Title: The transition to turbulence: from directed percolation to a discontinuous phase transition
Speaker: Prof. Björn Hof (Institute of Science and Technology Austria)
Time: 2024/08/23 (Fri.) 10:30 a.m - 12:30 p.m
Place: R307, Cosmology Hall, NTU

Abstract
Depending on the type of flow the transition to turbulence can take one of two forms, either turbulence arises from a sequence of instabilities or from the spatial proliferation of transiently chaotic domains, a process analogous to directed percolation. Both scenarios are inherently continuous and hence the transformation from ordered laminar to fully turbulent fluid motion is only accomplished gradually with flow speed. In this talk I will present results of experiments and direct numerical simulations of pipe flow in the presence of body forces (e.g. buoyancy, centrifugal and electromagnetic forces). By attenuating spatial coupling and energy transfer, spatio-temporal intermittency is suppressed in these cases and with forcing amplitude the transition becomes increasingly sharp and eventually discontinuous.