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ISSN オンライン: 2642-0554

A SPATIAL STRUCTURE OF A FLOW OF AXISYMMETRIC SUDDEN EXPANSION

Noriyuki Furuichi
Department of Mechanical System Engineering, Gifu University Yanagido 1-1, Gifu 501-1193, Japan; Paul Scherrer Insitut CH5232 Villigen PSI, Switzerland; National Metrology Institute of Japan National Institute of Advanced Industrial Science and Technology. 1-1-1 Umezono, Tsukuba, 305-8563, Japan

Yasushi Takeda
Paul Scherrer Institute CH-5232, Villigen PSI, Switzerland

Masaya Kumada
Department of Mechanical Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan

要約

A flow transition for an axiymetric sudden expansion was experimentally investigated. Spatio-temporal flow field measured using ultrasonic velocity profiler and analyzed by a two-dimensional Fourier transform and a proper orthogonal decomposition. The variation of the zero-cross point of the axial velocity distribution, the energy of velocity fluctuation directed to upstream and the eigenmode spectrum have the same transitional scheme with respect to Reynolds number. The transitional scheme can be classified as laminar flow for Red < 1000, and transitional regime for Red = 1000−4000 and turbulent regime for Red > 4000. We found that the two large change occurs in the transitional regime at around Red = 1500 and 2000. The jump that occurs at Red = 2000 is caused by the change of the flow condition in the upstream pipe. The jump at Red = 1500 shows a change of the spatial structure of the flow.