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

The Korean Society of Mechanical Engineers (대한기계학회)
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Measurements of Secondary Vortices in the Cylinder Wake by Three-Dimensional Phase-Averaging Technique Using Cinematic PIV Data

Cinematic PIV 데이터의 3차원 위상평균 기법을 이용한 실린더 후류의 2차 와류 측정

  • Seong, Jae-Yong (Dept.of Mechanical Aerospace Engineering, Graduate School of Seoul National University) ;
  • Yu, Jeong-Yeol (Dept.of Mechanical Aerospace Engineering, Seoul National University)
  • 성재용 (서울대학교 대학원 기계항공공학부) ;
  • 유정열 (서울대학교 기계항공공학부)
  • Published : 2000.11.01
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Abstract

Near-wake flow field downstream of a circular cylinder in the wake-transition regime where fine-scale secondary vortices have a spanwise wavelength of around one diameter has been studied by means of phase-averaging from cinematic PIV data. A cross-correlation algorithm in conjunction with the FFT(Fast Fourier Transform)analysis and an offset correlation technique is used for obtaining the velocity vectors. Which the help of very high sampling rate compared to the shedding frequency, it is possible to obtain phase-averaged flow fields although the shedding is not forced but natural. Phase -locked three-dimensional vortical structures are reconstructed form the phase-averaged data in one x-y(cross-sectional) and several z-x(spanwise-streamwise)planes. In this process of phase-averaging in a z-x plane, a technique to freeze the secondary vortices relative to the centerline is applied. The formation process of the secondary vortices is shown by considering spatial relations between the primary Karman and the secondary vortices and their temporal evolutions.

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References

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