Scaling laws for the thrust production of flexible pitching panels

2013 ◽  
Vol 732 ◽  
pp. 29-46 ◽  
Author(s):  
Peter A. Dewey ◽  
Birgitt M. Boschitsch ◽  
Keith W. Moored ◽  
Howard A. Stone ◽  
Alexander J. Smits
Keyword(s):  
Scaling Laws ◽  
Leading Edge ◽  
Power Input ◽  
Elastic Force ◽  
Global Maximum ◽  
Propulsive Efficiency ◽  
Fluid Force ◽  
Power Measurements ◽  
Flexible Panels ◽  
Thrust Production

AbstractWe present experimental results on the role of flexibility and aspect ratio in bio-inspired aquatic propulsion. Direct thrust and power measurements are used to determine the propulsive efficiency of flexible panels undergoing a leading-edge pitching motion. We find that flexible panels can give a significant amplification of thrust production of $\mathscr{O}(100{\unicode{x2013}} 200\hspace{0.167em} \% )$ and propulsive efficiency of $\mathscr{O}(100\hspace{0.167em} \% )$ when compared to rigid panels. The data highlight that the global maximum in propulsive efficiency across a range of panel flexibilities is achieved when two conditions are simultaneously satisfied: (i) the oscillation of the panel yields a Strouhal number in the optimal range ($0. 25\lt \mathit{St}\lt 0. 35$) predicted by Triantafyllou, Triantafyllou & Grosenbaugh (J. Fluid Struct., vol. 7, 1993, pp. 205–224); and (ii) this frequency of motion is tuned to the structural resonant frequency of the panel. In addition, new scaling laws for the thrust production and power input to the fluid are derived for the rigid and flexible panels. It is found that the dominant forces are the characteristic elastic force and the characteristic fluid force. In the flexible regime the data scale using the characteristic elastic force and in the rigid limit the data scale using the characteristic fluid force.

scholarly journals Oscillating foils of high propulsive efficiency

1998 ◽  
Vol 360 ◽  
pp. 41-72 ◽  
Author(s):  
J. M. ANDERSON ◽  
K. STREITLIEN ◽  
D. S. BARRETT ◽  
M. S. TRIANTAFYLLOU
Keyword(s):  
Reynolds Number ◽  
High Efficiency ◽  
Leading Edge ◽  
Half Cycle ◽  
Trailing Edge ◽  
Propulsive Efficiency ◽  
Principal Characteristics ◽  
Theoretical Predictions ◽  
Power Measurements ◽  
Oscillating Foils

Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at Reynolds number 1100, and force and power data are measured at Reynolds number 40 000. The experimental results are compared with theoretical predictions of linear and nonlinear inviscid theory and it is found that agreement between theory and experiment is good over a certain parametric range, when the wake consists of an array of alternating vortices and either very weak or no leading-edge vortices form. High propulsive efficiency, as high as 87%, is measured experimentally under conditions of optimal wake formation. Visualization results elucidate the basic mechanisms involved and show that conditions of high efficiency are associated with the formation on alternating sides of the foil of a moderately strong leading-edge vortex per half-cycle, which is convected downstream and interacts with trailing-edge vorticity, resulting eventually in the formation of a reverse Kármán street. The phase angle between transverse oscillation and angular motion is the critical parameter affecting the interaction of leading-edge and trailing-edge vorticity, as well as the efficiency of propulsion.

scholarly journals Effect of Nonuniform Flexibility on Hydrodynamic Performance of Pitching Propulsors

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Samane Zeyghami ◽  
Keith W. Moored
Keyword(s):  
Structural Model ◽  
Fluid Model ◽  
Leading Edge ◽  
Functionally Graded ◽  
Hydrodynamic Performance ◽  
Propulsive Efficiency ◽  
Fluid Structure ◽  
Structure System ◽  
Torsional Spring ◽  
Thrust Production

