Instabilities in the Wake of an Inclined Prolate Spheroid

Andersson, Helge I.; Jiang, Fengjian; Okulov, Valery

doi:10.1007/978-3-319-91494-7_9

Cited by 5 publications

(4 citation statements)

References 96 publications

(96 reference statements)

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“…The local refinement is achieved by means of a multi-level hierarchy, as illustrated in Figure 2. The same computational code was employed in our earlier studies of flow around a 45 ° inclined spheroid at higher Reynolds numbers, as reported by Jiang et al [23], [24] and summarized by Andersson et al [2].…”

Section: Mathematical Modelling and Numerical Methodsmentioning

confidence: 99%

Forces and torques on a prolate spheroid: low-Reynolds-number and attack angle effects

Andersson

Jiang

2018

Acta Mech

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The three-dimensional flow field around a prolate spheroid has been obtained by integration of the full Navier-Stokes equations at Reynolds numbers 0.1, 1.0 and 10. The 6:1 spheroid was embedded in a Cartesian mesh by means of an immersed boundary method. In the low-Re range, due to the dominance of viscous stresses, an exceptionally wide computational domain was required, together with a substantial grid refinement in vicinity of the surface of the immersed spheroid. Flow fields in equatorial and meridional planes were visualized by means of streamlines to illustrate Reynolds number and attack angle effects. Drag and lift forces and torques were computed and compared with the most recent correlation formulas. The largest discrepancies were observed for the moment coefficient whereas the drag coefficient compared reasonably well.

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Section: Mathematical Modelling and Numerical Methodsmentioning

confidence: 99%

Forces and torques on a prolate spheroid: low-Reynolds-number and attack angle effects

Andersson

Jiang

2018

Acta Mech

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“…Each pair stays almost at a fixed position to form an alternating vortex street that can be observed in a cross-sectional plane. The helical vortex pair in an inclined prolate spheroid wake is also asymmetric: when the symmetry of the pair is lost, the wake randomly deflects to one side or the other and never turns back again, resulting in a substantial time-averaged side force acting on the spheroid, as comprehensively reviewed in Andersson, Jiang & Okulov (2019). In both situations, the asymmetric helical vortex pairs are mostly in the streamwise direction rather than in the spanwise direction.…”

Section: The Wake Dynamicsmentioning

confidence: 99%

Turbulent wake behind a concave curved cylinder

2019

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We present a detailed study of the turbulent wake behind a quarter-ring curved cylinder at Reynolds number $Re=3900$ (based on cylinder diameter and incoming flow velocity), by means of direct numerical simulation. The configuration is referred to as a concave curved cylinder with incoming flow aligned with the plane of curvature and towards the inner face of the cylinder. Wake flows behind this configuration are known to be complex, but have so far only been studied at low $Re$. This is the first direct numerical simulation investigation of the turbulent wake behind the concave configuration, from which we reveal new and interesting wake dynamics, and present in-depth physical interpretations. Similar to the low-$Re$ cases, the turbulent wake behind a concave curved cylinder is a multi-regime and multi-frequency flow. However, in addition to the coexisting flow regimes reported at lower $Re$, we observe a new transitional flow regime at $Re=3900$. The flow field in this transitional regime is dominated not by von Kármán-type vortex shedding, but by periodic asymmetric helical vortices. Such vortex pairs exist also in some other wake flows, but are then non-periodic. Inspections reveal that the periodic motion of the asymmetric helical vortices is induced by vortex shedding in its neighbouring oblique shedding regime. The oblique shedding regime is in turn influenced by the transitional regime, resulting in a unified and remarkably low dominating frequency in both flow regimes. Owing to this synchronized frequency, the new wake dynamics in the transitional regime might easily be overlooked. In the near wake, two distinct peaks are observed in the time-averaged axial velocity distribution along the curved cylinder span, while only one peak was observed at lower $Re$. The presence of the additional peak is ascribed to a strong favourable base pressure gradient along the cylinder span. It is noteworthy that the axially directed base flow exceeded the incoming velocity behind a substantial part of the quarter-ring and even persisted upwards along the straight vertical extension. As a by-product of our study, we find that a straight vertical extension of 16 cylinder diameters is required in order to avoid any adverse effects from the upper boundary of the flow domain.

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“…Rhee and Hino [5]). The full history on this topic is properly summarized in Simpson [6] and Andersson et al [7], therefore it will not be repeated here. Nevertheless, it is important to notice that in early research works, emphasis was on the integral body forces and flow details close to the geometry (essentially surface flow, boundary layers, separation, or in special cases the very near wake).…”

Section: Introductionmentioning

confidence: 99%

Near-Wake of an Inclined 6:1 Spheroid at Reynolds Number 4000

et al. 2019

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We describe the flow around a 6:1 prolate spheroid at 45 • inclination angle and Reynolds number 4000 based on the minor axis. Despite that the inflow is uniform and steady, the resulting wake is highly asymmetric and unsteady. Two main vortical structures develop from the shear layers of the spheroid, one being significantly stronger than the other. This asymmetry results in a non-zero sideforce. The forces acting on the spheroid change dramatically from earlier works at Reynolds number 3000. The pressure inside the vortex cores also changed with this moderate increase in Reynolds number. This indicates that the flow is highly transitional.We also document that close to the body, on the side of the weaker vortex, there is a region of negative axial velocity. In this backflow region, the fluid enters from behind the spheroid and travels forward against the inflow and then exits the backflow region through one of the main vortical structures. This backflow has not been described before. We also observe and describe a distinct Kelvin-Helmholtz shear layer instability close to this region.x ax Spheroid major axisx, y, z Cartesian coordinatesThis is a post-print. The Online version is found via. AIAA J. website: https://arc.aiaa.org/doi/full/10.2514/1.J057615 where supplementary animation can also be downloaded.

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Instabilities in the Wake of an Inclined Prolate Spheroid

Cited by 5 publications

References 96 publications

Forces and torques on a prolate spheroid: low-Reynolds-number and attack angle effects

Forces and torques on a prolate spheroid: low-Reynolds-number and attack angle effects

Turbulent wake behind a concave curved cylinder

Near-Wake of an Inclined 6:1 Spheroid at Reynolds Number 4000

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