Takanobu Ogawa

<title>Abstract</title> The present study investigates the flow field in a rinsing process of a beverage can numerically and experimentally. The three-dimensional Navier-Stokes equations are solved with a finite volume method along with the volume of fluid (VOF) method for free surface. The beverage can set upside down is transported with a constant velocity and rinsed with a water jet ejected from a nozzle below the can. The case of a can at rest is also simulated. The result shows that the ejected water impinges on the can bottom and spreads along the side surface of the can. Then, as it flows down toward the can mouth, its front surface forms splashes. For the stationary can case, after the jet impinges on the can bottom, it almost evenly spreads over the side surface. The water flows downward and becomes branched flows by fingering. The time average of VOF is calculated to visualize the regions rinsed by water. For the case of a moving can, only the top region of the can is rinsed, and the ratio of the rinsed region drops to 29% from 69% for the stationary case. The computed water surfaces qualitatively agree with the experimental result, but the shape of the front surface, such as splashes and fingerings, cannot be resolved with the simulation.

<title>Abstract</title> Micro air vehicles (MAVs) have been developed for many fields. The MAVs usually receive strong impact from a velocity change in time or space, and facilities for aerodynamic experiments of MAVs under a gusty environment have been required. The present study has developed a gust wind tunnel to generate unsteady and non-uniform flows. We developed a small wind tunnel with eight multi-fans and a shutter mechanism at the upstream of the test section. We controlled the outputs of the fans independently and obtained a linear shear layer with an error of 5 percent. The velocity gradient of the shear layer was from 5 to 8 s−1. The shutter mechanisms provided a longitudinal gust with the velocity change from 2 m/s to 10 m/s within 0.3 seconds.

<p>This paper proposes a measurement system to detect locally high temperature spaces. The indoor spaces of a building with unique design tend to have uneven temperature distribution. Therefore, energy consumption required for air conditioning control increases. It is thought that the energy efficiency required for air conditioning control would be improved if locally high temperature space can be measured and the information feedback to the controller. In this study, a measurement system using a mobile robot was developed to measure the temperature distribution of indoor spaces. We experimented using this system in a library with a unique design and succeeded to detect locally high temperature spaces.</p>

<p>A tube-type gas burner consists of a straight tube with a slit along it and discharges an air-gas mixture through the slit to produce a flame. The flow velocity from the slit depends on the pressure in the tube and the pressure loss at the slit, and it varies in the longitudinal direction of the tube. The resulting uneven flame degrades the quality of the burner. In this study, we develop a one-dimensional theoretical model of the flow in a tube with a slit. To validate the result of the theoretical model, we also conduct experiments and numerical simulations for the same flow field. We applied this theoretical model to a flow in a tube, 1m length, 40mm in diameter, with a slit 2.5mm wide. The end of the tube is closed. We also discuss the effect of the length of the burner on the unevenness.</p>

The near pressure field formed around a high-speed train causes a vibration problem such as window rattling in railside residential areas. This paper investigates the effect of a wall along a track on the near pressure field both theoretically and numerically. The potential flow model of a flow around a train shows that the pressure fluctuation is reduced by the velocity field of the doublet generated on the wall. From the result with the panel method, we also find that the pressure reduction by the wall is a function of the ratio of the wall height to the distance from the train and is independent of the wall position.

We have investigated hydrogen explosion risk and its mitigation, focusing on compact hydrogen refueling stations in urban areas. In this study, numerical analyses were performed of hydrogen blast propagation and the structural behavior of barrier walls. The explosive source was a prismatic 5.27 m3 volume that contained 30% hydrogen and 70% air. A reinforced concrete wall, 2 m tall by 10 m wide and 0.15 m thick, was set 2 or 4 m away from the front surface of the source. Each of the tests measured overpressures on the surfaces of the wall and on the ground, displacements of the wall and strains of the rebar inside the wall. The simulated overpressures were in good agreement with test results for all three test cases. DIANA, a finite element analysis code was used for the structural simulations of the barrier wall. The overpressures obtained by the blast simulations were used as external forces. The analyses simulated the displacements well.

An mesh generation method for an adaptive Cartesian mesh is developed based on the bottom-up approach in which the smallest meshes near a solid surface are generated first, then the surrounding coarser meshes are generated. The Bresenham's method, one of the rendering techniques in computer graphics, is used to detect intersection between a mesh and a solid surface. With this method, the number of the meshes to be detected can be minimized. The generated meshes are organized with the tree data structure. Utilizing the hierarchical property of the tree data structure, the surrounding meshes can be generated with a simple algorithm. Efficiency of the mesh generation method is presented.

The aim of this paper is to study the mechanism of the creation of coherent structures in the turbulent boundary layer. We expect the disturbance put into a boundary layer to play a significant role for the creation of coherent structures, so the turbulent boundary layer with a vortex ring put into it as a disturbance is studied, both experimentally and by numerical simulation using 3D discrete vortex method. The results of the experiment show that the vortex ring changes its direction and moves far from the wall, it leaves a flow pattern near the wall where the velocity is higher than the surrounding area. The high speed region is created by a pair of vortex structures which resemble the coherent structure in turbulent boudary layers. The same flow field is calculated with "Vortex Segment Model", in which the vorticity field is represented by large number of vortex segments. The same vortex pair as obtained from the experimental results also appear.