期刊
JOURNAL OF FLUID MECHANICS
卷 728, 期 -, 页码 306-339出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2013.287
关键词
boundary layers; instability; transition to turbulence
资金
- European Commission Seventh Framework Programme under a Marie Curie Intra-European Fellowship
- UK Engineering and Physical Sciences Research Council (EPSRC)
- Engineering and Physical Sciences Research Council [EP/K503381/1, EP/G069581/1] Funding Source: researchfish
- EPSRC [EP/G069581/1] Funding Source: UKRI
Statistical analysis of transitional boundary layers in pressure gradients is performed using the flow fields from direct numerical simulations of bypass transition. Laminar-turbulent discrimination separates the streaky laminar flow from turbulent regions. Individual streaks are identified and tracked in the flow field in order to obtain statistics of the amplitude of the streak population. An extreme value model is proposed for the distribution of streak amplitudes. It is also possible to differentiate those streaks which break down into turbulent spots from innocuous events. It is shown that turbulence onset is due to high-amplitude streaks, with streamwise perturbation velocity exceeding 20% of the free stream speed. The resulting turbulent spots are tracked downstream. The current analysis allows for the measurement of the lateral spreading angles of individual spots and their spatial extent and volumes. It is demonstrated that the volumetric growth rate of turbulent spots is insensitive to pressure gradient.
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