Periodically driven Taylor–Couette turbulence

Abstract

We study periodically driven Taylor-Couette turbulence, i.e. the flow confined between two concentric, independently rotating cylinders. Here, the inner cylinder is driven sinusoidally while the outer cylinder is kept at rest (time-averaged Reynolds number is Re i = 5 × 10 5 ). Using particle image velocimetry (PIV), we measure the velocity over a wide range of modulation periods, corresponding to a change in Womersley number in the range 15 Wo 114. To understand how the flow responds to a given modulation, we calculate the phase delay and amplitude response of the azimuthal velocity.In agreement with earlier theoretical and numerical work, we find that for large modulation periods the system follows the given modulation of the driving, i.e. the system behaves quasi-stationary. For smaller modulation periods, the flow cannot follow the modulation, and the flow velocity responds with a phase delay and a smaller amplitude response to the given modulation. If we compare our results with numerical and theoretical results for the laminar case, we find that the scalings of the phase delay and the amplitude response are similar. However, the local response in the bulk of the flow is independent of the distance to the modulated boundary. Apparently, the turbulent mixing is strong enough to prevent the flow from having radius-dependent responses to the given modulation.

The energy cascade as the origin of intense events in small-scale turbulence

“…The dissipation signal fluctuates around its mean in time scales comparable to the integral time scale, mirroring the fluctuations of the surrogate dissipation, which occur earlier. This time lag reflects the large-scale modulation of the small scales, which is a general feature of turbulent flows and has been observed previously in homogeneous flows (Kuczaj, Geurts & Lohse 2006;Chien, Blum & Voth 2013), wall-bounded flows (Hutchins & Marusic 2007;Mathis, Hutchins & Marusic 2009;Verschoof et al 2018), and shear flows (Fiscaletti et al 2016;Lalescu & Wilczek 2021). The time advancement of the surrogate dissipation with respect to the dissipation reflects the propagation of large-scale fluctuations down the energy cascade.…”

“…This time lag reflects the large-scale modulation of the small scales, which is a general feature of turbulent flows and has been observed previously in homogeneous flows (Kuczaj, Geurts & Lohse 2006; Chien, Blum & Voth 2013), wall-bounded flows (Hutchins & Marusic 2007; Mathis, Hutchins & Marusic 2009; Verschoof et al. 2018), and shear flows (Fiscaletti et al. 2016; Lalescu & Wilczek 2021).…”

On the ridge of instability in ferrofluidic Couette flow via alternating magnetic field

“…The effect of time-periodic forcing in TCS has been investigated in numerous works [4][5][6][7][8][9][10][11] . Such a forcing can be realized by (axial or azimuthal) oscillation of one or both cylinders, further by pulsation of axial imposed flow or radial through flow, with the latter requiring porous cylinder walls.…”

A direct comparison of pulsatile and non-pulsatile rough-wall turbulent pipe flow

“…Non-pulsatile rough-wall turbulent pipe flow has been studied for many decades (Nikuradse 1933;Shockling, Allen & Smits 2006;Chan et al 2015). Likewise, † Email address for correspondence: tom.jelly@unimelb.edu.au pulsatile smooth-wall pipe flow continues to receive attention across a range of forcing conditions (Manna, Vacca & Verzicco 2012;Papadopoulos & Vouros 2016;Cheng et al 2020), along with smooth-wall pulsatile turbulent channel flow (Scotti & Piomelli 2001;Weng, Boij & Hanifi 2016), oscillatory open-channel flow (Kaptein et al 2019) and periodically forced Taylor-Couette turbulence (Verschoof et al 2018). Pulsatile rough-wall turbulent channel flow has also been examined at three different forcing frequencies in past work by Bhaganagar (2008) using direct numerical simulation (DNS).…”