On wake modulation and interaction features of a pair of dual-step circular cylinders in side-by-side arrangements

Yan, Yuhao; Ji, Chunning; Srinil, Narakorn

doi:10.1063/5.0063885

Cited by 12 publications

(3 citation statements)

References 53 publications

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“…Similar conclusions are drawn for the dual (Ji et al. 2020; Yan, Ji & Srinil 2020, 2021) and multiple (Ayancik et al. 2022) stepped cylinders.…”

Section: Introductionsupporting

confidence: 59%

The flow around a stepped cylinder with turbulent wake and stable shear layer

Massaro,

Peplinski,

Schlatter

2023

J. Fluid Mech.

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The turbulent external flow around a three-dimensional stepped cylinder is studied by means of direct numerical simulations with the adaptive mesh refinement technique. We give a broad perspective of the flow regimes from laminar to turbulent wake at $Re_D=5000$ , which is the highest ever considered for this flow case. In particular, we focus on the intermediate Reynolds number $Re_D=1000$ that reveals a turbulent wake coupled with a stable cylinder shear layer (subcritical regime). This flow shows a junction dynamics similar to the laminar $Re_D=150$ , where no hairpin vortex appears around the edges, and just two horseshoe vortices are visible. A new stable vortex in the form of a ring, which coils around the rear area, is also identified. In the turbulent wake, the presence of three wake cells is pointed out: the large and small cylinder cells together with the modulation region. However, the modulation dynamics varies between the subcritical and turbulent regimes. A time-averaged, three-dimensional set of statistics is computed, and spatially coherent structures are extracted via proper orthogonal decomposition (POD). The POD identifies the (long-debated) connection between the N-cell and the downwash behind the junction. Furthermore, as the Reynolds number increases, the downwash phenomenon becomes less prominent. Eventually, a reduced-order reconstruction with the most energetically relevant modes is defined to explain the wake vortex interactions. This also serves as a valuable starting point for simulating the stepped cylinder wake behaviour within complex frameworks, e.g. fluid–structure interaction.

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“…Similar conclusions are drawn for the dual (Ji et al. 2020; Yan, Ji & Srinil 2020, 2021) and multiple (Ayancik et al. 2022) stepped cylinders.…”

Section: Introductionsupporting

confidence: 59%

The flow around a stepped cylinder with turbulent wake and stable shear layer

Massaro,

Peplinski,

Schlatter

2023

J. Fluid Mech.

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“…In conjunction with the L-L half loop, this zone presents a 'real loop' (N-N) and a 'fake loop' (N-L). Similar findings have been reached in studies involving the multiple-stepped cylinder (Ji et al 2020;Yan, Ji & Srinil 2020, 2021Ayancik et al 2022) and exploring the laminar regime under rotation (Zhao & Zhang 2023). Several experimental campaigns were conducted (Ko & Chan 1992;Morton & Yarusevych 2014b).…”

Section: Introductionsupporting

confidence: 78%

“…Similar findings have been reached in studies involving the multiple-stepped cylinder (Ji et al. 2020; Yan, Ji & Srinil 2020, 2021; Ayancik et al. 2022) and exploring the laminar regime under rotation (Zhao & Zhang 2023).…”

Section: Introductionsupporting

confidence: 74%

Global stability of the flow past a stepped cylinder

Massaro,

Schlatter

2024

J. Fluid Mech.

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We investigate the global instability mechanism of the flow past a three-dimensional stepped cylinder. A comprehensive study is performed for different diameter ratios of the two joined cylinders ( $r=D/d$ ) ranging from $r=1.1$ to $r=4$ . Independently of $r$ , the spectrum of the linearised Navier–Stokes operator reveals a pair of complex conjugate eigenvalues, with Strouhal number $St \approx 0.11$ . The initial transition is triggered by a two-dimensional mechanism of the larger cylinder only, not affected by the presence of the junction and the smaller cylinder ( $Re_{D,cr}\approx 47$ ). The structural sensitivity analysis is used to identify where the instability mechanism acts. The onset of transition is solely localised in the large cylinder wake (L cell), where the wavemaker has two symmetric lobes across the separation bubble. When the Reynolds number increases, a second and a third unstable pair of complex conjugate eigenvalues appears. They are localised in the small cylinder (S) wake and modulation (N) region. For any $r$ , the appearance of unstable eigenmodes resembling the three cells S–N–L in the wake is observed. The nonlinear simulation results support this finding, in contrast with the previous classification of the laminar vortex shedding in direct (L–S) and indirect (L–N–S) modes interaction Lewis & Gharib (Phys. Fluids, vol. 4, 1992, pp. 104–117). This result indicates that each cell undergoes a supercritical Hopf bifurcation for any $r$ . As $r$ approaches $1$ , the modal linear stability results also show an unstable eigenmode in the wake of the small cylinder resembling a new modulation cell, named N2, similar to the N cell but mirrored with respect to the junction plane.

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