Department News
Origin of Turbulence and its Control in Near-Wall Flows
Seminar Date
2004-01-26
Author
안지영
Date
2004-01-26
Views
1611
1. 제 목 : Origin of Turbulence and its Control in Near-Wall Flows
2. 연 사 : Professor V. V. Kozlov
Leading Research Scientist, Head of Department Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia Also, Visiting Professor at ASERC, Pusan National University
3. 일 시 : 2004년 1월 31일 (토) 오전 10시
4. 장 소 : 301동 1512호 세미나실
5. 내 용 : The presentation is devoted to a review of experimental studies of evolution of disturbances in attached and separated transitional shear layers performed by the author and his research group during last two decades in Russian, Swedish, and German research centers. An emphasis is given to control of transitional flows by different means. For example, several configurations of obstacles causing flow separation were considered and their shapes preferable to prolong laminar regime were suggested. It is also shown that artificially excited disturbances growing in the separation regions can lead to a considerable non-local reconstruction of mean and oscillating flows, which can inhibit the development of turbulence.Tests of riblets in a series of near-wall flows indicated that at certain conditions they are effective means to control streaks – typical structures appeared in transitional boundary layers. These results extend the field of riblet application to transitional flows. Secondary instability is one of the most significant mechanisms of laminar-turbulent transition in flows contaminated with both the streaks and cross-flow vortices. It was experimentally proved that spanwise and wall-normal gradients of streamwise velocity are responsible for the secondary instability. Mechanisms of the instability were investigated as a prerequisite to suggest some techniques of the transition control. Suction of the streaks as well as instability wave canceling by introduction of artificial disturbances with opposite phase were considered and it was found that they are capable to reduce the development of the secondary instability.
6. 문 의 : 기계항공공학부 최 해 천 교수 (☏ 880-8361)
2. 연 사 : Professor V. V. Kozlov
Leading Research Scientist, Head of Department Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia Also, Visiting Professor at ASERC, Pusan National University
3. 일 시 : 2004년 1월 31일 (토) 오전 10시
4. 장 소 : 301동 1512호 세미나실
5. 내 용 : The presentation is devoted to a review of experimental studies of evolution of disturbances in attached and separated transitional shear layers performed by the author and his research group during last two decades in Russian, Swedish, and German research centers. An emphasis is given to control of transitional flows by different means. For example, several configurations of obstacles causing flow separation were considered and their shapes preferable to prolong laminar regime were suggested. It is also shown that artificially excited disturbances growing in the separation regions can lead to a considerable non-local reconstruction of mean and oscillating flows, which can inhibit the development of turbulence.Tests of riblets in a series of near-wall flows indicated that at certain conditions they are effective means to control streaks – typical structures appeared in transitional boundary layers. These results extend the field of riblet application to transitional flows. Secondary instability is one of the most significant mechanisms of laminar-turbulent transition in flows contaminated with both the streaks and cross-flow vortices. It was experimentally proved that spanwise and wall-normal gradients of streamwise velocity are responsible for the secondary instability. Mechanisms of the instability were investigated as a prerequisite to suggest some techniques of the transition control. Suction of the streaks as well as instability wave canceling by introduction of artificial disturbances with opposite phase were considered and it was found that they are capable to reduce the development of the secondary instability.
6. 문 의 : 기계항공공학부 최 해 천 교수 (☏ 880-8361)
