Takanobu Ogawa

Numerical investigation of three-dimensional compressible flows induced by a train moving into a tunnel

Abstract A three-dimensional flow induced by a practical high-speed train moving into a tunnel is studied by the computation of the compressible Navier-Stokes equations with the zonal method. The transient flow field induced by tunnel entry is investigated with the focus on the compression wave which is the source of the booming noise at the tunnel exit. The results reveal a pressure increase inside the tunnel before tunnel entry, the one-dimensionality of the compression wave, the histories of the aerodynamic forces, etc. The computed pressure histories inside the tunnel agree with the field measurement data. The flow fields are also computed for cases where the train runs on differently positioned tracks into the tunnel. The results indicate that the wavefront of the compression wave is affected by the train position and this phenomenon is explained by the parameter υwatt.

Aerodynamics of high speed trains passing by each other

A three-dimensional flow field induced by two trains passing by each other inside a tunnel is studied based on the numerical simulation of the three-dimensional compressible Euler/Navier-Stokes equations formulated in the finite difference approximation. A domain decomposition method with the FSA (fortified solution algorithm) interface scheme is used to treat this moving-body problem. The computed results show the basic characteristics of the flow field created when two trains pass by each other. The history of the pressure distributions and the aerodynamic forces acting on the trains are the main areas discussed. The results indicate that the phenomenon is complicated due to the interaction of the flow induced by the two trains. Strong side forces occur between the two trains when the front portion of the opposite train passes by. The forces fluctuate rapidly and the maximum suction force occurs when two trains are aligned side by side. The results also indicate the effectiveness of the present numerical method calculating moving boundary problems.

An Efficient Numerical Algorithm for the Tree-data Based Flow Solver

An efficient numerical algorithm is developed for the tree data structure which have been widely used for the adaptive Cartesian mesh method. A simple neighbor cell finding with a “pedigree” and implementation of the implicit scheme and the Multigrid method are presented. It is found that the numerical schemes developed for the conventional flow solver can be easily implemented to the tree-data based flow solver.

Development of a flow solver using the adaptive Cartesian mesh algorithm for wind environment assessment

Abstract A new flow solver is developed for wind environment assessment in which a very complex flow field over a number of buildings should be taken into account. The adaptive Cartesian mesh algorithm is used so as to automatically generate meshes for complicated flow geometry. In this approach, a flow field is decomposed into a number of cubic cells and a cell is recursively divided into eight children cells where curvature of flow geometry or gradient of flow variables are large. The numerical scheme is based on the artificial compressibility method and the finite volume method is used for discretization. The cells are organized with the tree data structure and the numerical algorithm for the tree data structure is described. Computational results are presented and the efficiency of the algorithm is discussed.