TY  - JOUR
A1  - Pratt, Jane
A1  - Busse, Angela
A1  - Mueller, W-C
A1  - Watkins, Nikolas W.
A1  - Chapman, Sandra C.
T1  - Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection
JF  - New journal of physics : the open-access journal for physics
N2  - We investigate the utility of the convex hull of many Lagrangian tracers to analyze transport properties of turbulent flows with different anisotropy. In direct numerical simulations of statistically homogeneous and stationary Navier-Stokes turbulence, neutral fluid Boussinesq convection, and MHD Boussinesq convection a comparison with Lagrangian pair dispersion shows that convex hull statistics capture the asymptotic dispersive behavior of a large group of passive tracer particles. Moreover, convex hull analysis provides additional information on the sub-ensemble of tracers that on average disperse most efficiently in the form of extreme value statistics and flow anisotropy via the geometric properties of the convex hulls. We use the convex hull surface geometry to examine the anisotropy that occurs in turbulent convection. Applying extreme value theory, we show that the maximal square extensions of convex hull vertices are well described by a classic extreme value distribution, the Gumbel distribution. During turbulent convection, intermittent convective plumes grow and accelerate the dispersion of Lagrangian tracers. Convex hull analysis yields information that supplements standard Lagrangian analysis of coherent turbulent structures and their influence on the global statistics of the flow.
KW  - turbulence
KW  - magnetohydrodynamics
KW  - Lagrangian statistics
KW  - magnetoconvection
KW  - turbulent transport
Y1  - 2017
U6  - https://doi.org/10.1088/1367-2630/aa6fe8
SN  - 1367-2630
VL  - 19
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Feudel, Fred
A1  - Tuckerman, L. S.
A1  - Gellert, Marcus
A1  - Seehafer, Norbert
T1  - Bifurcations of rotating waves in rotating spherical shell convection
JF  - Physical Review  E
N2  - The dynamics and bifurcations of convective waves in rotating and buoyancy-driven spherical Rayleigh-Benard convection are investigated numerically. The solution branches that arise as rotating waves (RWs) are traced by means of path-following methods, by varying the Rayleigh number as a control parameter for different rotation rates. The dependence of the azimuthal drift frequency of the RWs on the Ekman and Rayleigh numbers is determined and discussed. The influence of the rotation rate on the generation and stability of secondary branches is demonstrated. Multistability is typical in the parameter range considered.
KW  - nonsymmetric linear-systems
KW  - thermal-convection
KW  - fluid shells
KW  - hopf-bifurcation
KW  - onset
KW  - magnetoconvection
KW  - number
KW  - flow
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.053015
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 5
PB  - American Physical Society
CY  - Woodbury
ER  -