Ryuichiro Yamane

Effect of non-Newtonian property of blood on flow through a stenosed tube

It is well known that the fluid dynamics of arterial blood flow plays an important role in arterial diseases. Periodic blood flow through a stenosed tube was analyzed numerically. The bi-viscosity model is used as a constitutive equation for blood, and the flow is assumed to be periodic, incompressible and axisymmetric. Effects of pulsation and the rheological property of blood are considered. The flow pattern, separated region and the distributions of pressure and shear stress at the wall are obtained. The results show that the non-Newtonian property reduces the strength of the vortex downstream of stenosis and has considerable influence on the flow even at high Stokes and Reynolds numbers, provided that pulsatile flow has a stagnant period.

Vortex enhancement in blood flow through stenosed and locally expanded tubes

It is well known that fluid dynamical phenomena in arterial blood flow can play an important role in arterial diseases. Periodic blood flow through stenosed and locally expanded tubes is analyzed numerically. The fluid is assumed to be non-Newtonian and incompressible, and the flow is assumed to be periodic in time and axisymmetric. It is found that the vortex downstream of stenosis or expansion becomes strongest at a certain frequency of pulsation. This phenomenon is called vortex enhancement in this paper. The flow pattern, separated region and the distributions of pressure and shear stress on the wall are obtained. The results show that the vortex enhancement occurs in both tubes. The vortex enhancement occurs where the difference between the adverse pressure and the friction on the wall is a maximum.

Ferromagnetic fluid flows in a rectangular channel with travelling magnetic fields

Abstract Experiments were made on the laminar flow of a water-based ferromagnetic fluid with alternating, travelling magnetic field from 3 to 50 Hz. The pressure difference was found to be induced in the opposite direction to the field, but it was so small to be appreciable at high Reynolds numbers.

Axial oscillation of a magnetically levitated non-magnetic fluid column inside a straight magnetic pipe

The axial oscillation of a magnetically levitated non-magnetic liquid column in a magnetic fluid and a non-uniform weak magnetic field is studied theoretically and experimentally. The angular speed equation and wave speed equation of the interfacial wave are derived from the ferrohydrodynamics Navier–Stokes equation in a given magnetic field by (1) omitting the non-linear terms, (2) assuming that the undisturbed interface between the levitated fluid and the surrounding fluid is an infinite long cylindrical surface, and (3) assuming that the disturbance is an axisymmetric axial one of small amplitude. The experimental study is made by setting two very long permanent magnetic north poles face to face with each other to form the non-uniform magnetic field, using silicon oil as the levitated fluid and using a diluted water-based magnetic fluid as the surrounding fluid.

Coherent structure in the turbulent wake behind a circular cylinder

A wake behind a circular cylinder at Reynolds number 850–1700 was visualized by the smoke-wire method. The observations of the How together with the results of quantitative measurements, such as various velocity correlation coefficients, illustrated the formation process of spoon-shaped large eddies in the region 90 ≤ x/d ≤ 230 attained through the deformation and rearrangement of the regular Karman vortices. A spoon vortex was likely to pair with the counterpart on the opposite side of the wake. The large-scale bulges of the turbulent and non-turbulent interface of the wake were shown to correspond to these spoon vortices. These results indicate that some coherent structures are organized by rearrangement and deformation of initially regular vortices in turbulent flow.

Local velocity measurement of magnetic fluid flow using laser optical fiber sensor

Abstract The local velocity of an open channel flow of magnetic fluid in a traveling magnetic field is measured using a laser optical fiber sensor. The measured velocity distributions are compared with the theoretical ones. The shapes of the distributions are quite different from those of nonmagnetic fluid flow.

Interfacial waves of the magnetic fluid in vertical alternating magnetic fields

Abstract The stability of the surface of a magnetic fluid layer under the influences of vertical alternating magnetic fields was investigated experimentally and analytically. Two kinds of waves were excited on the surface and the critical conditions for the onset and the wavelength of these waves were obtained.

Coherent structure in the turbulent wake behind a circular cylinder 2. Numerical simulation using the vortex filament model

In the previous paper the authors reported observing the formation of a spoon-shaped vortex chain in a wake behind a circular cylinder as a coherent structure in turbulence. In this report numerical simulation is carried out based on the assumption that the structure is formed by deformation of the Kannan vortices. The basic equation is the localized induction equation for a single vortex filament with an influence of the background mean flow. The vortex filament is given an initial deformation within a plane at an angle θ to the x–z plane (x is the mean flow direct and z the spanwise direction) with the width Zw, and the further deformation process of the filament is numerically traced. The first calculation is made with fixed Zw and various values of θ. The result shows that the vortex filament finally reaches a structure lying on a plane with a constant angle of 30° ~ 45° to the x-z plane irrespective of the initial values of θ. The second calculation is made with fixed θ and various values of Zw. In this case the final spanwise scale of the deformed region of the filament has almost constant values of about 4d–6d (d is diameter of the cylinder). These results indicate that the final structure of the vortex filament is stable and definite irrespective of the initial disturbances.

Soliton wave in a magnetically levitated diamagnetic liquid column

In the flow regulation of a magnetically levitated pipeless flow system, solitary waves may occur, which will lead to pressure fluctuations and surface changes of the levitated diamagnetic liquid column. The present study analyses a soliton in a magnetic pipe both theoretically and experimentally. A two-fluid model is employed here. The theoretical analysis is carried out by a one-dimensional nonviscous and nonlinear method. The experimental study was also carried out by setting two magnetic like poles to produce the magnetic field, using water as the levitated diamagnetic liquid and a diluted kerosene-base magnetic fluid as the surrounding fluid, coupled with a cam system to produce the disturbance. It is found that the magnetic pressure acting on the interface can stabilize the interface. The effects of the magnetic bond number, density ratio of the two fluids and amplitude of the soliton on the soliton wave velocity are clarified.

Multi-step positioning control using a binary digital pneumatic-cylinder system

This paper presents an analysis of the dynamics of binary digital pneumatic-cylinder systems, which was undertaken to achieve multi-step positioning control. Based on an experimental system and a new algorithm for numerical analysis, the positioning control problem was investigated by means of simulations and experiments under various load conditions. Two methods are proposed to improve the transient response during positioning: timing control and braking control.