On association of lift generation, wake topology and kinematics of oscillating foils

Verma, Suyash; Khalid, Muhammad Saif Ullah; Hemmati, Arman

doi:10.1177/17568293211073959

Cited by 4 publications

(6 citation statements)

References 34 publications

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“…Data accessibility. The relevant video files, data, open source numerical solver and related documentation are provided in the electronic supplementary material [55].…”

Section: Discussionmentioning

confidence: 99%

“…The continuity and Navier-Stokes equations were solved directly using OpenFOAM, which is a numerical package based on the finite-volume method. It is extensively used for simulating wake dynamics of oscillating foils and panels [17,33,38,41,[43][44][45][46][47][48]. The oscillatory foil dynamics was modelled using the Overset Grid Assembly (OGA) method, based on a stationary background grid and a moving overset grid that were merged for the simulation [49].…”

Section: (A) Numerical Detailsmentioning

confidence: 99%

“…This leads to changes in AT relative to a fixed ho/c (=0.25) and θ=false(10∘false) [33]. ϕ below 225∘ are suggestive of a heave-dominated kinematics, based on the relatively higher hL compared with AT [38]. At ϕ≥225∘, the oscillating foil kinematics starts transitioning towards pitch-dominated motion settings [38].…”

Section: Problem Descriptionmentioning

confidence: 99%

“…ϕ below 225∘ are suggestive of a heave-dominated kinematics, based on the relatively higher hL compared with AT [38]. At ϕ≥225∘, the oscillating foil kinematics starts transitioning towards pitch-dominated motion settings [38]. On account of variation in ϕ and AT, Strouhal number (StA=2fAT/Unormal∞) is varied in the range specified earlier, where the maximum StA corresponds to both ϕ=90∘ and 270∘, while the least StA is observed at ϕ=180∘ [33].…”

Section: Problem Descriptionmentioning

confidence: 99%

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On the association of kinematics, spanwise instability and growth of secondary vortex structures in the wake of oscillating foils

Verma,

Khalid,

Hemmati

2023

Proc. R. Soc. A.

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Three-dimensional wake of an oscillating foil with combined heaving and pitching motion is numerically evaluated at a range of chord-based Strouhal number ( 0.32 ≤ S t c ≤ 0.56 ) and phase offset ( 90 ∘ ≤ ϕ ≤ 270 ∘ ) at R e = 8000 . The changes in ϕ and S t c reflect a unique route of transition in mechanisms that govern the origin of spanwise instabilities and growth of secondary wake structures. At lower S t c , heave-dominated kinematics demonstrates a strong secondary leading edge vortex (LEV) as the source of growing spanwise instability on the primary LEV, followed by an outflux of streamwise vorticity filaments from the secondary LEV. With increasing heave domination, the origin of stronger spanwise instability is governed by a counter-rotating trailing edge vortex and LEV that leads to growth of streamwise secondary structures. A decreasing heave domination ultimately coincides with an absence of strong LEV undulations and secondary structures. The consistent transition routes are represented on a phase-space map, where a progression of spanwise instability and growth of secondary structures becomes evident within regimes of decreased heave domination. The increasing strength of circulation for the primary LEV, with increasing S t c , provides a crucial reasoning for this newly identified progression.

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“…Data accessibility. The relevant video files, data, open source numerical solver and related documentation are provided in the electronic supplementary material [55].…”

Section: Discussionmentioning

confidence: 99%

Section: (A) Numerical Detailsmentioning

confidence: 99%

Section: Problem Descriptionmentioning

confidence: 99%

Section: Problem Descriptionmentioning

confidence: 99%

See 2 more Smart Citations

On the association of kinematics, spanwise instability and growth of secondary vortex structures in the wake of oscillating foils

Verma,

Khalid,

Hemmati

2023

Proc. R. Soc. A.

