Fundamental studies on free stream acceleration effect on drag force in bluff bodies |
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Authors: | Yeongbin Lee Joohyun Rho Kyu Hong Kim Dong-Ho Lee |
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Affiliation: | 1.School of Mechanical and Aerospace Engineering,Seoul National University,Seoul,Korea;2.School of Mechanical and Aerospace Engineering/Institute of Advanced Aerospace Technology,Seoul National University,Seoul,Korea |
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Abstract: | This paper describes fundamental studies on free stream acceleration effect on drag force in bluff bodies. The flow with gradual
velocity increase assumed an accelerated flow. The wind tunnel tests were conducted in order to investigate the difference
of aerodynamic characteristics between non-accelerated flow and accelerated flow. The experimental models were a circular
cylinder and a square cylinder. In an accelerated flow, the condition of free stream was an acceleration of about 3.6m/s2. Experimental Reynolds number varied between form 4.0×104 to 1.64×105. The pressure distributions and the aerodynamic force were measured in both case of nonaccelerated flow and accelerated flow.
In case of a circular cylinder, the drag of accelerated flow is lower than that of non-accelerated flow in the low Reynolds
number regime. Then, it becomes higher than that of non-accelerated flow in the high Reynolds number regime. On the other
hand, in case of a square cylinder, the drag of accelerated flow is higher than that of non-accelerated flow in the whole
Reynolds number regime. If a separation point can be movable such as the circular cylinder, the additional momentum due to
flow acceleration leads to delay separation and to decrease the drag in the low Reynolds number regime. If a separation point
is nearly fixed such as a square cylinder, the additional momentum due to acceleration always affects to increase the drag
than that of non-accelerated flow. Based on this research, it is expected that the roof shape of high speed train where the
separation point is movable has the advantages to reduce the effect of accelerated flow such as strong crosswind/gust. |
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