Chord Line Research Articles

Effect of curvature variations on the hydrodynamic performance of heaving and pitching foils

AbstractThe use of heaving and pitching fins for underwater propulsion of engineering devices poses an attractive outlook given the efficiency and adaptability of natural fish. However, significant knowledge gaps need to be bridged before biologically inspired propulsion is able to operate at competitive performances in a practical setting. One of these relates to the design of structures that can leverage passive deformation and active morphing in order to achieve optimal hydrodynamic performance. To provide insights into the performance improvements associated with passive and active fin deformations, we provide here a systematic numerical investigation in the thrust, power, and efficiency of 2D heaving and pitching fins with imposed curvature variations. The results show that for a given chordline kinematics, the use of curvature can improve thrust by 70% or efficiency by 35% over a rigid fin. Maximum thrust is achieved when the camber variations are synchronized with the maximum heave velocity, increasing the overall magnitude of the force vector while increasing efficiency as well. Maximum efficiency is achieved when camber is applied during the first half of the stroke, tilting the force vector to create thrust earlier in the cycle than a comparable rigid fin. Overall, our results demonstrate that curving fins are consistently able to significantly outperform rigid fins with the same chord line kinematics on both thrust and hydrodynamic efficiency.

A general framework for the design of efficient passive pitch systems

Mitigating the impact of variable inflow conditions is critical for a wide range of engineering systems such as drones or wind and tidal turbines. Passive control systems are of increasing interest for their inherent reliability, but a mathematical framework to aid the design of such systems is currently lacking. To this end, in this paper a two-dimensional rigid foil that passively pitches in response to changes in the flow velocity is considered. Both an analytical quasi-steady model and a dynamic low-order model are developed to investigate the pivot point position that maximizes unsteady load mitigation. The paper focuses on streamwise gusts, but the proposed methodology would apply equally to any change in the inflow velocity (speed and/or direction). The quasi-steady model shows that the force component in any arbitrary direction can be kept constant if the pivot lies on a particular line, and that the line coordinates depend on the gust and the foil characteristics. The dynamic model reveals that the optimum distance of the pivot location from the foil increases with decreasing inertia. For a foil at small angles of incidence, the optimum pivot point is along the extended chord line. This knowledge provides a methodology to design optimum passively pitching systems for a plethora of applications, including flying and swimming robotic vehicles, and provides new insights into the underlying physics of gust mitigation.

Conformally Decambered Natural Laminar Flow Blades for Vertical-Axis Wind Turbines

A two-element natural laminar flow airfoil—commonly used on medium-altitude, long-endurance, unmanned air vehicles—was conformally decambered for application on a two-bladed, H-rotor, vertical-axis wind turbine. Blade kinematics were used to determine the virtual camber line, which was then used to conformally map the original profile onto the chord line. Both decambered and original blade profiles were evaluated experimentally using large chord-radius ratios (0.6 and 0.75) that exploited dynamic stall to produce the driving torque. Decambered blades showed substantially greater power and torque coefficients than the original blades, up to 60 and 27%, respectively, which represents the first experimental validation of conformal decambering. Relatively large peak power coefficients of 0.28 were attained, despite maximum chord-based Reynolds numbers being less than 2×105. Depending upon the chord-radius ratio, either light or deep dynamic stall occurred in the second upstream quadrant, and the flap flow remained attached virtually throughout. In contrast, on the original profiles, massive separation was observed on the blades, and the flap flow remained separated due to assumed outer surface flow separation. Future research should consider surface pressure and flowfield measurements, significantly higher Reynolds numbers, and variable intracycle flap deflection mechanisms to optimize performance and minimize unsteady loads.

