Dynamics of flow around a pitching hydrofoil

Alam, Md. Mahbub; Muhammad, Zaka

doi:10.1016/j.jfluidstructs.2020.103151

Cited by 32 publications

(42 citation statements)

References 31 publications

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“…The thrust efficiency of the hydrofoil is then estimated as: grids 2 and 3, hence grid 2 was chosen for further simulations. The details of thorough validation performed can be found in Alam & Muhammad [14]. FollowingC T , the η is also negative and positive with the same boundary.…”

Section: Numerical Modelmentioning

confidence: 86%

Pitching Hydrofoil: Inviscid Analysis and Scaling Parameters

Alam¹,

Muhammad²

2020

Australasian Fluid Mechanics Conference (AFMC)

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A parametric study on a forced pitching hydrofoil is performed on Strouhal number St d -A * (pitching-amplitude ratio) plane. The numerical solution is obtained using unsteady Navier-Stokes equations. The average thrust, power and efficiency of the pitching hydrofoil is discussed for conditions corresponding to both drag and thrust. A flow model is hypothesized with mathematical analysis of the flow involving Euler, Coriolis and centrifugal accelerations in a non-inertial frame of reference. The flow model provides the physical insight into the thrust generation and power input, and also provides theoretical relationships of thrust, power, and efficiency as functions of Strouhal number and/or amplitude ratio. The data from the numerical simulation tangibly support the relationships.

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Section: Numerical Modelmentioning

confidence: 86%

Pitching Hydrofoil: Inviscid Analysis and Scaling Parameters

Alam¹,

Muhammad²

2020

Australasian Fluid Mechanics Conference (AFMC)

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“…The foil is tear-shaped, with a semi-circular blunt leading edge and a tapered foil tip, extensively used in the literature (Godoy-Diana et al 2008Schnipper et al 2009;Marais et al 2012;Andersen et al 2016;Alam & Muhammad 2020;and others). The chord (c) to thickness (d) ratio of the foil is c/d = 5.1, and the foil pitches about the centre (marked with a '+' sign) of the semi-circular leading edge (figure 2a).…”

Section: Model and Parametersmentioning

confidence: 99%

“…The dimensionless form of the amplitude is A * and that of the frequency is the Strouhal number St d , which lie in the ranges of 1.1-1.6 and 0.21-0.33, respectively. The A * is selected based on the natural range of the tail amplitude of various fish, as reported by Floryan et al (2017), while St d is based on the natural swimmers (Godoy-Diana et al 2008;Alam & Muhammad 2020). The corresponding St A (= St d × A * ) nestles within the range observed in swimming animals, fish and cetacean (Triantafyllou, Triantafyllou & Gopalkrishnan 1991;Taylor, Nudds & Thomas 2003;Eloy 2012).…”

Section: Model and Parametersmentioning

confidence: 99%

“…Additionally, differences in the aerodynamic forces between the 2-D and the 3-D simulations were less than 5 %. Alam & Muhammad (2020) also compared results between 2-D and 3-D simulations at Re d = 200 and found that the flow around the oscillating foil at Re d = 200 is essentially 2-D. The maximum instantaneous thrust is generated at the instant where the rate of power input changes from positive to negative, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…The St d , A * , pitching centre and attack angle are all pivotal parameters for thrust generation and efficiency (Triantafyllou et al 2005;Alam & Muhammad 2020). For a given angular amplitude of the foil oscillation, when the pitching centre moves from the leading edge to the foil tip (trailing edge), the amplitude of the foil tail shrinks and hence thrust drops (Tian et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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Efficient thrust enhancement by modified pitching motion

2021

Self Cite

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Thrust and/or efficiency of a pitching foil (mimicking a tail of swimming fish) can be enhanced by tweaking the pitching waveform. The literature, however, show that non-sinusoidal pitching waveforms can enhance either thrust or efficiency but not both simultaneously. With the knowledge and inspiration from nature, we devised and implemented a novel asymmetrical sinusoidal pitching motion that is a combination of two sinusoidal motions having periods T1 and T2 for the forward and retract strokes, respectively. The motion is represented by period ratio $\mathrm{\mathbb{T}} = {T_1}/T$ , where T = (T1 + T2)/2, with $\mathrm{\mathbb{T}} > 1.00$ giving the forward strokes (from equilibrium to extreme position) slower than the retract strokes (from extreme to equilibrium position) and vice versa. The novel pitching motion enhances both thrust and efficiency for $\mathrm{\mathbb{T}} > 1.00$ . The enhancement results from the resonance between the shear-layer roll up and the increased speed of the foil. Four swimming regimes, namely normal swimming, undesirable, floating and ideal are discussed, based on instantaneous thrust and power. The results from the novel pitching motion display similarities with those from fish locomotion (e.g. fast start, steady swimming and braking). The $\mathrm{\mathbb{T}} > 1.00$ motion in the faster stroke has the same characteristics and results as the fast start of prey to escape from a predator while $\mathrm{\mathbb{T}} < 1.00$ imitates braking locomotion. While $\mathrm{\mathbb{T}} < 1.00$ enhances the wake deflection at high amplitude-based Strouhal numbers (StA = fA/U∞, where f and A are the frequency and peak-to-peak amplitude of the pitching, respectively, and U∞ is the freestream velocity), $\mathrm{\mathbb{T}} > 1.00$ improves the wake symmetry, suppressing the wake deflection. The wake characteristics including wake width, jet velocity and vortex structures are presented and connected with $S{t_d}( = fd/{U_\infty })$ , ${A^{\ast}}( = A/d)$ and $\mathrm{\mathbb{T}}$ , where d is the maximum thickness of the foil.

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