FLOW ANALYSIS AND PRESSURE MEASUREMENT AROUND A CAPSULE IN A CAPSULE TRANSPORTATION SYSTEM

摘要

Many of the various systems currently used for transportation involve such problems as noise and harmful emissions. With increasing environmental awareness, there is a strong demand for transportation systems free of such problems. One such transportation systems is the pneumatic capsule transportation systems. It can reduce noise by using a centralized power source, and at the same time it involves little danger of air pollution because it transports materials in capsules through a pipeline. The pneumatic capsule transportation system is a promising environmentally compatible system for the future. Despite the bright prospects, however, not much research has been performed on capsule transportation systems. Most of the research deals with the dynamic characteristics of the capsule, and the dynamics of the flow around the capsule is largely ignored. Nevertheless, the analysis of the flow around the capsule is an important subject, because the dynamic characteristics of the capsule depend on both the pressure difference across the capsule and on drag. The capsule transportation system discussed in this paper has a very small clearance between the capsule and the pipe wall, and thus it is very difficult to measure the velocity and pressure distributions in the clearance. Computational fluid dynamics (CFD) is one method for analyzing a flow field that is difficult to examine by experiment. CFD provides detailed information about the flow that cannot be measured by experiment. In this study, the compressible Navier-Stokes equation was analyzed by finite difference computations in order to estimate the flow field around the capsule. Also, there is a fast flow between the capsule and pipe wall, and it is expected that a shock wave is produced there. To capture the shock wave with high accuracy, the Total Variation Diminishing (TVD) scheme was employed. A small experimental apparatus was used to measure the pressure in order to evaluate the reliability of computed results. On the basis of these results, the effectiveness of CFD for the prediction of the flow around the capsule was investigated.