Investigating the effect of axial fan shrinkage obtained by centrifugal casting technology on aerodynamic characteristics

Centrifugal casting technology was developed for the application of manufacturing axial fans. In the literature, these fans were usually manufactured by injection molding, mechanical processing or heat pressing. The main characteristic of this molding technology allows the creation of thick and hollow blades. This characteristic of the blades gives useful advantages of the fan that cannot be achieved by conventional methods. The centrifugal casting technology has been applied to fabricate axial fans in recent research. However, the issue of quality control and especially the shrinkage of the resulting fan compared to the molding has not yet been considered. Therefore, more in-depth studies and approaches are required. In this study, 3D scanning method is used to evaluate the shrinkage of the blades. The used 3D scanner is the Comet L3D 5M type based on structured light (blue LED) with a 5-megapixel sensor. This device achieves high accuracy and reliability (resolution 18 μm). The theoretical basis for determining fan shrinkage compared to CAD molds is based on the following main parameters: Chord line L (mm), relative thickness Emax (%), and stagger angle ( (degrees). In addition, the aerodynamic characteristics of the proposed fan are compared to those of a fan made of aluminum (blades are identical, but different in fabricating technology). Characteristics of this aluminum rigid-fan are assumed as reference. The results showed that the difference was not large between the blades. Besides, the results of aerodynamic testing on the test bench of the two fans are almost similar. This indicates the good adaptability of the axial fan received by the centrifugal casting technology.

Nonlinear shape analysis for constructional multiwire cable structures with clamps considering multi-stiffness properties

Multiwire cable structures equipped with clamps are widely used in civil engineering, such as suspension bridges, and their bending stiffness is always neglected in design. However, in practice, bending can be important locally when the sudden changes of cable curvature occur due to hanger forces loaded group by group during construction. Moreover, the main cable, composed of high-strength steel wires, has a secondary sectional bending stiffness that changes and with its tension state, being small (flexible) at the first stages and increasing gradually until reaching a notable rigidity (stiff). This, along with the effect of clamps leads to a Flexible-Stiff Coupling Multi-stiffnesses (FSCM) properties with geometrical and mechanical nonlinearities. Ignoring this might introduce uncontrollable shape errors during installation. To fill the gap of a shape analysis considering the FSCM, an analytical method as Chord Substitution Method (CSM) is proposed. The chord line geometry of the structure is taken as an independent object, and then the system equilibrium can be represented with a set of chain pole equations based on an established physic model of cable segment. The extension of each chord rod is modeled with a composite-chord-spring considering both axial and bending geometric stiffnesses. The cable curvature effect at clamps can be modeled by correcting external forces to satisfy a bending compatibility condition. The effectiveness of the CSM is validated by a previous model test found in the literature, and a real example is used for comparative studies. This method might be promising for a refined construction design and monitoring control of such structures.

Verification of the self-starting problem of a Vertical Axis Wind Turbine with Inclined Blades

In this paper, a theoretical investigation of the impact of varying the blade inclination angle b on the power coefficient of vertical-axis wind turbines equipped with straight blades has been demonstration, where the inclination angle was modified from twenty-five degrees to eighty-five degrees. Within the framework of this study, the term SS-VAWT was assigned to refer to the rotor which is the subject of the research. The "Multi Stream Tube-MST" mathematical model was used after some of its equations were modified to be consistent with the geometrical shape of the SS-VAWT rotor. A computer program was designed using the "Microsoft Visual Basic" programming language as an application of the mathematical model used, which led to the effectiveness of this program and compared its final results with previous experimental results from other studies, this work was carried out on twelve obligatory SS-VAWT, which are classified into four namely H group which is characterized by rotor high change effect, R group which is characterized by diameter effect, N group which is characterized by number of blades effect and C group influenced by the length of blade chord line. The results are represented by power curves as a function of tip speed ratio. The behavior of the curves for each case was verified and compared to determine the optimum case. All results were taken in the small range of tip speed ratio λ0 extending from 0 to 2.8. Since the Cp coefficient and the λ0 coefficient are dimensionless values, the results can be applied to large-sized air rotors, provided that there is geometric similarity. Because they found that the feather's 45-degree tilt and location reduce the problem of starting self-motion.

Inviscid modeling of unsteady morphing airfoils using a discrete-vortex method

Abstract A low-order physics-based model to simulate the unsteady flow response to airfoils undergoing large-amplitude variations of the camber is presented in this paper. Potential-flow theory adapted for unsteady airfoils and numerical methods using discrete-vortex elements are combined to obtain rapid predictions of flow behavior and force evolution. To elude the inherent restriction of thin-airfoil theory to small flow disturbances, a time-varying chord line is proposed in this work over which to satisfy the appropriate boundary condition, enabling large deformations of the camber line to be modeled. Computational fluid dynamics simulations are performed to assess the accuracy of the low-order model for a wide range of dynamic trailing-edge flap deflections. By allowing the chord line to rotate with trailing-edge deflections, aerodynamic loads predictions are greatly enhanced as compared to the classical approach where the chord line is fixed. This is especially evident for large-amplitude deformations. Graphical abstract

