An almost subharmonic instability in the flow past rectangular cylinders

Chiarini, Alessandro; Quadrio, Maurizio; Auteri, Franco

doi:10.1017/jfm.2022.712

Cited by 4 publications

(4 citation statements)

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“…Although these two flow configurations are different, the hairpin vortices in both flows are evolved from KH vortices. Furthermore, the LE vortices composed of multiple hairpin vortices appear more irregular than those observed at lower Reynolds numbers in the studies of Hourigan et al (2001) and Chiarini et al (2022b). It should be noted that the scale of hairpin vortices appears larger than the results reported by Cimarelli et al (2018b), and Chiarini et al (2022a), which can be attributed to the higher Reynolds numbers employed in their investigations.…”

Section: Instantaneous Vortical Structures and Mean Flow Statisticsmentioning

confidence: 66%

“…(2001) and Chiarini et al. (2022 b ). It should be noted that the scale of hairpin vortices appears larger than the results reported by Cimarelli et al.…”

Section: Resultsmentioning

confidence: 96%

“…Although the spanwise wake shedding modes are similar to those observed for a circular cylinder (referred to as ‘mode A’ and ‘mode B’) (Williamson 1988), the spanwise wavelengths are larger due to the thicker boundary layers near the TE, which lead to more diffused vortices. In a recent study by Chiarini, Quadrio & Auteri (2022 b ), the three-dimensional instability of flow around a rectangular cylinder with an aspect ratio of 5 was investigated using Floquet analysis and DNS. A new quasisubharmonic (QS) unstable mode was discovered, which becomes unstable at approximately with a spanwise wavelength .…”

Section: Introductionmentioning

confidence: 99%

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Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

Li,

Wang,

Qiu

et al. 2024

J. Fluid Mech.

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The numerical investigation focuses on the flow patterns around a rectangular cylinder with three aspect ratios ( $L/D=5$ , $10$ , $15$ ) at a Reynolds number of $1000$ . The study delves into the dynamics of vortices, their associated frequencies, the evolution of the boundary layer and the decay of the wake. Kelvin–Helmholtz (KH) vortices originate from the leading edge (LE) shear layer and transform into hairpin vortices. Specifically, at $L/D=5$ , three KH vortices merge into a single LE vortex. However, at $L/D=10$ and $15$ , two KH vortices combine to form a LE vortex, with the rapid formation of hairpin vortex packets. A fractional harmonic arises due to feedback from the split LE shear layer moving upstream, triggering interaction with the reverse flow. Trailing edge (TE) vortices shed, creating a Kármán-like street in the wake. The intensity of wake oscillation at $L/D=5$ surpasses that in the other two cases. Boundary layer transition occurs after the saturation of disturbance energy for $L/D=10$ and $15$ , but not for $L/D=5$ . The low-frequency disturbances are selected to generate streaks inside the boundary layer. The TE vortex shedding induces the formation of a favourable pressure gradient, accelerating the flow and fostering boundary layer relaminarization. The self-similarity of the velocity defect is observed in all three wakes, accompanied by the decay of disturbance energy. Importantly, the decrease in the shedding frequency of LE (TE) vortices significantly contributes to the overall decay of disturbance energy. This comprehensive exploration provides insights into complex flow phenomena and their underlying dynamics.

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Section: Instantaneous Vortical Structures and Mean Flow Statisticsmentioning

confidence: 66%

“…(2001) and Chiarini et al. (2022 b ). It should be noted that the scale of hairpin vortices appears larger than the results reported by Cimarelli et al.…”

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

Li,

Wang,

Qiu

et al. 2024

J. Fluid Mech.

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“…The vortex shedding from the LE corners also influences the secondary instability of the flow leading to three-dimensionality. Unlike for circular and short square cylinders and for elongated cylinders with elliptic leading edge (Robichaux, Balachandar & Vanka 1999; Ryan, Thompson & Hourigan 2005), for elongated rectangular cylinders, the onset of three-dimensionality is due to an almost subharmonic mode triggered by the non-viscous interaction of the LE vortices simultaneously placed over the longitudinal side of the cylinder (Chiarini, Quadrio & Auteri 2022 a ).…”

Section: Introductionmentioning

confidence: 99%

Linear global and asymptotic stability analysis of the flow past rectangular cylinders moving along a wall

Chiarini

Auteri

2023

J. Fluid Mech.

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The primary instability of the steady two-dimensional flow past rectangular cylinders moving parallel to a solid wall is studied, as a function of the cylinder length-to-thickness aspect ratio ${A{\kern-4pt}R} =L/D$ and the dimensionless distance from the wall $g=G/D$ . For all ${A{\kern-4pt}R}$ , two kinds of primary instability are found: a Hopf bifurcation leading to an unsteady two-dimensional flow for $g \ge 0.5$ , and a regular bifurcation leading to a steady three-dimensional flow for $g < 0.5$ . The critical Reynolds number $Re_{c,2\text{-}D}$ of the Hopf bifurcation ( $Re=U_\infty D/\nu$ , where $U_\infty$ is the free stream velocity, $D$ the cylinder thickness and $\nu$ the kinematic viscosity) changes with the gap height and the aspect ratio. For ${A{\kern-4pt}R} \le 1$ , $Re_{c,2\text{-}D}$ increases monotonically when the gap height is reduced. For ${A{\kern-4pt}R} >1$ , $Re_{c,2\text{-}D}$ decreases when the gap is reduced until $g \approx 1.5$ , and then it increases. The critical Reynolds number $Re_{c,3\text{-}D}$ of the three-dimensional regular bifurcation decreases monotonically for all ${A{\kern-4pt}R}$ , when the gap height is reduced below $g < 0.5$ . For small gaps, $g < 0.5$ , the hyperbolic/elliptic/centrifugal character of the regular instability is investigated by means of a short-wavelength approximation considering pressureless inviscid modes. For elongated cylinders, ${A{\kern-4pt}R} > 3$ , the closed streamline related to the maximum growth rate is located within the top recirculating region of the wake, and includes the flow region with maximum structural sensitivity; the asymptotic analysis is in very good agreement with the global stability analysis, assessing the inviscid character of the instability. For cylinders with $AR \leq 3$ , however, the local analysis fails to predict the three-dimensional regular bifurcation.

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Turbulent transports in the flow around a rectangular cylinder with different aspect ratios

Li,

Wang,

Qiu

et al. 2024

Ocean Engineering

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An almost subharmonic instability in the flow past rectangular cylinders

Cited by 4 publications

References 59 publications

Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

Vortex dynamics and boundary layer transition in flow around a rectangular cylinder with different aspect ratios at medium Reynolds number

Linear global and asymptotic stability analysis of the flow past rectangular cylinders moving along a wall

Turbulent transports in the flow around a rectangular cylinder with different aspect ratios

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