Effects of free-stream perturbations on low-frequency embedded in the vortex shedding process

Chin Tsan Wang, Jiun-Jih Miau

Research output: Contribution to journalArticlepeer-review

Abstract

Some thoughts on the low frequency unsteadiness by upstream disturbances were explored. Results were found by flow visualizations of water channel. First, the affected region of local disturbance produced by an upstream cylinder induced spanwise motions of separated shear layers at Re=1220. Outside of the affected region due to the cylinder wake, spanwise shedding-vortex structures in the unaffected region appeared well organized. Second, results also showed that high nonhomogeneous intensities would induce large spanwise oscillation of separated shear layers behind the bluff body. On the other aspect, an integral time scale (It) and a span-wise characteristic length scale of the low frequency variations were investigated in the wind tunnel at different upstream turbulence levels produced by situating a control cylinder or a mesh at Reynolds number in the order of 104 to study the relations between the upstream turbulence intensity and low-frequency variations. Results indicate that the integral time scale of low-frequency variations is 2.4 Ts at the flow field of situating upstream cylinder and is 20% larger than the integral time scale, 2 Ts, corresponding to the flow field without upstream turbulence. The three-dimensional flow characteristics in the near wake region can be illustrated by the correlation of base pressure signals at different spanwise locations at the nonhomogeneous upstream turbulence flow field of situating upstream mesh. Results show that the spanwise coherence of low-frequency variations at non-homogeneous upstream turbulence level is better than that of the flow field without upstream turbulence. The spanwise length scale characterizing low-frequency variations could be significantly larger than D=32 mm.

Original languageEnglish
Pages (from-to)537-540
Number of pages4
JournalJournal of the Chinese Society of Mechanical Engineers, Transactions of the Chinese Institute of Engineers, Series C/Chung-Kuo Chi Hsueh Kung Ch'eng Hsuebo Pao
Volume24
Issue number5
Publication statusPublished - 2003 Oct 1

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering

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