Many aquatic animals propel themselves efficiently through the water by oscillating flexible fins. These fins are, however, not homogeneously flexible, but instead their flexural stiffness varies along their chord and span. Here, we develop a simple model of these functionally graded materials where the chordwise flexibility of the foil is modeled by one or two torsional springs along the chord line. The torsional spring structural model is then strongly coupled to a boundary element fluid model to simulate the fluid–structure interactions. We show that the effective flexibility of the combined fluid–structure system scales with the ratio of the added mass forces acting on the passive portion of the foil and the elastic forces defined by the torsional spring hinge. Importantly, by considering this new scaling of the effective flexibility, the propulsive performance is then detailed for a foil with a flexible hinge that is actively pitching about its leading edge. The scaling allows for the resonance frequency of the fluid–structure system and the bending pattern of the propulsor to be independently varied by altering the effective flexibility and the location of a single torsional spring along the chord, respectively. It is shown that increasing the flexion ratio, by moving the spring away from the leading edge, leads to enhanced propulsive efficiency, but compromises the thrust production. Proper combination of two flexible hinges, however, can result in a gain in both the thrust production and propulsive efficiency.

Intertwined vorticity and elastodynamics in flapping wing propulsion

2015 ◽  
Vol 787 ◽  
pp. 175-223 ◽  
Author(s):  
Ravi C. Mysa ◽  
Kartik Venkatraman
Keyword(s):  
Strouhal Number ◽  
Leading Edge ◽  
Elastic Solid ◽  
Power Input ◽  
Mirror Image ◽  
Flapping Wing ◽  
Trailing Edge ◽  
Propulsive Efficiency ◽  
Low Frequencies ◽  
Viscous Forces

We performed numerical experiments on a one-dimensional elastic solid oscillating in a two-dimensional viscous incompressible fluid with the intent of discerning the interplay of vorticity and elastodynamics in flapping wing propulsion. Perhaps for the first time, we have established the role of foil deflection topology and its influence on vorticity generation, through spatially and temporally evolving foil slope and curvature. Though the frequency of oscillation of the foil has a definite role, it is the phase relation between foil slope and pressure that determines thrust or drag. Similarly, the phase difference between flapping velocity, and pressure and inertial forces, determine the power input to the foil, and in turn drives propulsive efficiency. At low frequencies of oscillation, the sympathetic slope and curvature of deformation of the foil allow generation of leading-edge vortices that do not separate; they cause substantial rise in pressure between the leading edge and mid-chord. The circulatory component of pressure is determined primarily by the leading-edge vortex and therefore thrust too is predominantly circulatory in origin at low frequencies. In the intermediate and high-frequency range, thrust and drag on the foil spatially alternate and non-circulatory forces dominate over circulatory and viscous forces. For the mass ratios we simulated, thrust due to flapping varies quadratically as a function of Strouhal number or trailing-edge flapping velocity; further, the trailing edge flapping velocities peak at the same set of frequencies where the thrust is also a maximum. Propulsive efficiency, on the other hand, is roughly a mirror image of the thrust variation with respect to Strouhal number. Given that most instances of flapping propulsion in nature are primarily through distributed muscular actuation that enables precise control of deformation shape, leading to high thrust and efficiency, the results presented here are pointers towards understanding some of the mechanisms that drive thrust and propulsive efficiency.

scholarly journals Towards higher aerodynamic efficiency of propeller-driven aircraft with distributed propulsion

2021 ◽  
Author(s):  
Dennis Keller
Keyword(s):  
Performance Indicator ◽  
Leading Edge ◽  
Substantial Improvement ◽  
Initial Assessment ◽  
Local Flow ◽  
Propulsive Efficiency ◽  
Thrust Distribution ◽  
Distributed Propulsion ◽  
Wing Tip ◽  
Cruise Flight

AbstractThe scope of the present paper is to assess the potential of distributed propulsion for a regional aircraft regarding aero-propulsive efficiency. Several sensitivities such as the effect of wingtip propellers, thrust distribution, and shape modifications are investigated based on a configuration with 12 propulsors. Furthermore, an initial assessment of the high-lift performance is undertaken in order to estimate potential wing sizing effects. The performance of the main wing and the propellers are thereby equally considered with the required power being the overall performance indicator. The results indicate that distributed propulsion is not necessarily beneficial regarding the aero-propulsive efficiency in cruise flight. However, the use of wing tip propellers, optimization of the thrust distribution, and wing resizing effects lead to a reduction in required propulsive power by $$-2.9$$ - 2.9 to $$-3.3\,\%$$ - 3.3 % compared to a configuration with two propulsors. Adapting the leading edge to the local flow conditions did not show any substantial improvement in cruise configuration to date.