Wind tunnel experimental study of aerodynamic characteristics of co-flow jet wing with built-in air source

To further investigate the aerodynamic characteristics and control mechanisms of co-flow jet wings, this study presents the design of a co-flow jet wing (CFJ-CLARKY18) with an embedded micro centrifugal compressor. The CFJ-CLARKY18 wing, based on the CLARKY18 airfoil, incorporates a miniature centrifugal compressor positioned horizontally within the wing's cavity, with its rotor axis perpendicular to the wing chord line, thus alleviating geometric constraints and the compressor's exhaust swirl. The integration of the co-flow jet device with the wing is achieved through a split-flow channel design to ensure uniform co-flow jet injection, followed by verification of jet uniformity and calibration of six jet momentum coefficients. Subsequently, static and dynamic control experiments of the co-flow jet wing are conducted in an open-return wind tunnel, utilizing force measurement systems and high-speed particle image velocimetry tools to investigate its aerodynamic characteristics and control mechanisms. Static stall tests indicate that, compared to the original wing, the CFJ-CLARKY18 wing exhibits a significant increase in lift and a noticeable delay in stall angle. At low angles of attack, an increase in co-flow jet momentum leads to a reduction in drag coefficient, with the possibility of achieving negative drag (thrust) even at high co-flow jet momentum coefficients. The results of dynamic stall tests with force measurements indicate that, while keeping the reduced frequency constant, an increase in co-flow jet momentum coefficient results in higher maximum lift and average lift coefficients, accompanied by a significant reduction in average drag coefficient and the hysteresis loop area of the lift coefficient. Despite the increased reduced frequency exacerbating the wing's stall effect, the stall effect weakens significantly once the co-flow jet momentum coefficient is increased.

Detection and identification of Devibursaphelenchus minor sp. n. isolated in the bark from the USA

Summary Bark in an empty container from the USA was inspected in Ningbo port, China, and a Devibursaphelenchus population was detected. It was processed and identified as Devibursaphelenchus minor sp. n. The new species is characterised by the lateral field with three incisures, female stylet tripartite, 13.9 (12.7-14.6) μm long without basal thickenings, secretory-excretory pore at the same level as nerve ring or slightly posterior, vagina not sclerotised, vulval lips slightly protruding and vulval flap absent. Post-vulval uterine sac (PUS) not well developed, very short and obscure, extending for half vulval body diam. long, anus and rectum indistinct or absent. Posterior body region conical elongated, gradually narrowing, slightly ventrally curved, ending with a bluntly pointed terminus. Male rare, the spicules are arcuate, separate, 8.2 μm along the chord line, with well-developed condylus, triangular rostrum with finely rounded tip, cucullus or apophysis absent. Tail conical, dorsally convex, ventrally slightly concave with bluntly pointed terminus, ventral bursa not confirmed. Two pairs of genital papillae present. It differs from all other species in this genus by extremely short body length of females and males. Molecular phylogenetic analyses based upon rRNA D2-D3 sequences confirmed it as a new species.

Effect of Vortex Generators on Airfoil NACA 632-415 to Aerodynamic Characteristics Using CFD

To determine the aircraft’s flight performance, the airfoil type must be considered when designing the wing. A vortex can form when the airfoil travels through a fluid stream with a difference in velocity and pressure around it. Airfoil modification is carried out to delay the occurrence of flow separation by adding a vortex generator. This paper discusses how adding the vortex generator helps slow the stall’s onset and how the vortex generator affects the fluid flow and aerodynamic forces acting on the NACA 632-415. The vortex generator profile is positioned at an x/c = 20% of the chord line’s direction from the leading edge. The variation used is an airfoil’s angle of attack (α). Some parameters to be evaluated include the coefficient lift force (C­­L), the coefficient drag force (CD), and the gliding ratio (C­­L/CD). The research was conducted by the CFD method based on the angle of attack that produces the coefficient lift and drag forces. The addition of the vortex generator can delay the flow separation, increase the lift force coefficient by about 24.9%, the drag force coefficient by about 2.7%, and the gliding ratio by 9.1%.

