Thrust generation by a heaving flexible foil: Resonance, nonlinearities, and optimality

2016 ◽  
Vol 28 (1) ◽  
pp. 011903 ◽  
Author(s):  
Florine Paraz ◽  
Lionel Schouveiler ◽  
Christophe Eloy
Keyword(s):  
Thrust Generation

Thrust generation from pitching foils with flexible trailing edge flaps

2017 ◽  
Vol 828 ◽  
pp. 70-103 ◽  
Author(s):  
M. Jimreeves David ◽  
R. N. Govardhan ◽  
J. H. Arakeri
Keyword(s):  
Flexural Rigidity ◽  
Resonance Condition ◽  
Stream Velocity ◽  
Peak Efficiency ◽  
Trailing Edge ◽  
Axial Thrust ◽  
Thrust Coefficient ◽  
Rigidity Parameter ◽  
Thrust Generation ◽  
Flap Deflection

In the present experimental study, we investigate thrust production from a pitching flexible foil in a uniform flow. The flexible foils studied comprise a rigid foil in the front (chord length $c_{R}$) that is pitched sinusoidally at a frequency $f$, with a flexible flap of length $c_{F}$ and flexural rigidity $EI$ attached to its trailing edge. We investigate thrust generation for a range of flexural rigidities ($EI$) and flap length to total chord ratio ($c_{F}/c$), with the mean thrust ($\overline{C_{T}}$) and the efficiency of thrust generation ($\unicode[STIX]{x1D702}$) being directly measured in each case. The thrust in the rigid foil cases, as expected, is found to be primarily due to the normal force on the rigid foil ($\overline{C_{TN}}$) with the chordwise or axial thrust contribution ($\overline{C_{TA}}$) being small and negative. In contrast, in the flexible foil cases, the axial contribution to thrust becomes important. We find that using a non-dimensional flexural rigidity parameter ($R^{\ast }$) defined as $R^{\ast }=EI/(0.5\unicode[STIX]{x1D70C}U^{2}c_{F}^{3})$ appears to combine the independent effects of variations in $EI$ and $c_{F}/c$ at a given value of the reduced frequency ($k=\unicode[STIX]{x03C0}fc/U$) for the range of $c_{F}/c$ values studied here ($U$ is free-stream velocity; $\unicode[STIX]{x1D70C}$ is fluid density). At $k\approx 6$, the peak mean thrust coefficient is found to be about 100 % higher than the rigid foil thrust, and occurs at $R^{\ast }$ value of approximately 8, while the peak efficiency is found to be approximately 300 % higher than the rigid foil efficiency and occurs at a distinctly different $R^{\ast }$ value of close to 0.01. Corresponding to these two optimal flexural rigidity parameter values, we find two distinct flap deflection shapes; the peak thrust corresponding to a mode 1 type simple bending of the flap with no inflection points, while the peak efficiency corresponds to a distinctly different deflection profile having an inflection point along the flap. The peak thrust condition is found to be close to the ‘resonance’ condition for the first mode natural frequency of the flexible flap in still water. In both these optimal cases, we find that it is the axial contribution to thrust that dominates ($\overline{C_{TA}}\gg \overline{C_{TN}}$), in contrast to the rigid foil case. Particle image velocimetry (PIV) measurements for the flexible cases show significant differences in the strength and arrangement of the wake vortices in these two cases.

scholarly journals Swimming like algae: biomimetic soft artificial cilia

2013 ◽  
Vol 10 (78) ◽  
pp. 20120666 ◽  
Author(s):  
Sina Sareh ◽  
Jonathan Rossiter ◽  
Andrew Conn ◽  
Knut Drescher ◽  
Raymond E. Goldstein
Keyword(s):  
Smart Materials ◽  
Fluid Transport ◽  
Metal Composite ◽  
Ionic Polymer ◽  
Piecewise Constant ◽  
Ciliary Motion ◽  
Thrust Generation ◽  
Artificial Cilia ◽  
Segmentation Pattern ◽  
Polymer Metal

