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|Other Titles: ||Freestream turbulence effects on flow characteristics of separated and reattached flows|
|Authors: ||陳增源;Chen, Tzeng-yuan;施建宇;Shih, Jian-yu|
|Keywords: ||三維分離及再接觸流;再接觸長度;紊流度;Three-dimensional separated and reattached flow;Reattachment length;Turbulence intensity|
|Issue Date: ||2010-08-09 19:28:17 (UTC+8)|
The research experimentally investigates the freestream turbulence effects on flow characteristics of three-dimensional separated and reattached flows. A backward-facing step duct and cylinder-type turbulators are used to generate different levels of turbulence on the inlet freestream. The Reynolds numbers range from 500 to 18000, which cover the laminar, transitional and turbulent flows. The measurements include the reattachment length, the spanwise distributions of reattachment length, and the turbulent intensity distributions near the step-wall using laser Doppler velocimetry. Results of this study show that the freestream turbulence effects on the reattachment length are to (1) shorten the reattachment length, especially in transitional flow regions, (2) reduce the Reynolds numbers for the onset of transitional and turbulent flows, i.e., cause the transitional and turbulent flows occurring early, (3) reduce the Reynolds number range of the transitional flow. The freestream turbulence effects on the spanwise distribution of reattachment length are to (1) cause some loss of the symmetry of the spanwise distribution of reattachment length with respect to the duct center, (2) cause the reattachment length varied in the duct center region, (3) move the location of minimum reattachment length toward the duct center, (4) make the spanwise distribution of reattachment length decreasing and, then, increasing more clearly approaching the sidewall. Results of this study also show that the freestream turbulence generally does not change the distributions of near-wall turbulent intensity. The maximum near-wall turbulent intensity occurs approximately at reattachment under turbulent flow conditions, while the streamwise distributions of near-wall turbulent intensity are generally constant under laminar flow conditions. However, the freestream turbulence increases and decreases the near-wall turbulent intensity inside and outside of the recirculation zone, respectively, under turbulent flow conditions, and increases the near-wall turbulent intensity both inside and outside of the recirculation zone under laminar flow conditions.
|Relation: ||航空、太空及民航學刊系列 B = Journal of Aeronautics, Astronautics and Aviation, Series B 40(2), pp.85-91|
|Appears in Collections:||[Graduate Institute & Department of Aerospace Engineering] Journal Article|
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