Quasi-Steady Simulation of Glaze Ice Accretion and Heat Transfer in the Supercooled Large Droplet Regime in Atmospheric Turbulent Air Flow

Abstract To avoid the use of a computationally intensive full unsteady simulation while providing an accurate solution, a quasi-steady simulation has been performed to study glaze and mixed ice accretion in the supercooled large droplet (SLD) regime in turbulent flow of atmospheric air. We have attempted to find the minimum time-step necessary to adequately simulate the icing process on an airfoil surface. Based on node displacement, a mesh morphing scheme has been adopted in the computations to account for the moving boundaries that are caused by the continuous ice buildup. We have modeled ice accretion on an airfoil surface for a time period of 232 s using several time steps. At each time-step we solved the steady-state conservation equations for the air and droplet phases and then used the results as initial conditions for the next time position. The magnitude of the time-step ranged from a least accurate two-shot simulation (where the time-step is 116 s) to a most accurate 2320-shot simulation (where the time-step is 0.1 s). In-between these two extreme time steps, we have performed a three-shot simulation (where the time-step is 77.33 s), a four-shot simulation (where the time-step is 58 s), a six-shot simulation (where the time-step is 38.67 s), a 46-shot simulation (where the time-step is 5 s), and a 232-shot simulation (where the time-step is 1 s). We have done so to find out the degree of accuracy (or inaccuracy) of the multishot simulation approach and to find out the appropriate time-step needed for a successful and valid quasi-steady simulation. A valid quasi-steady simulation needs to use a time-step that is small enough to reproduce the full time-dependent solution within a very small error band. We have found that both the 1 s and the 0.1 s time steps produce virtually identical results. This is the primary litmus test that proves the validity of the quasi-steady-state assumption. The results adopted in this paper are thus all based on the more conservative 0.1 s time-step. In the process of performing the simulations, remeshing was required in order to maintain the grid density in zones of high curvature to be able to capture the full physics in those zones. After successfully modeling glaze ice accretion over the airfoil surface using the 0.1 s quasi-steady simulation approach, the effects of supercooled large droplets (SLDs) impacting the surface have been examined and presented in terms of the variation of the local collection efficiency, the water film thickness, and the heat transfer rate. Examination of the variation of the angle that the ice horn makes with the airfoil chord line demonstrated a 20% improvement in angle prediction when the time-step is reduced from 116 s to 0.1 s. The analysis also reveals a 12% or 8.5% increase in the maximum collection efficiency, βmax, depending on whether the value of the liquid water content (LWC) has been doubled from 0.5 g/m3 to 1 g/m3, or the value of the freestream velocity has been doubled from 75 m/s to 150 m/s, respectively. Because of the need to monitor the local collection efficiency and convective heat fluxes at each shot (regardless of the number of shots employed), the approach adopted here was found to be effective in successively and successfully reproducing the curvature of the glaze ice horn.

Integrated Aerodynamic and Structural Blade Shape Optimization of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants

Abstract Within this study, the blade shape of a large-scale axial turbine operating with sCO2 blended with dopants is optimized using an integrated aerodynamic-structural three-dimensional (3D) numerical model, whereby the optimization aims at maximizing the aerodynamic efficiency whilst meeting a set of stress constraints to ensure safe operation. Specifically, three candidate mixtures are considered, namely, CO2 blended with titanium tetrachloride (TiCl4), hexafluorobenzene (C6F6), or sulfur dioxide (SO2), where the selected blends and boundary conditions are defined by the EU project, SCARABEUS. A single passage axial turbine numerical model is setup and applied to the first stage of a large-scale multistage axial turbine design. The aerodynamic performance is simulated using a 3D steady-state viscous computational fluid dynamic (CFD) model while the blade stress distribution is obtained from a static structural finite element analysis simulation (FEA). A genetic algorithm is used to optimize parameters defining the blade angle and thickness distributions along the chord line while a surrogate model is used to provide fast and reliable model predictions during optimization using a genetic aggregation response surface. The uncertainty of the surrogate model, represented by the difference between the surrogate model results and the CFD/FEA model results, is evaluated using a set of verification points and is found to be less than 0.3% for aerodynamic efficiency and 1% for both the mass-flow rate and the maximum equivalent stresses. The comparison between the final optimized blade cross section has shown some common trends in optimizing the blade design by decreasing the stator and rotor trailing edge thickness, increasing the stator thickness near the trailing edge, and decreasing the rotor thickness near the trailing edge and decreasing the rotor outlet angle. Further investigations of the loss breakdown of the optimized and reference blade designs are presented to highlight the role of the optimization process in reducing aerodynamic losses. It has been noted that the performance improvement achieved through shape optimization is mainly due to decreasing the endwall losses with both the stator and rotor passages.

