Small-scale dynamics is the spirit of turbulence physics. It delivers complex mechanisms when turbulence is purely sustained by buoyancy. This takes place in Rayleigh-Bénard convection (RBC). Most of the existing RBC dynamics is ruled by hard turbulent regime and a deep understanding of small scale dynamics with its relevant nonlinearities, is still unsatis¿ed. To do so, the evolution of QG =-1/2tr(G2) and RG =-1/3tr(G3), invariants of the velocity gradient tensor, G = Gradu u u, in their phase space{QG,RG}, were studied and reported in Dabbagh et al. [1] using DNS of RBC. In the present work, we expand this 2D {QG,RG} evolution to 3D by decomposing RG into its strain production RS = -1/3tr(S3) andenstrophyproductiontr(¿2S) =RS-RG terms, where S and ¿ aretherate-of-strainandrate-of-rotation tensors, respectively. In the {QG,RS,RS-RG} space, the ¿ow topology in a Lagrangian evolution is changing by the conditionalmeantrajectories(CMTs){DQG/Dt,DRS/Dt,D(RS-RG)/Dt}. Usingthedatasetin[1],andfromFigure46: anidenti¿edcyclicalstartoftrajectoriesisdistinguishedinareasofvortex-stretchingRS-RG >0andRS >0inthestrain dominated slots (QG < 0), which becomes stronger and longer expanded at Rayleigh number Ra = 1010. Afterwards, the trajectories move downwards (QG << 0) in areas of vortex-compression RS-RG < 0 and RS > 0, that also become more diverging at Ra = 1010 as a result of the self-ampli¿ed straining [1]. This is followed by rising trajectories upwards (QG > 0) to continue performing the typical planner {QG,RG} cyclical behaviour [1], next to RS = 0, and decaying towards the origin. DNS at Ra = 1011 is currently being computed on the MareNostrum supercomputer [2]. Results will be presented during the conference.

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