The Effect of the Configuration of the Amplification Device on the Power Output of a Piezoelectric Strip

2012 ◽  
Author(s):  
Jesse M. McCarthy ◽  
Arvind Deivasigamani ◽  
Sabu J. John ◽  
Simon Watkins ◽  
Floreana Coman
Keyword(s):  
Aspect Ratio ◽  
Power Output ◽  
Polyvinylidene Fluoride ◽  
Leading Edge ◽  
Wind Speeds ◽  
Start Up ◽  
Piezoelectric Strip ◽  
Power Measurements ◽  
System 1 ◽  
Leaf Parameters

We investigated the behaviour of a polyvinylidene-fluoride piezoelectric strip (‘stalk’) clamped at the leading edge, and hinged to an amplification device (‘leaf’) at the trailing edge. Flutter of this cantilevered system was induced within smooth, parallel flow, and an AC voltage was generated from the PVDF strip. A polypropylene, triangle comprised the leaf. Two leaf parameters were varied so as to quantify their effect on the power output of the system: 1) the area, and 2) the aspect ratio. It was found that the highest power output was realised with the 2nd-largest leaf across a range of wind speeds, but the variation in power measurements was large. Thus, the 3rd-largest leaf was found to give the highest power output with the lowest power variation. This leaf area was then fixed and the aspect ratio varied. It was found that the largest aspect ratio-leaf rendered the highest power output, but had a relatively high start-up wind speed.

Effect of pectoral fin kinematics on manta ray propulsion

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840025
Author(s):  
Hao Lu ◽  
Khoon Seng Yeo ◽  
Chee-Meng Chew
Keyword(s):  
Leading Edge ◽  
Wave Model ◽  
Pectoral Fin ◽  
Long Distance ◽  
Propulsive Efficiency ◽  
Fish Locomotion ◽  
Pectoral Fins ◽  
Flow Features ◽  
Edge Vortex ◽  
Manta Ray

Recent advancement of bio-inspired underwater vehicles has led to a growing interest in understanding the fluid mechanics of fish locomotion, which involves complex interaction between the deforming structure and its surrounding fluid. Unlike most natural swimmers that undulate their body and caudal fin, manta rays employ an oscillatory mode by flapping their large, flattened pectoral fins to swim forward. Such a lift-based mode can achieve a substantially high propulsive efficiency, which is beneficial to long-distance swimming. In this study, numerical simulations are carried out on a realistic manta ray model to investigate the effect of pectoral fin kinematics on the propulsive performance and flow structure. A traveling wave model, which relates a local deflection angle to radial and azimuthal wavelengths, is applied to generate the motion of the pectoral fins. Hydrodynamic forces and propulsive efficiency are reported for systematically varying kinematic parameters such as wave amplitude and wavelengths. Key flow features, including a leading edge vortex (LEV) that forms close to the tip of each pectoral fin, and a wake consisting of interconnected vortex rings, are identified. In addition, how different fin motions alter the LEV behavior and hence affect the thrust and efficiency is illustrated.

scholarly journals Three-dimensional scaling laws of cetacean propulsion characterize the hydrodynamic interplay of flukes' shape and kinematics

2020 ◽  
Vol 17 (163) ◽  
pp. 20190655 ◽  
Author(s):  
Fatma Ayancik ◽  
Frank E. Fish ◽  
Keith W. Moored
Keyword(s):  
Aspect Ratio ◽  
Scaling Laws ◽  
Three Dimensional ◽  
Force Production ◽  
Numerical Data ◽  
Added Mass ◽  
Cetacean Species ◽  
Propulsive Efficiency ◽  
Fluid Environment ◽  
Pitch Ratio

