## Lagrangian heat transport in turbulent three-dimensional convection

Publikation: Beiträge in Zeitschriften › Zeitschriftenaufsätze › Forschung › begutachtet

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**Lagrangian heat transport in turbulent three-dimensional convection.** / Vieweg, Philipp P.; Schneide, Christiane; Padberg-Gehle, Kathrin et al.

Publikation: Beiträge in Zeitschriften › Zeitschriftenaufsätze › Forschung › begutachtet

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*Physical Review Fluids*, Jg. 6, Nr. 4, L041501. https://doi.org/10.1103/PhysRevFluids.6.L041501

### APA

*Physical Review Fluids*,

*6*(4), [L041501]. https://doi.org/10.1103/PhysRevFluids.6.L041501

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TY - JOUR

T1 - Lagrangian heat transport in turbulent three-dimensional convection

AU - Vieweg, Philipp P.

AU - Schneide, Christiane

AU - Padberg-Gehle, Kathrin

AU - Schumacher, Jörg

PY - 2021/4/1

Y1 - 2021/4/1

N2 - Spatial regions that do not mix effectively with their surroundings in fully turbulent three-dimensional Rayleigh-Bénard convection are identified by clusters of Lagrangian trajectory segments. By monitoring a locally defined Nusselt number along these trajectories it is quantified that these Lagrangian coherent sets, which are indicated by the tracer clouds in the figures, contribute significantly less to the global heat transport than their spatial complement where thermal plumes rise and fall.Spatial regions that do not mix effectively with their surroundings and, thus, contribute less to the heat transport in fully turbulent three-dimensional Rayleigh-Bénard flows are identified by Lagrangian trajectories that stay together for a longer time. These trajectories probe Lagrangian coherent sets (CSs) which we investigate here in direct numerical simulations in convection cells with a square cross section of aspect ratio Γ=16, Rayleigh number Ra=105, and Prandtl numbers Pr=0.1,0.7, and 7. The analysis is based on N=524288 Lagrangian tracer particles which are advected in the time-dependent flow. Clusters of trajectories are identified by a graph Laplacian with a diffusion kernel, which quantifies the connectivity of trajectory segments, and a subsequent sparse eigenbasis approximation (SEBA) for cluster detection. The combination of graph Laplacian and SEBA leads to a significantly improved cluster identification that is compared with the large-scale patterns in the Eulerian frame of reference. We show that the detected CSs contribute by a third less to the global turbulent heat transport for all investigated Prandtl numbers compared to the trajectories in the spatial complement. This is realized by monitoring Nusselt numbers along the tracer trajectory ensembles, a dimensionless local measure of heat transfer.

AB - Spatial regions that do not mix effectively with their surroundings in fully turbulent three-dimensional Rayleigh-Bénard convection are identified by clusters of Lagrangian trajectory segments. By monitoring a locally defined Nusselt number along these trajectories it is quantified that these Lagrangian coherent sets, which are indicated by the tracer clouds in the figures, contribute significantly less to the global heat transport than their spatial complement where thermal plumes rise and fall.Spatial regions that do not mix effectively with their surroundings and, thus, contribute less to the heat transport in fully turbulent three-dimensional Rayleigh-Bénard flows are identified by Lagrangian trajectories that stay together for a longer time. These trajectories probe Lagrangian coherent sets (CSs) which we investigate here in direct numerical simulations in convection cells with a square cross section of aspect ratio Γ=16, Rayleigh number Ra=105, and Prandtl numbers Pr=0.1,0.7, and 7. The analysis is based on N=524288 Lagrangian tracer particles which are advected in the time-dependent flow. Clusters of trajectories are identified by a graph Laplacian with a diffusion kernel, which quantifies the connectivity of trajectory segments, and a subsequent sparse eigenbasis approximation (SEBA) for cluster detection. The combination of graph Laplacian and SEBA leads to a significantly improved cluster identification that is compared with the large-scale patterns in the Eulerian frame of reference. We show that the detected CSs contribute by a third less to the global turbulent heat transport for all investigated Prandtl numbers compared to the trajectories in the spatial complement. This is realized by monitoring Nusselt numbers along the tracer trajectory ensembles, a dimensionless local measure of heat transfer.

KW - Mathematics

KW - research areas

KW - Rayleigh-Bénard convection

KW - techniques

KW - Lagrangian particle tracking

KW - fluid dynamics

UR - http://www.scopus.com/inward/record.url?scp=85104845672&partnerID=8YFLogxK

U2 - 10.1103/PhysRevFluids.6.L041501

DO - 10.1103/PhysRevFluids.6.L041501

M3 - Journal articles

VL - 6

JO - Physical Review Fluids

JF - Physical Review Fluids

SN - 2469-990X

IS - 4

M1 - L041501

ER -