Numerical Study on Thrust Generation Performance of Plunging Airfoils

2013 ◽  
Vol 312 ◽  
pp. 235-238
Author(s):  
Ji Gao ◽  
Rui Shan Yuan ◽  
Ming Hui Zhang ◽  
Yong Hui Xie
Keyword(s):  
Viscous Flow ◽  
Numerical Study ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Propulsion Performance ◽  
Incompressible Viscous Flow ◽  
Thrust Generation ◽  
The Difference

In this paper, the effects of angle of attack, camber and camber location on propulsion performance of flapping airfoils undergoing plunging motion were numerically studied at Re=20000 and h=0.175. The unsteady incompressible viscous flow around four different airfoil sections was simulated applying the dynamic mesh. The results show that the time averaged thrust coefficient CTmean and propulsive efficiency η of the symmetric airfoil decrease with the increasing angle of attack, and the variation of CTmean is more obvious than that of CPmean. Both CTmean and η for NACA airfoils studied in this paper decrease with the increasing camber and the difference between the propulsion performances of different airfoils is not obvious, and the thrust generation and power of various NACA airfoils gradually increase during the downstroke and decrease during the upstroke. Under the same conditions, the airfoil with a further distance between the maximum camber location and the chord of the leading edge leads to higher propulsive efficiency.

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.

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.

scholarly journals Influence of Thickness Variation on the Flapping Performance of Symmetric NACA Airfoils in Plunging Motion

2010 ◽  
Vol 2010 ◽  
pp. 1-19 ◽  
Author(s):  
Liangyu Zhao ◽  
Shuxing Yang
Keyword(s):  
Lift Coefficient ◽  
Parametric Method ◽  
Leading Edge ◽  
Thickness Variation ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Maximum Thickness ◽  
Class Function ◽  
Edge Vortex ◽  
The Impact

In order to investigate the impact of airfoil thickness on flapping performance, the unsteady flow fields of a family of airfoils from an NACA0002 airfoil to an NACA0020 airfoil in a pure plunging motion and a series of altered NACA0012 airfoils in a pure plunging motion were simulated using computational fluid dynamics techniques. The “class function/shape function transformation“ parametric method was employed to decide the coordinates of these altered NACA0012 airfoils. Under specified plunging kinematics, it is observed that the increase of an airfoil thickness can reduce the leading edge vortex (LEV) in strength and delay the LEV shedding. The increase of the maximum thickness can enhance the time-averaged thrust coefficient and the propulsive efficiency without lift reduction. As the maximum thickness location moves towards the leading edge, the airfoil obtains a larger time-averaged thrust coefficient and a higher propulsive efficiency without changing the lift coefficient.

Note on optimum propulsion of heaving and pitching airfoils from linear potential theory

2017 ◽  
Vol 826 ◽  
pp. 781-796 ◽  
Author(s):  
R. Fernandez-Feria
Keyword(s):  
Phase Shift ◽  
Potential Theory ◽  
Linear Theory ◽  
Leading Edge ◽  
Linear Potential ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Pitching Motion ◽  
Reduced Frequency ◽  
Linear Potential Theory

The conditions that maximize the propulsive efficiency of a heaving and pitching airfoil are analysed using a novel formulation for the thrust force within the linear potential theory. Stemming from the vortical impulse theory, which correctly predicts the decay of the thrust efficiency as the inverse of reduced frequency$k$for large$k$(Fernandez-Feria,Phys. Rev. Fluids, vol. 1, 2016, 084502), the formulation is corrected here at low frequencies by adding a constant representing the viscous drag. It is shown first that the thrust coefficient and propulsive efficiency thus computed agree quite well with several sets of available experimental data, even for not so small flapping amplitudes. For a pure pitching motion, it is found that the maximum propulsion efficiency is reached for the airfoil pitching close to the three-quarter chord point from the leading edge with a relatively large reduced frequency, corresponding to a relatively low thrust coefficient. According to the theory, this efficiency peak may approach unity. For smaller$k$, other less pronounced local maxima of the propulsive efficiency are attained for pitching points ahead of the leading edge, with larger thrust coefficients. The linear theory also predicts that no thrust is generated at all for a pitching axis located between the three-quarter chord point and the trailing edge. These findings contrast with the results obtained from the classical linear thrust by Garrick, with the addition of the same quasi-static thrust, which are also computed in the paper. For a combined heaving and pitching motion, the behaviour of the propulsive efficiency in relation to the pitching axis is qualitatively similar to that found for a pure pitching motion, for given fixed values of the feathering parameter (ratio between pitching and heaving amplitudes) and of the phase shift between the pitching and heaving motions. The peak propulsive efficiency predicted by the linear theory is for an airfoil with a pitching axis close to, but ahead of, the three-quarter chord point, with a relatively large reduced frequency, a feathering parameter of approximately$0.9$and a phase shift slightly smaller than $90^{\circ }$.

