The production of turbulence near a wall is the governing mechanism of the turbulent drag from external flow around bodies and in internal flows involving turbulence. The pocket is closely associated with the occurrence of the large Reynolds stress producing motions, and therefore implicitly involved with the turbulence production process. Within the wall region, hot-wire measurements show that a strong vortex forms within the pockets. This vortex is the rearrangement of existing sublayer vorticity and its amplification. The work in this area has been applied to the prediction and reduction of drag. The study is focused on the time scale of the pockets. The relationship between pocket time scale and modified wall has been found. By changing the upstream boundary condition at the wall the time scale of pockets were increased.

ABSTRACT
1. 서 론
2. 실험장치 및 방법
    2.1 속도 데이터 취득 시스템
    2.2 고속 사진촬영 시스템
    2.3 가시화 마커 분사
    2.4 밝은 조명
    2.5 저속 풍동
    2.6 벽면의 형상 변화
    2.7 평균속도 프로파일 데이터 처리 기술
    2.8 가시화 데이터
3. 결과 및 고찰
    3.1 평균속도 프로파일 데이터
    3.2 포켓 time scale
4. 결 론
References

• 유성출(Dept. of mechanical & automotive Engr., Halla University) | Seoung-Chool Yoo Corresponding Author