: for two-dimensional flow situations, steady solutions are known to exist for up to Re = 10000. The three-dimensional flow structure displays qualitatively distinct features in the low-Re and high-Re regimes. The demarcation separating these two regimes appears to lie in the neighborhood of Re = 2000–3000. One principal characteristic is that the Taylor-Gortler-like vortices are discernible for the high-Re regimes, although these have not been clearly captured in the numerical results for the low-Re regimes. Critical assessments of the present numerical results have been made by cross-checking the data with the available experimental measurements for three-dimensional cavity flows. The comparisons demonstrate broad qualitative agreement between the present numerical computational results and the laboratory measurement data.

Numerical Study of the Formation of Transverse Dunes and Linear Dunes

Transverse dunes and linear dunes are simulated numerically in order to make clear the mechanism of the formation of two kinds of typical sand dunes. The numerical method employed in this study can be divided into three parts: (i) Calculation of the air flow above the sand dunes; (ii) Estimation of the sand transfer caused by the flow through the friction; (iii) Determination of the shape of the sand ground. Since the computational area has been changed due to the last step, these procedures are repeated until typical shapes of the sand dunes are formed. One kind of the simulated dunes, which is formed by one wind direction, becomes essentially parallel straight ridges at right angle to the wind direction with only one slip-face on the lee side, which is known as the transverse dunes; The other one, which is formed by two directional wind, becomes essentially parallel straight ridge at the converging direction with two slip-faces on both sides, which is known as linear dunes.

Numerical Study of the Magnetic Effect on the Compressive Air Flow at an Intake

Air flows under a magnetic field at an intake are examined by means of numerical simulation. The air flow is caused by the pressure difference and the flow rate is measured to determine the effect of the magnetic field at the intake. The flow is assumed to be compressible and inviscid. Under the magnetic field, the air flow rate at the intake is more than double that without the magnetic field after having reached steady flow. Even in the inviscid flow, vortices are generated under the magnetic field and after their movement the air flow increased markedly.

Numerical Study of the Flow Around the High-torque Wind Turbine of Vertical Axis Type

Numerical simulations of two-dimensional flows around a vertical axis type wind turbine are investigated. The turbines studied in this paper are the Savonius turbine and the cross-flow turbine of twelve blades. The governing equations are the incompressible Navier-Stokes equations. A rotational coordinate system, which rotates at the same speed of the turbine, is used in order to simplify the boundary conditions on the blades. Additionally, a boundary fitted coordinate system is employed in order to express the shape of the blades precisely. The fractional step method is used to solve the basic equations. A third order upwind scheme is chosen for the approximation of non-linear terms. The results are compared with experiments and agreements are reasonable.

Simulation of Thermal Convection in a Stratified Fluid Flow

A new method to simulate thermal convection in a stratified fluid flow has developed. In the present method, the compressible Navier-Stokes equations are modified, based on the assumption that flow speed is in a subsonic range. The basic equations are obtained similar to the incompressible equations as a result of the formulation. Using these basic equations, thermal convection in a stratified fluid flow is simulated with a multidirectional finite-difference method in 3-dimensional Cartesian coordinates system.

Computation of The Flow Around a Bluff Body By Multi-Directional Finite Difference Method

We present calculation of compressible flow based on solving the Navier-Stokes equations at equal intervals in Cartesian coordinate system. For a fundamental understanding of unsteady flow, we apply the multi-directional upwind finite difference method to the compressible flow past bluff bodies of various shapes. In order to catch the complicated nature of flows around bluff bodies, it is effective to use the multi-directional finite difference method for all the space derivative terms.

The Coupled Analysis of Pipe Burst and Multicomponents Fluid of Very High Pressured Natural Gas Pipeline

The decompression of natural gas is slower than one of ideal gas. The two-dimensional coupled analysis of fluid and structure is developed. The large inertia force continues pipe deformation, although the pressure load on pipe wall is weakened drastically. At the boundary of air and natural gas, large gradient of temperature is observed. The liquefaction of expanded natural gas is observed.

Numerical Study of The Interference Effects in Small Vertical Axis Wind Turbines

Two dimensional flows around multiple small wind turbines installed in a line are investigated by numerical simulation. The turbines which studied in this research are cross-flow type with vertical axis. Incompressible Navier-Stokes equation is solved by the finite difference method based on the Fractional Step method. Overset grid system is employed in this simulation. A rotating coordinate system, which rotates at the same speed of the turbines, is used for a vicinity of the rotor and a stationary coordinate system is used for the other area. The interference among lined cross-flow wind turbines is investigated for their urban area use.Copyright

Molecular Dynamics Simulation of Oxygen Recombination on Finite Catalytic Surface

In this paper, the behaviors of oxygen atoms on the surface of silica are investigated by classical molecular dynamics simulation for the detailed mechanism on surface catalysis. Three types surface of β-cristobalite are formed with BMH potential and three-body potential. The temperature dependency of mobility and proximity about two bared oxygen atoms is observed and the result supports one of the proposed surface catalysis mechanisms.

Numerical Simulation on the Propagation of an Internal Wave in Multifluid

We numerically investigate the propagation of surface and internal waves which are caused by a gravity current in a container. A level set approach is used to capture interfaces without explicit tracking. To model the complex boundary of the container, a virtual boundary method is applied to the level set formulation. In this study, it is shown that multifluid flows in a deformed container can be simulated through the combination of the above two methods.