Shigeaki Kuroda

Lubrication with emulsion: first report, the extended Reynolds equation

A simplified model based on the continuum theory of mixtures is proposed to derive the extended Reynolds equation for lubrication with emulsion. This model has showed that there is a velocity difference between two phases of emulsion. The existence of the velocity difference is the reason why the oil concentration varies in lubrication film. Using this equation, the pressure distribution and the variation of oil concentration can be obtained simultaneously, and the mechanisms of lubrication in the three-speed regions can be explained.

Lubrication with emulsion. II. The viscosity coefficients of emulsions

Abstract The viscosity coefficients of emulsions—which relate to the extended Reynolds equation for lubrication with emulsion—have been investigated and two set of formulas are suggested to determine them. The formulas are suitable for two different states of emulsion, i.e. in the thick film zone and in the thin film zone. On this basis, we discuss the variation of the oil concentration along the lubrication film, as well as the reason why the elastohydrodynamic lubrication film thickness of emulsions is of the same order as that of neat oils.

Use of a strain gauge accelerometer in the aerodynamic study of a spherical body at free fall

Free fall tests of a spherical body of 10 cm diameter with a built-in acceleration sensor of the strain gauge type have been carried out under both smooth and disturbed surface conditions. The acceleration data are stored in a memory in the body during the motion, and transmitted to an external host computer after the landing for processing and analysis. It has been demonstrated from these data that the aerodynamic forces acting on the sphere, and hence its falling distance as well as its velocity, can readily be determined with sufficient accuracy. The results are fully consistent with those obtained in the previous study from the surface pressure measurements on a similar sphere at free fall. The effects on the drag force of a surface trip ring to disturb the boundary layer are also discussed in some detail.

The Effects of the Wall-Layer Models on the Outer Turbulence Structures in Large Eddy Simulation of Pipe Flows

Reproduction of the outer turbulence in Large Eddy Simulation (LES), when the wall-layer model is adopted in the inner layer, is investigated to validate the hybrid RANS/LES as an approximate near-wall treatment. Special emphasis is on the possibility of Detached Eddy Simulation (DES) for the reproduction of outer large (∼ R) and very large (∼ 10 R) streaky structures typically observed in the pipe turbulence. LES and DES of fully developed turbulent pipe flows at the friction Reynolds number up to 5000 are conducted using a very long analysis region to capture entire outer scales. It is found that the outer scales are properly captured in DES independent on the unphysical super-streaks in the RANS region near the wall, as long as sufficient height for the DES buffer layer is maintained. Our results shed light on the origin of the outer structures, which are rather autonomous similar to the inner sublayer streaks, and these two structures with different scaling exists in the isolated manner.Copyright

Numerical Analysis of Moving Boundary Problems Using Cartesian Grid Method

Recently, the Cartesian grid method was used on simulations of fluid flow around the complex geometry problems. In this paper, the Cartesian grid method with cut cells are used to simulate incompressible viscous flows around moving objects. In this study, the small cut cells are merged with neighboring cells. The code was developed based on Fractional Step Method on Finite Volume Method. In time integrate, the second order explicit Adams-Bashforth method was used for the convective terms and second order implicit Crank-Nicholson method was used for the diffusive terms. Some moving boundary problem are simulated using the presented code and compared with other previous numerical and experimental results.

Flows around an Arbitrary Shaped Body with Elastic Deformation by Fluid Force.

A new method for computation which make an analysis of flow field around an arbitrary shaped body with elastic deformation by fluid force have been developed. Non-linear simultaneous equations are derived from governing equations of flow field and elastic deformation, and then the non-linear simultaneous equations are solved using Nowton-Raphson method. An independent variable is only fluid force in the equation of elastic deformation. The flow field is defined as implicit function of the fluid force acting on an elastic boundary. The number of the unkown quantity in Newton-Raphson method decreases substantially. The velocity field and the pressure field are computed after the fluid force acting on an elastic boundary is obtained. In this paper, we explain the principle of the computational method, and then two examples of numerical simulation are shown. One is the flow-induced oscillation of three-dimensional circular cylinder that is supported elastically and another is the computation of flow around an elastic wing with pitching motion.

Flow around a Pitching Wing with a Bending Motion in a Uniform Flow.

Flows around a pitching wing with a bending motion in a uniform flow are studied numerically. A finite difference method based on Marker and Cell (MAC) methods is used to calculate the two dimensional incompressible Navier-Stokes equations. The third order upwind finite difference scheme is used. Body-fitted grid generation with moving boundaries is used to obtain the numerical solutions of the flow fields. The effects on the flow field of Reynolds number, pitching frequency and bending angles are studied numerically. The effects on CD of pitching motion and bending oscillation are obtained. The results shows that a thrust is generated on the pitching and bending wing.