Combined Effect of Short Roughness Strip and Concentrated Wall Suction on Coherent Structure in a Turbulent Boundary Layer

2008 ◽  
Vol 35 (6) ◽  
pp. 581-593
Author(s):  
M. O. Oyewola ◽  
A. A. Adesina
2019 ◽  
Vol 32 (11) ◽  
pp. 2433-2442 ◽  
Author(s):  
Guangyao CUI ◽  
Chong PAN ◽  
Di WU ◽  
Qingqing YE ◽  
Jinjun WANG

2007 ◽  
Vol 586 ◽  
pp. 371-396 ◽  
Author(s):  
MASAHITO ASAI ◽  
YASUFUMI KONISHI ◽  
YUKI OIZUMI ◽  
MICHIO NISHIOKA

Two-dimensional local wall suction is applied to a fully developed turbulent boundary layer such that near-wall turbulence structures are completely sucked out, but most of the turbulent vortices in the original outer layer can survive the suction and cause the resulting laminar flow to undergo re-transition. This enables us to observe and clarify the whole process by which the suction-surviving strong vortical motions give rise to near-wall low-speed streaks and eventually generate wall turbulence. Hot-wire and particle image velocimetry (PIV) measurements show that low-frequency velocity fluctuations, which are markedly suppressed near the wall by the local wall suction, soon start to grow downstream of the suction. The growth of low-frequency fluctuations is algebraic. This characterizes the streak growth caused by the suction-surviving turbulent vortices. The low-speed streaks obtain almost the same spanwise spacing as that of the original turbulent boundary layer without the suction even in the initial stage of the streak development. This indicates that the suction-surviving turbulent vortices are efficient in exciting the necessary ingredients for the wall turbulence, namely, low-speed streaks of the correct scale. After attaining near-saturation, the low-speed streaks soon undergo sinuous instability to lead to re-transition. Flow visualization shows that the streak instability and its subsequent breakdown occur at random in space and time in spite of the spanwise arrangement of streaks being almost periodic. Even under the high-intensity turbulence conditions, the sinuous instability amplifies disturbances of almost the same wavelength as predicted from the linear stability theory, though the actual growth is in the form of a wave packet with not more than two waves. It should be emphasized that the mean velocity develops the log-law profile as the streak breakdown proceeds. The transient growth and eventual breakdown of low-speed streaks are also discussed in connection with the critical condition for the wall-turbulence generation.


2001 ◽  
Vol II.01.1 (0) ◽  
pp. 219-220
Author(s):  
Yasuhiko SAKAI ◽  
Takehiro KUSHIDA ◽  
Koji OHTA ◽  
Kazushige YOSHIDA ◽  
Hirokazu ITO

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