Katsuhiko Hojo

Visualization of the flow around a cylinder with a small object

The force which such a model as a cylinder or a square cylinder receives from an uniform flow is well known to be reduced by the small objects arranged in the upstream side of the model. In this study, the effect of the number of the small objects, their arrangement and their shapes on the flow around a cylinder is examined using a flow visualization. The location of vortex in the downstream side of a cylinder and Strauhal number of vortex releasing are examined using the obtained images in this study. And, the location of the vortex is also examined in the case of the plate arranged in the downstream side of a cylinder.

Discussion on Estimation Method of Flow Fields by PIV Combined with CFD

The velocities at multiple points in a space can be examined simultaneously by Particle Image Velocimetry(PIV) without touching the flow fields. PIV is also studied actively because it is an effective measuring method. But, it is well known that many images are not usually obtained in the neighborhood of an obstacle or a wall surface. Therefore, the accuracy of the velocity vector obtained at such a location is still not satisfactory.In this study, we propose the calculation method in which the optimization technique based on N-S equations and the pressure-information in the cell near a wall surface are applied to the velocity vector obtained by PIV. In this report, it is applied to a two-dimensional cavity flow using the simulation data of pressure.

Thermal diffusivity and porosity of solid materials by the electromagnetic ultrasonic technique. Part 3—simultaneous measurement of ultrasonic velocity and thermal diffusivity

The objective of this study is to evaluate simultaneously the time dependence of the thermal diffusivity of carbon-carbon composites (C/C composites) and their porosity during heat treatment using the electromagnetic ultrasonic technique. This paper describes two kinds of experiments conducted to confirm the principle for simultaneous measurement of both the ultrasonic velocity (used to evaluate the porosity) and the thermal diffusivity at room temperature. For each material, the samples used in both experiments were identical. The ultrasonic velocity of type 304 stainless steel and its thermal diffusivity were 5.85 km/s and 3.8 mm2/s with precisions of ±1.6 and ±8 percent, respectively. The ultrasonic velocity of a two-dimensional woven C/C composite and its thermal diffusivity were 2.86 km/s and 4.8 mm2/s with precisions of ±5.0 and ±8 percent, respectively. The results appear to indicate that the electromagnetic ultrasonic technique can measure the ultrasonic velocity and the thermal diffusivity simultaneously and that it is also applicable to C/C composites.