Journal of the Korean Society of Marine Environment & Safety (해양환경안전학회지)

The Korean Society of Marine Environment and safety (해양환경안전학회)
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Grid Tests for Large Eddy Simulation of Transitional Flows around Turbulence Stimulators

난류 촉진기 주위 천이 유동의 대형 와 모사를 위한 격자 테스트

  • Lee, Sang Bong (Department of Naval Architecture and Offshore Engineering, Dong-A University) ;
  • Park, Dong Woo (Department of Naval Architecture and Ocean Engineering, Tongmyong University) ;
  • Paik, Kwang-Jun (Department of Naval Architecture and Ocean Engineering, Inha University)
  • 이상봉 (동아대학교 조선해양플랜트공학과) ;
  • 박동우 (동명대학교 조선해양공학과) ;
  • 백광준 (인하대학교 조선해양공학과)
  • Received : 2017.01.10
  • Accepted : 2017.02.25
  • Published : 2017.02.28
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Abstract

Large eddy simulations of transitional flows around a stud installed on a flat plate have been performed to investigate an influence of grid resolution on turbulence stimulation by the stud. Because streamwise vortical structures generated by the stud played an important role in turbulence stimulation of boundary layer, streamwise vorticity was compared in the wake region behind the stud when the number of grids increased or decreased by a ratio of ${\sqrt{2}}$ in streamwise, wall-normal and spanwise directions respectively. The streamwise vorticity was shown to be mainly affected by spanwise grid resolution (${\Delta}z^+$) rather than streamwise and wall-normal grid resolution. In a viewpoint of numerical efficiency as well as physical resolution, ${\Delta}x^+{_{min}}=7.6$, ${\Delta}x^+{_{max}}=41$, ${\Delta}y^+{_{wall}}=0.25$ and ${\Delta}z^+=7.6$ was found to be desirable. Once a grid resolution was determined in each direction, a grid verification was carried out by increasing or decreasing the grid resolution y a ratio of ${\sqrt{2}}$ in all directions. The grid uncertainties of pressure and drag coefficients were 21.6 % and 2.8 % while the corrected uncertainties were 2 % and 0.3 %, respectively.

평판에 설치된 스터드 주위의 천이 유동에 있어 격자 크기의 영향을 알기 위해 대형 와 모사를 수행하였다. 스터드에서 야기되는 주 유동 방향의 와 구조가 스터드 후류의 천이에 미치는 영향이 매우 크기 때문에 주 유동 방향, 벽면 수직 방향 그리고 횡 방향으로 격자 크기를 ${\sqrt{2}}$ 배씩 증가시키거나 감소시키면서 스터드 후류에서 주 유동 방향의 와도를 비교하였다. 그 결과 스터드 후류에서 발달하는 주 유동 방향의 와도는 횡 방향 격자 크기에 매우 큰 영향을 받는 것을 알 수 있었으며, 이러한 결과를 바탕으로 ${\Delta}x^+{_{min}}=7.6$, ${\Delta}x^+{_{max}}=41$, ${\Delta}y^+{_{wall}}=0.25$ and ${\Delta}z^+=7.6$의 격자 크기를 결정하였다. 이러한 격자 구성에 있어 모든 방향으로 격자 크기를 동시에 ${\sqrt{2}}$ 배씩 증가시키거나 감소시키면서 스터드에 작용하는 힘의 변화를 비교하여 격자 검증을 실시한 결과 평균 압력 계수와 항력 계수의 비보정 불확실성이 각각 21.6 %와 2.8 % 정도로 추정되었으며, 보정 불확실성은 각각 2 %와 0.3 %로 추정되었다.

Keywords

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