Cetaceans convert dorsoventral body oscillations into forward velocity with a complex interplay between their morphological and kinematic features and the fluid environment. However, it is unknown to what extent morpho-kinematic features of cetaceans are intertwined to maximize their efficiency. By interchanging the shape and kinematic variables of five cetacean species, the interplay of their flukes morpho-kinematic features is examined by characterizing their thrust, power and propulsive efficiency. It is determined that the shape and kinematics of the flukes have considerable influence on force production and power consumption. Three-dimensional heaving and pitching scaling laws are developed by considering both added mass and circulatory-based forces, which are shown to closely model the numerical data. Using the scaling relations as a guide, it is determined that the added mass forces are important in predicting the trend between the efficiency and aspect ratio, however, the thrust and power are driven predominately by the circulatory forces. The scaling laws also reveal that there is an optimal dimensionless heave-to-pitch ratio h * that maximizes the efficiency. Moreover, the optimal h * varies with the aspect ratio, the amplitude-to-chord ratio and the Lighthill number. This indicates that the shape and kinematics of propulsors are intertwined, that is, there are specific kinematics that are tailored to the shape of a propulsor in order to maximize its propulsive efficiency.

Leading edge strengthening and the propulsion performance of flexible ray fins

2012 ◽  
Vol 693 ◽  
pp. 402-432 ◽  
Author(s):  
Kourosh Shoele ◽  
Qiang Zhu
Keyword(s):  
Phase Difference ◽  
Structural Characteristics ◽  
Leading Edge ◽  
Immersed Boundary ◽  
Propulsion Performance ◽  
Thrust Generation ◽  
Generation Capacity ◽  
Effective Angle ◽  
Edge Separation ◽  
Thrust Production

AbstractA numerical model of a ray-reinforced fin is developed to investigate the relation between its structural characteristics and its force generation capacity during flapping motion. In this two-dimensional rendition, the underlying rays are modelled as springs, and the membrane is modelled as a flexible but inextensible plate. The fin kinematics is characterized by its oscillation frequency and the phase difference between different rays (which generates a pitching motion). An immersed boundary method (IBM) is applied to solve the fluid–structure interaction problem. The focus of the current paper is on the effects of ray flexibility, especially the detailed distribution of ray stiffness, upon the capacity of thrust generation. The correlation between thrust generation and features of the surrounding flow (especially the leading edge separation) is also examined. Comparisons are made between a fin with rigid rays, a fin with identical flexible rays, and a fin with flexible rays and strengthened leading edge. It is shown that with flexible rays, the thrust production can be significantly increased, especially in cases when the phase difference between different rays is not optimized. By strengthening the leading edge, a higher propulsion efficiency is observed. This is mostly attributed to the reduction of the effective angle of attack at the leading edge, accompanied by mitigation of leading edge separation and dramatic changes in characteristics of the wake. In addition, the flexibility of the rays causes reorientation of the fluid force so that it tilts more towards the swimming direction and the thrust is thus increased.

Undulatory median fin propulsion of two teleosts with different modes of life

1980 ◽  
Vol 58 (11) ◽  
pp. 2116-2119 ◽  
Author(s):  
R. W. Blake
Keyword(s):  
Electric Fish ◽  
Flow Model ◽  
Low Frequency ◽  
Leading Edge ◽  
Large Area ◽  
Propulsive Efficiency ◽  
Dorsal Fin ◽  
Gymnarchus Niloticus ◽  
Mode Of Life ◽  
Modes Of Life

A simple fluid flow model, based on momentum considerations, is employed to calculate the hydromechnanical efficiency of the undulatory dorsal fin propeller of the electric fish (Gymnarchus niloticus) and the seahorse (Hippocampus hudsonius). The undulatory fins of G. niloticus and H. hudsonius are representative of two extreme kinematic styles. The dorsal fin of G. niloticus is characterized by waveforms which are propagated at low frequency and a leading edge which "sweeps out" a large area. In contrast, the leading edge of the dorsal fin of H. hudsonius sweeps out a comparatively small area and waveforms pass down the fin at a high frequency. It is shown that the propulsive efficiency of the dorsal fin of G. niloticus can be up to twice that of H. hudsonius at similar swimming speeds. Possible explanations for the evolution of the two kinematic modes are discussed in relation to the mode of life of the animals.

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