Abstract
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This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a radius ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at the inner cylinder rotational speed of 0~600rpm. The transitional flow has been examined by the measurement of pressure drops to reveal the relationship between the Reynolds and Rossby numbers considering the skin-friction coefficients. The results show that the skin-friction coefficients have a significant correlation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decreases as the rotational speed increases.
본 연구는 안쪽 실린더가 회전하고 바깥쪽 실린더가 고정된 반경비가 0.52인 동심환형관내 천이유동 특성을 관찰했다. 안쪽실린더가 0~600rpm으로 회전하고 물과 44% 글리세린수용액을 사용한 완전히 발달된 유동에서 압력강하와 표면마찰계수를 측정하였다. 천이유동은 표면마찰계수에 대한 레이놀즈수와 로스비수 관계를 나타내기 위해 압력강하를 측정하였다. 결과는 단지 층류영역에서 로스비수에 대해 표면마찰계수가 중요한 관계를 보인다. 천이의 발생은 레이놀즈수에 관해 압력손실과 표면마찰계수의 구배변화에 의해 조사했다. 회전에 의한 표면마찰계수의 증가율은 층류영역에서는 균일하고 반면에 천이영역에서는 갑자가 감소하며 난류영역으로 갈수록 점차적으로 감소한다. 결과적으로 임계레이놀즈수는 회전속도가 증가함에 따라 감소함을 알 수 있다.
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- Publisher :The Korean Society of Mineral and Energy Resources Engineers
- Publisher(Ko) :한국자원공학회
- Journal Title :Journal of the Korean Society for Geosystem Engineering
- Journal Title(Ko) :한국지구시스템공학회지
- Volume : 43
- No :4
- Pages :293-300
Journal of the Korean Society of Mineral and Energy Resources Engineers
