Shinsuke Tajiri

Direct simulation of sound and underwater sound generated by a water drop hitting a water surface using the finite difference lattice Boltzmann method

The sound and underwater sound emitted from a water drop colliding with a water surface are simulated by a new model of the finite difference lattice Boltzmann method. The two-particle immiscible fluid model is modified to simulate sound in the gas phase and underwater simultaneously. In the very early stage after the collision, sounds propagating into the gas and liquid phases are successively detected, and the effects of drop shape and gas bubbles are also observed.

Improvement of Two-Component Model of the Finite Difference Lattice Boltzmann Method for a Gas-Liquid Flow Simulation

An Improved model of the finite difference lattice Boltzmann method which allows us to consider gas-liquid two component flows with a large density ratio like air-water flows was proposed. Simulations of the two component fluids which have a free interface and a large density ratio were demonstrated. The model which has compressibility of fluid and allows us to consider the pressure waves propagating in water like water hammers was presented. The basic idea is to decrease a density fluctuation by giving a large pressure gradient. The compressibility of liquid was controlled by choosing the bulk modulus. In order to simulate immiscible two fluids, the modulated diffusion scheme proposed by Latva-Kokko et al. was employed. The scheme is able to produce a smooth interface by allowing a certain amount of interface diffusion. The continuum surface force proposed by Brackbill et al. was employed as surface tension. A collapse of liquid column was calculated in order to confirm the relation between the inertia of liquid with a large density and the gravity, and the appropriate result was obtained.Copyright

Direct simulations of cavity tones by the Finite Difference Lattice Boltzmann Method

We performed a direct simulation of two-dimensional cavity tone by the finite difference lattice Boltzmann method. The Mach number of the flow is 0.2, and the Reynolds number is 5.5 × 108. Sound emission is simple-source like and the Doppler effect is detected. The frequency of the sound agrees with the theoretical estimation based on a very simple feedback system based on the interaction of vortex and edge. Positive pressure sound is simple. However, negative pressure sound has two modes due to interaction between vortex and edge and to the Helmholtz resonator mode.

Simulation of Sound Emitted from Collision of Droplet with Shallow Water by the Lattice Boltzmann Method

The sound emitted from splash of water droplet colliding with shallow water is simulated by the finite difference lattice Boltzmann method. Two-particle immiscible fluid model is used, and the under water sound is considered by introducing the elasticity for the liquid phase. After the collision, sounds propagating into the gas and liquid phases are successively detected. The directivity of the sound is shown to depend on the depth of the water.

Novel Finite Difference Lattice Boltzmann Model for Gas‐Liquid Flow

A novel model for the finite difference lattice Boltzmann method is proposed to simulate gas‐liquid two‐phase flow. The effect of the large density difference is incorporated by applying acceleration modification which is deduced from macroscopic dynamics in this model. Compressibility of the fluid is adjustable. Surface tension effects are included by introducing a body force term based on the Continuum Surface Force (CSF) method. The recoloring step is replaced by a anti‐diffusion scheme. Here we present results for liquid column collapse and droplet splashing on a thin liquid film. Results are in good agreement with experiment.

Study of a Propulsive Nozzle for a Ship Directly Driven by High-Pressure Wave Generated by Air-Propane Mixture Combustion

We propose a new type of propulsive equipment for a ship in this paper. It is directly driven by the high-pressure wave generated by air-propane mixture combustion. The propulsive equipment is a simple structure consisting of a combustion tube and a semi-open-type nozzle. In order to clarify the mechanism of thrust generation, we measured the pressure fluctuation on the nozzle wall and the thrust for various angles of ejecting the pressure wave, and also we observed the flow in the two-dimensional nozzle by using a high speed motion camera. Water flow in the nozzle is accelerated momentarily by the pressure wave, and the bubble is exhausted to downstream while their expansion. It was clarified that the thrust strongly depends on the nozzle-wall angle, and the thrust for the nozzle-wall angle 45 degrees is higher than others in this experiment. The thrust of the nozzle was 42 N when the 400 kPa pressure wave is driven with added oxygen.

Study on Flow Phenomenon inside a Nozzle of a Ship Propulsion Equipment Directly Driven by High Pressure Air (Experimental Consideration of Flow inside a Nozzle According to Water-Flow Velocity)

An experimental study by means of pressure measurements and flow visualization was performed to investigate unsteady flows inside a two-dimensional semi-open-type nozzle for a ship propulsion equipment directly driven by high-pressure gas. We found that ejected gas phase and water-flow phase are separated clearly of themselves, and the interface of these phase behave like interfacial waves. It is clarified by flow visualization with a high speed motion camera and a circulating water channel that these interfacial waves change their shapes according to water-flow velocity. The interfacial wavelength becomes longer in response to increasing water-flow velocity, and the mechanism that obtains thrust on the nozzle-wall changes. The thrust and flow patterns for the intermittent gas ejection according to water-flow velocity are also clarified.