防風柵形状および柵と車両の離隔の変化が流れ場と車両空力特性に及ぼす影響

抄録

To clarify the relationship between the downstream flow field of a windbreak fence and aerodynamic forces acting on a train placed downstream of the windbreak fence, wind tunnel tests with models were conducted. A 1/40-scale windbreak fence model (height H = 50 mm, hole diameter D = 0, 2, 6, and 10 mm, thickness T = 0.8, 1.6, 4.0, and 8.0 mm) and a vehicle model with square cross-section were used. Flow velocity and turbulence intensity were measured by PIV measurement. The pressure distribution around the train model was measured with differential pressure sensors. Effects of varying the thickness and hole diameter of the windbreak fence and the distance between the fence and the train on the flow fields and train aerodynamic characteristics are examined. As a result of the tests, pressure coefficients show that the pressure field on the upstream side of the train varies more considerably than that on the downstream side with varying the distance between the windbreak fence and the train. Hence, the variation of drag force is mainly caused by the change of pressure field on the upstream side of the train. The drag coefficient is minimized when the distance between the windbreak fence and the train is a certain value, which has been also shown in previous studies. In this study, the reason why the drag coefficient is minimized is clarified. Both averaged velocity and drag force acting on the train become lower as the ratio of fence thickness to hole diameter T/D becomes larger. Although T/D of real fences is about 0.1, T/D can be about 1 for wind tunnel tests. Hence, it is recommended that the ratio T/D of the fence model should be less than 1 for wind tunnel tests.