Hydromechanics of lunate-tail swimming propulsion

1974 ◽  
Vol 64 (2) ◽  
pp. 375-392 ◽  
Author(s):  
M. G. Chopra
Keyword(s):  
Aspect Ratio ◽  
Leading Edge ◽  
Vortex Sheet ◽  
The Body ◽  
Uniform Motion ◽  
Physical Parameters ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Reduced Frequency ◽  
General Motion

This paper investigates the non-uniform motion of a thin plate of finite aspect ratio, with a rounded leading edge and sharp trailing edge, executing heaving and pitching oscillations at zero mean lift. Such vertical motions characterize the horizontal lunate tails with which cetacean mammals propel themselves, and the same motions, turned through 90° to become horizontal motions of sideslip and yaw, characterize the vertical lunate tails of certain fast-swimming fishes. An oscillating vortex sheet consisting of streamwise and spanwise components is shed to trail behind the body and it is this additional feature of the streamwise component resulting from the finiteness of the plate that makes this study a generalization of the two-dimensional treatment of lunate-tail propulsion by Lighthill (1970). The forward thrust, the power required, the energy imparted to the wake and the hydromechanical propulsive efficiency are determined for this general motion as functions of the physical parameters defining the problem: namely the aspect ratio, the reduced frequency, the feathering parameter and the position of the pitching axis. The dependence of the thrust coefficient and propulsive efficiency on these physical parameters, for the complete range of variation consistent with the assumptions of the problem, has been depicted graphically.

scholarly journals Optimization of Flapping Airfoils for Maximum Thrust and Propulsive Efficiency

10.14311/508 ◽  
2004 ◽  
Vol 44 (1) ◽  
Author(s):  
I. H. Tuncer ◽  
M. Kay
Keyword(s):  
Large Scale ◽  
High Efficiency ◽  
Leading Edge ◽  
Laminar Flows ◽  
Navier Stokes ◽  
Propulsive Efficiency ◽  
Thrust Generation ◽  
Optimization Function ◽  
Optimization Parameters ◽  
Large Scale Vortex

A numerical optimization algorithm based on the steepest decent along the variation of the optimization function is implemented for maximizing the thrust and/or propulsive efficiency of a single flapping airfoil. Unsteady, low speed laminar flows are computed using a Navier-Stokes solver on moving overset grids. The flapping motion of the airfoil is described by a combined sinusoidal plunge and pitching motion. Optimization parameters are taken to be the amplitudes of the plunge and pitching motions, and the phase shift between them. Computations are performed in parallel in a work station cluster. The numerical simulations show that high thrust values may be obtained at the expense of reduced efficiency. For high efficiency in thrust generation, the induced angle of attack of the airfoil is reduced and large scale vortex formations at the leading edge are prevented. 

Study of Aerodynamic Interactions of Dual Flapping Airfoils in Tandem Configurations

2012 ◽  
Vol 160 ◽  
pp. 301-306
Author(s):  
Bao Li Zhu ◽  
Hui Pen Wu ◽  
Tian Hang Xiao
Keyword(s):  
Viscous Flow ◽  
Great Influence ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Propulsive Efficiency ◽  
Motion Models ◽  
Hybrid Meshes ◽  
Thrust Generation ◽  
Unsteady Viscous Flow ◽  
Flapping Airfoil

The unsteady viscous flow fields of dual flapping airfoils in tandem configurations are simulated by a Navier-Stokes Solver based on dynamic deformable hybrid meshes. Aerodynamic interactions of three motion models are studied including flapping fore airfoil with fixed aft airfoil, two airfoils flapping in phase and out-of-phase. The results indicate that the aft airfoil in the wake of the flapping fore airfoil has great influence on the aerodynamic performance. When the fore airfoil flaps with a fixed aft airfoil, the thrust generation and thrust propulsive efficiency were enhanced by 65% and 44% respectively, compared to that of single flapping airfoil. When the two airfoils stoke in phase, the thrust generation is twice over that of single flapping airfoil. However the out-of-phase stroking has relatively much lower thrust.

