Transactions of the Korean Society of Mechanical Engineers B (대한기계학회논문집B)

The Korean Society of Mechanical Engineers (대한기계학회)
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Experimental Study on Flow Structure of Wake Behind a Rotationally Oscillating Circular Cylinder

주기적으로 회전진동하는 원주 후류의 유동구조에 관한 실험적 연구

  • 이정엽 (포항공과대학교 대학원 기계공학과) ;
  • 이상준 (포항공과대학교 기계공학과)
  • Published : 2006.04.01
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Abstract

The flow around a circular cylinder which oscillates rotationally with a relatively high forcing frequency has been investigated experimentally using flow visualization and hot-wire measurements. Dominant parameters are Reynolds number (Re), oscillation amplitude $({\theta}_A)$, and frequency ratio $F_R=f_f/f_n$, where $f_f$ is the forcing frequency and $f_n$ is the natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\theta}_A={\pi}/6$, and $0{\leq}F_R{\leq}2$. The effect of frequency ratio $F_R$ on the flow structure of wake was evaluated by measuring wake velocity profile and spectral analysis of hot-wire signal. Depending on the frequency ratio $F_R$, the cylinder wake has 5 different flow regimes. The vortex formation length and vortex shedding frequency are changed significantly before and after the lock-on regime. The drag coefficient was reduced under the condition of $F_R<1.0$ and the maximum drag reduction is about 33% at $F_R=0.8$. However, the drag is increased as $F_R$ increases beyond $F_R=1.0$. This active flow control method can be effective in aerodynamic applications, if the forcing parameters are selected optimally.

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References

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