Role of critical points of the skin friction field in formation of plumes in thermal convection
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In: Physical Review E, Vol. 92, No. 4, 043006, 06.10.2015.
Research output: Journal contributions › Journal articles › Research › peer-review
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TY - JOUR
T1 - Role of critical points of the skin friction field in formation of plumes in thermal convection
AU - Bandaru, Vinodh
AU - Kolchinskaya, Anastasiya
AU - Padberg-Gehle, Kathrin
AU - Schumacher, Jörg
N1 - Publisher Copyright: © 2015 American Physical Society.
PY - 2015/10/6
Y1 - 2015/10/6
N2 - The dynamics in the thin boundary layers of temperature and velocity is the key to a deeper understanding of turbulent transport of heat and momentum in thermal convection. The velocity gradient at the hot and cold plates of a Rayleigh-Bénard convection cell forms the two-dimensional skin friction field and is related to the formation of thermal plumes in the respective boundary layers. Our analysis is based on a direct numerical simulation of Rayleigh-Bénard convection in a closed cylindrical cell of aspect ratio Γ=1 and focused on the critical points of the skin friction field. We identify triplets of critical points, which are composed of two unstable nodes and a saddle between them, as the characteristic building block of the skin friction field. Isolated triplets as well as networks of triplets are detected. The majority of the ridges of linelike thermal plumes coincide with the unstable manifolds of the saddles. From a dynamical Lagrangian perspective, thermal plumes are formed together with an attractive hyperbolic Lagrangian coherent structure of the skin friction field. We also discuss the differences from the skin friction field in turbulent channel flows from the perspective of the Poincaré-Hopf index theorem for two-dimensional vector fields.
AB - The dynamics in the thin boundary layers of temperature and velocity is the key to a deeper understanding of turbulent transport of heat and momentum in thermal convection. The velocity gradient at the hot and cold plates of a Rayleigh-Bénard convection cell forms the two-dimensional skin friction field and is related to the formation of thermal plumes in the respective boundary layers. Our analysis is based on a direct numerical simulation of Rayleigh-Bénard convection in a closed cylindrical cell of aspect ratio Γ=1 and focused on the critical points of the skin friction field. We identify triplets of critical points, which are composed of two unstable nodes and a saddle between them, as the characteristic building block of the skin friction field. Isolated triplets as well as networks of triplets are detected. The majority of the ridges of linelike thermal plumes coincide with the unstable manifolds of the saddles. From a dynamical Lagrangian perspective, thermal plumes are formed together with an attractive hyperbolic Lagrangian coherent structure of the skin friction field. We also discuss the differences from the skin friction field in turbulent channel flows from the perspective of the Poincaré-Hopf index theorem for two-dimensional vector fields.
KW - Mathematics
UR - http://www.scopus.com/inward/record.url?scp=84944753339&partnerID=8YFLogxK
UR - https://www.mendeley.com/catalogue/56fe5abe-979f-37b8-a5f8-313bf3b34f74/
U2 - 10.1103/PhysRevE.92.043006
DO - 10.1103/PhysRevE.92.043006
M3 - Journal articles
C2 - 26565331
VL - 92
JO - Physical Review E
JF - Physical Review E
SN - 2470-0045
IS - 4
M1 - 043006
ER -