Large amplitude lunate-tail theory of fish locomotion

1976 ◽  
Vol 74 (1) ◽  
pp. 161-182 ◽  
Author(s):  
M. G. Chopra
Keyword(s):  
Angle Of Attack ◽  
Leading Edge ◽  
Finite Amplitude ◽  
Dimensional Theory ◽  
Propulsive Efficiency ◽  
Suction Force ◽  
Fish Locomotion ◽  
Reduced Frequency ◽  
Accurate Comparison ◽  
Arbitrary Amplitude

The two-dimensional theory of lunate-tail propulsion is extended to motions of arbitrary amplitude, regular or irregular, so that an accurate comparison may be made with the actual lunate-tail propulsion of scombroid fishes and cetacean mammals. There is no restriction at all on the amplitude of motion but the tail's angle of attack relative to its instantaneous path through the water is assumed to remain small. The theory is applied to the regular finite amplitude motion of a thin aerofoil with a rounded leading edge to take advantage of the suction force and a sharp trailing edge to ensure smooth tangential flow past the rear tip. This can represent the vertical motions of the horizontal lunate tails of large aspect ratio with which cetacean mammals propel themselves or the horizontal undulations of the vertical lunate tails of certain fast fishes. The dependence of the thrust, the hydromechanical propulsive efficiency and the energy wasted in churning up the eddying wake on the reduced frequency, the angle of attack and the amplitude of motion is exhibited.

scholarly journals Numerical Analysis of the Effect of Flexibility on the Propulsive Performance of a Heaving Hydrofoil Undergoing Sinusoidal and Non-Sinusoidal Motions

2021 ◽  
Vol 28 (4) ◽  
pp. 4-19
Author(s):  
Fengkun Li ◽  
Pengyao Yu ◽  
Qiang Wang ◽  
Guangzhao Li ◽  
Xiangcheng Wu
Keyword(s):  
Large Scale ◽  
Time Varying ◽  
Constant Amplitude ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Structure Interaction ◽  
Propulsive Performance ◽  
Passive Deformation ◽  
Thrust Generation ◽  
Maximum Thrust

Abstract Numerical simulations of fluid-structure interaction (FSI) on an elastic foil heaving with constant amplitude in freestream flow are carried out at a low Reynolds number of 20,000. The commercial software STAR-CCM+ is employed to solve the flow field and the large-scale passive deformation of the structure. The results show that introducing a certain degree of flexibility significantly improves the thrust and efficiency of the foil. For each Strouhal number St considered, an optimal flexibility exists for thrust; however, the propulsive efficiency keeps increasing with the increase in flexibility. The visualisation of the vorticity fields elucidates the improvement of the propulsive characteristics by flexibility. Furthermore, the mechanism of thrust generation is discussed by comparing the time-varying thrust coefficient and vortex structure in the wake for both rigid and elastic foils. Finally, in addition to sinusoidal motions, we also consider the effect of non-sinusoidal trajectories defined by flattening parameter S on the propulsive characteristics for both rigid and elastic foils. The non-sinusoidal trajectories defined by S=2 are associated with the maximum thrust, and the highest values of propulsive efficiency are obtained with S=0.5 among the cases considered in this work.

Numerical Study on Flap Style Rudder Hydrodynamic Characteristics With Different Connections

2016 ◽  
Author(s):  
Zhenwei Dong ◽  
Zhijian Xiao ◽  
Shiqi Gong ◽  
Zhiguo Zhang ◽  
Dakui Feng
Keyword(s):  
Numerical Study ◽  
Angle Of Attack ◽  
Large Angle ◽  
Hydrodynamic Characteristics ◽  
Computation Method ◽  
Suction Surface ◽  
Drag Coefficients ◽  
Flow Field Characteristics ◽  
The Difference ◽  
Lift And Drag

The flow field characteristics of 2-D flap style rudders with and without gap are analyzed through 4 models. To explore the influence of different filling styles, one flap rudder with gap and three flap rudders without gap are simulated from 0 to 30 degrees angle of attack with k-omega SST turbulence model. Validation is done by comparing the results with EFD data from reference and the mesh independence verification is also made. Then lift and drag coefficients are compared among four models. Pressure, velocity distributions are given to explain the difference on hydrodynamic characteristics among them. Unsteady computation method is used to investigate the fluctuation characteristics of drag coefficients at large angle of attack. Stream lines are shown to better understand the vortex system on the suction surface.

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