Self Cite

View full text Add to dashboard Cite

show abstract

“…The continuity and Navier–Stokes equations were solved directly using OpenFOAM, which is a finite-volume method that has been used extensively for simulating wake dynamics of oscillating foils and panels (Senturk & Smits 2018; Hemmati, Van Buren & Smits 2019; Zheng et al. 2019; Bose, Gupta & Sarkar 2021; Verma & Hemmati 2021 a , b ; Verma, Khalid & Hemmati 2022 b ). The oscillatory foil dynamics was modelled using the overset grid assembly (OGA) method, based on a stationary background grid and a moving overset grid that are merged for the simulation (Petra 2019).…”

Section: Methodsmentioning

confidence: 99%

Characterization of bifurcated dual vortex streets in the wake of an oscillating foil

Verma

Hemmati

2022

J. Fluid Mech.

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Wake evolution of an oscillating foil with combined heaving and pitching motion is evaluated numerically for a range of phase offsets ( $\phi$ ), chord-based Strouhal numbers ( $St_c$ ) and Reynolds numbers ( $Re$ ). The increase in $\phi$ from $90^\circ$ to $180^\circ$ at a given $St_c$ and $Re$ coincides with a transition of pitch- to heave-dominated kinematics that further reveals novel transitions in wake topology characterized by bifurcated vortex streets. At $Re= 1000$ , each of the dual streets constitutes a dipole-like paired configuration of counter-rotating coherent structures that resemble qualitatively the formation of $2P$ mode. A new mathematical relation between the relative circulation of coherent dipole-like paired structures and kinematic parameters is proposed, including heave-based ( $St_h$ ), pitch-based ( $St_{\theta }$ ) and combined motion ( $St_A$ ) Strouhal numbers, as well as $\phi$ . This model can predict accurately the wake transition towards $2P$ mode characterized by a bifurcation, at low $Re= 1000$ . At $Re= 4000$ , however, the relationship was inaccurate in predicting the wake transition. A shear splitting process is observed at $Re= 4000$ , which leads to the formation of reverse Bénard–von Kármán mode in conjunction with $2P$ mode. Increasing $\phi$ further depicts a consistent prolongation of the splitting process, which coincides with a unique transition in terms of absence and reappearance of bifurcated dipole-like pairs at $\phi = 120^\circ$ and $180^\circ$ , respectively. Changes in the spatial arrangement of $2P$ pairs observed consistently for oscillating foils with the combined motion constitute a novel wake transition that becomes more dominant at higher Reynolds numbers.

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Effects of Reynolds number and average angle of attack on the laminar scaling of oscillating foils

2022

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The variation in thrust generation with respect to Reynolds number was numerically evaluated for an oscillating foil with combined pitching and heaving motion at a range of reduced frequencies, amplitudes, and phase offsets. Laminar scaling ([Formula: see text]) was found accurate for a reasonable range of average angle of attack ([Formula: see text]). However, quantitative evaluation of laminar scaling using statistical measures indicates that its capability in predicting thrust variation weakens at higher reduced frequencies and amplitudes. This coincides with an increase in [Formula: see text] above 20°. Evaluation of the pressure and viscous forces revealed a dominance of the former toward total thrust generated at high frequencies for all cases, which also coincided with lower coefficient of determination ( R2) for laminar scaling. The chordwise variation of pressure and skin friction coefficient provided further evidence indicating that pressure, in contrast to the skin friction, did not achieve an asymptotic trend with increasing Reynolds number, especially at higher frequencies and for all phase offsets. Qualitative evaluation of the developing leading edge vortex structure at increasing reduced frequencies and Reynolds numbers also supported the quantitative assessment of chordwise pressure variations. Empirical incorporation of Reynolds number into the complete scaling model was hence completed, which further validates the laminar scaling ([Formula: see text]) of propulsive thrust generation in oscillating foils with a coupled motion.

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On association of lift generation, wake topology and kinematics of oscillating foils

Cited by 4 publications

References 34 publications

On the association of kinematics, spanwise instability and growth of secondary vortex structures in the wake of oscillating foils

On the association of kinematics, spanwise instability and growth of secondary vortex structures in the wake of oscillating foils

Characterization of bifurcated dual vortex streets in the wake of an oscillating foil

Effects of Reynolds number and average angle of attack on the laminar scaling of oscillating foils

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