Cilia are used effectively in a wide variety of biological systems from fluid transport to thrust generation. Here, we present the design and implementation of artificial cilia, based on a biomimetic planar actuator using soft-smart materials. This actuator is modelled on the cilia movement of the alga Volvox , and represents the cilium as a piecewise constant-curvature robotic actuator that enables the subsequent direct translation of natural articulation into a multi-segment ionic polymer metal composite actuator. It is demonstrated how the combination of optimal segmentation pattern and biologically derived per-segment driving signals reproduce natural ciliary motion. The amenability of the artificial cilia to scaling is also demonstrated through the comparison of the Reynolds number achieved with that of natural cilia.

scholarly journals Computational Analysis of Propulsion Performance of Modified Pitching Motion Airfoils in Laminar Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-13
Author(s):  
Yonghui Xie ◽  
Kun Lu ◽  
Di Zhang ◽  
Gongnan Xie
Keyword(s):  
Laminar Flow ◽  
Cfd Modeling ◽  
Shape Effect ◽  
Optimal Range ◽  
Propulsive Efficiency ◽  
Pitching Motion ◽  
Propulsion Performance ◽  
Reduced Frequency ◽  
Thrust Generation ◽  
The Cost

The thrust generation performance of airfoils with modified pitching motion was investigated by computational fluid dynamics (CFD) modeling two-dimensional laminar flow at Reynolds number of 104. The effect of shift distance of the pitch axis outside the chord line(R), reduced frequency(k), pitching amplitude(θ), pitching profile, and airfoil shape (airfoil thickness and camber) on the thrust generated and efficiency were studied. The results reveal that the increase inRandkleads to an enhancement in thrust generation and a decrease in propulsive efficiency. Besides, there exists an optimal range ofθfor the maximum thrust and the increasingθinduces a rapid decrease in propulsive efficiency. Six adjustable parameters(K)were employed to realize various nonsinusoidal pitching profiles. An increase inKresults in more thrust generated at the cost of decreased propulsive efficiency. The investigation of the airfoil shape effect reveals that there exists an optimal range of airfoil thickness for the best propulsion performance and that the vortex structure is strongly influenced by the airfoil thickness, while varying the camber or camber location of airfoil sections offers no benefit in thrust generation over symmetric airfoil sections.

Thrust Generation with Low-Power Continuous-Wave Laser and Aluminum Foil Interaction

2010 ◽  
Author(s):  
Hideyuki Horisawa ◽  
Sota Sumida ◽  
Ikkoh Funaki ◽  
Claude Phipps ◽  
Kimiya Komurasaki ◽  
...  
Keyword(s):  
Low Power ◽  
Continuous Wave ◽  
Aluminum Foil ◽  
Continuous Wave Laser ◽  
Thrust Generation ◽  
Wave Laser

A Study on Kinematic Pattern of Fish Undulatory Locomotion Using a Robot Fish

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Yong Zhong ◽  
Jialei Song ◽  
Haoyong Yu ◽  
Ruxu Du
Keyword(s):  
The Body ◽  
Control Methods ◽  
Kinematic Pattern ◽  
Thrust Generation ◽  
Yaw Stability ◽  
Sinusoidal Pattern ◽  
Undulatory Locomotion ◽  
Robot Fish ◽  
Kinematic Optimization ◽  
Surrounding Fluid

Recent state-of-art researches on robot fish focus on revealing different swimming mechanisms and developing control methods to imitate the kinematics of the real fish formulated by the so-called Lighthill's theory. However, the reason why robot fish must follow this formula has not been fully studied. In this paper, we adopt a biomimetic untethered robot fish to study the kinematics of fish flapping. The robot fish consists of a wire-driven body and a soft compliant tail, which can perform undulatory motion using one motor. A dynamic model integrated with surrounding fluid is developed to predict the cruising speed, static thrust, dynamic thrust, and yaw stability of the robot fish. Three driving patterns of the motor are experimented to achieve three kinematic patterns of the robot fish, e.g., triangular pattern, sinusoidal pattern, and an over-cambered sinusoidal pattern. Based on the experiment results, it is found that the sinusoidal pattern generated the largest average static thrust and steady cruising speed, while the triangular pattern achieved the best yaw stability. The over-cambered sinusoidal pattern was compromised in both metrics. Moreover, the kinematics study has shown that the body curves of the robot fish were similar to the referenced body curves presented by the formula when using the sinusoidal pattern, especially the major thrust generation area. This research provides a guidance on the kinematic optimization and motor control of the undulatory robot fish.

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.

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