Perturbation threshold and hysteresis associated with the transition to turbulence in sudden expansion pipe flow

•DNS of flow through a circular axisymmetric sudden expansion pipe.•Sub-critical transition to turbulence of the flow with a recirculation region.•Effect of a vortex perturbation at the inlet of the expansion pipe flow.•Threshold amplitude of the perturbation for transition to localised turbulence.•...

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Bibliographic Details
Published in:The International journal of heat and fluid flow 2019-04, Vol.76, p.187-196
Main Authors: Nguyen, Minh Quan, Shadloo, Mostafa Safdari, Hadjadj, Abdellah, Lebon, Benoit, Peixinho, Jorge
Format: Article
Language:English
Subjects:
Direct numerical simulation (DNS)
Engineering Sciences
Fluids mechanics
Instability control
Mechanics
Nonlinear Sciences
Reactive fluid environment
Sudden expansion pipe flow
Transition to turbulence
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Summary:•DNS of flow through a circular axisymmetric sudden expansion pipe.•Sub-critical transition to turbulence of the flow with a recirculation region.•Effect of a vortex perturbation at the inlet of the expansion pipe flow.•Threshold amplitude of the perturbation for transition to localised turbulence.•Hysteresis due to reestablishment of the recirculation region. The complex flow resulting from the laminar-turbulent transition in a sudden expansion pipe flow, with expansion ratio of 1:2, subjected to an inlet parabolic velocity profile and a vortex perturbation, is investigated by means of direct numerical simulations. It is shown that the threshold amplitude for disordered motion is described by a power law scaling, with -3 exponent, as a function of the subcritical Reynolds number. The instability originates from a region of intense shear rate, which results on the flow symmetry breakdown. Above the threshold, several unsteady states are identified using space-time diagrams of the centreline axial velocity fluctuation and their energy. In addition, the simulations show a small hysteresis transition mode due to the reestablishment of the recirculation region in the subcritical range of Reynolds numbers, which depends on: (i) The initial and final quasi-steady states, (ii) the observation time and (iii) the number of intermediate steps taken when increasing and decreasing the Reynolds number.
ISSN:0142-727X
1879-2278
DOI:10.1016/j.ijheatfluidflow.2019.01.018