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

The Korean Society of Mechanical Engineers (대한기계학회)
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Wake-Induced Boundary Layer Transition on an Airfoil at Moderate Free-Stream Turbulence

자유유동 난류강도에 따른 익형 위 후류유도 경계층 천이의 거동

  • 박태춘 (서울대학교 마이크로열시스템연구센터) ;
  • 강신형 (서울대학교 기계항공공학부) ;
  • 전우평 (서울대학교 정밀기계설계공동연구소)
  • Published : 2006.09.01
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Abstract

Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.

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References

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