A Study on the Effect of Large Coherent Structures to the Skin Friction by POD Analysis

적합직교분해(POD)기법을 사용한 난류 응집구조 거동에 관한 연구

  • Shin, Seong-Yun (Department of Naval Architecture and Ocean Engineering, Pusan National University) ;
  • Jung, Kwang-Hyo (Department of Naval Architecture and Ocean Engineering, Pusan National University) ;
  • Kang, Yong-Duck (Department of Naval Architecture and Ocean Engineering, Dong-Eui University) ;
  • Suh, Sung-Bu (Department of Naval Architecture and Ocean Engineering, Dong-Eui University) ;
  • Kim, Jin (Advanced Ship Research Division, Korea Research Institute of Ships & Ocean Engineering) ;
  • An, Nam-Hyun (Department of Naval Architecture and Ocean Engineering, Koje College)
  • 신성윤 (부산대학교 조선해양공학과) ;
  • 정광효 (부산대학교 조선해양공학과) ;
  • 강용덕 (동의대학교 조선해양공학과) ;
  • 서성부 (동의대학교 조선해양공학과) ;
  • 김진 (선박해양플랜트연구소 미래선박연구부) ;
  • 안남현 (거제대학교 조선해양공학과)
  • Received : 2017.03.29
  • Accepted : 2017.09.08
  • Published : 2017.10.20


An experimental study in a recirculating water channel was carried out to investigate the effect of large coherent structures to the skin friction on a flat plate. Particle Image Velocimetry (PIV) technique was used to quantify characteristic features of coherent structures growing to the boundary layer. In the PIV measurement, it is difficult to calculate the friction velocity near the wall region due to laser deflection and uncertainty so that Clauser fitting method at the logarithmic region was adopted to compute the friction velocity and compared with the one directly measured by the dynamometer. With changing the free-stream velocity from 0.5 m/s to 1.0 m/s, the activity of coherent structures in the logarithmic region was increased over three times in terms of Reynolds stress. The flow field was separated by Variable Interval Time Averaging (VITA) technique into the weak and the strong structure case depending on the existence large coherent structures in order to validate its effectiveness. The stream-wise velocity fluctuation was scanned through at the boundary thickness whether it had a large deviation from background flow. With coherent structures connected from near-wall to the boundary layer, mean wall shear stress was higher than that of weak structure case. Proper Orthogonal Decomposition (POD) analysis was also applied to compare the energy budget between them at each free-stream velocity.


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