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To study the time-averaged flow field characteristics of a cylinder under the action of periodic oscillating flow, the time-varying flow field around the cylinder was obtained by numerically solving the Navier-Stokes equations. The time-averaged flow field was obtained by averaging the velocity field over time. The time-averaged flow fields with different KC numbers under a given Stokes number β=20 for Reynolds number Re< 200 were compared and analyzed. It is found that: (1) when KC< 7 (Re<140), the oscillating flow vorticity source is always attached to the cylinder wall and gradually stretches along the oscillating flow direction; (2) the corresponding time-averaged flow field consists of four small-scale internal vortices with strong stable flow and four large-scale external vortices with weak flow; (3) the flow structure is of axisymmetric distribution; (4) when KC> 7 (140<Re<200), the symmetry of the vorticity distribution around the cylinder is destroyed, while the oblique vortex street and dissipative behavior appear, the corresponding time-averaged flow field structure is seriously distorted, and the flow field structure is closely related to the vortex shedding mode around the cylinder, (5) the strength of the time-averaged flow field increases exponentially with the increase of KC number, and (6) for double cylindrical tubes, the time-averaged flow fields under different arrangements and spacing ratios show rich flow field characteristics, and the gap flow intensity between tubes increases with the decrease of spacing ratio.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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