Numerical Investigation of the Effect of Trailing Edge Shape on Surface-Piercing Propeller Performance

One of the main challenges in the development of surface-piercing propellers is to identify the effects of geometric parameters on the performance. The main geometric difference between SPP and conventional propellers is its blade section shape. The blade section is of super cavity type with a sharp leading edge and thick trailing edge. The geometry of this propeller is mostly designed experimentally, and comprehensive studies have not been performed to examine its parameters. Therefore, this research aims to investigate the effect of trailing edge shape on ventilation cavity development and SPP performance. The performance of a series of HL-tx propellers consisting of 6 propellers with different trailing edge shapes has been studied numerically. Numerical simulation of geometries was performed using URANS method coupled with the VOF method to capture the interface of fluids. The sliding mesh technique was also used to simulate the rotation of SPPs in transition mode. The results of the simulation method are in good agreement with the experimental data. As the results indicated, there was a 40% change in thrust and torque coefficients due to the trailing edge shape changes, which is a significant effect. However, changes in efficiency are about 7%. Meanwhile, the results revealed SPPs with a larger angle to the chord line and shorter height have better performance and ventilation cover behind the blade.

Identification of the geometric design parameters of propeller blades from 3D scanning

This paper presents a new method for the identification of geometric design parameters of ISO 484 class propeller blades from scanned point cloud data. The method can be used for tolerance inspection and in-line measurement of manufactured blades, and for wear assessment and reverse engineering of propellers in service. The geometry of the propeller blades is specified by a set of blade sections stacked radially on concentric cylindrical surfaces. For each of these sections, the chord line and mean camber line is determined, and geometric design parameters such as the pitch, skew, chord length, camber, and thickness distributions are identified. The proposed method is a complete procedure for identifying the design parameters of marine propeller blades from point cloud data, and includes a novel method for the precise identification of the mean camber line based on Voronoi diagrams and Delaunay triangulation. The paper includes validation of the proposed method in experiments where reverse engineering is applied to a propeller blade of the KVLCC2 propeller, and in 3D scanning of a large, high-skew thruster blade where the results were compared to CMM measurements.

Parameterizing Airfoil Shape Using Aerodynamic Performance Parameters

A novel shape parameterization for airfoils (named as PAERO) is proposed to provide design variables related to the aerodynamic characteristics based on the linearized aerodynamic theory. The idea is inspired by the classical thin airfoil theory. Instead of describing the airfoil geometry explicitly, the mean camber line of an airfoil can be implicitly defined by the vortex distribution on the chord line that is expressed by a Fourier series in the thin airfoil theory. The Fourier series is parameterized by the Fourier coefficients specified by users. Within the frame of linearized aerodynamic theory, the first three Fourier coefficients are determined by the angle of attack, lift coefficient, and pitching moment coefficient, naturally providing three aerodynamic performance parameters. Then, the airfoil shape parameterization is completed by further parameterizing the thickness distribution by either the Class-Shape-Transformation method or the B-splines, depending on the specific applications. The test results show that the proposed shape parameterization has the same ability of fitting the existing airfoils as the traditional Class-Shape-Transformation method, but providing more aerodynamic performance parameters that are proved to be highly useful in applications.

Simulating NACA Equations Used in Optimizing Wind Turbine Blade Design

Aerodynamic scientists are interested in geometry definition and possible geometric shapes that would be useful in design. This paper illustrates a simulation of a NACA four digits airfoil blade profile using MATLAB. As airfoil design became more sophisticated, this basic approach has been modified to include additional variables, and suggestions for the chord line length at the root and at the end of the blade. as well as changes in the twisting angle of the blade and its thickness, this helps to reduce the weight of the blade significantly Simulating NACA equations is very useful in obtaining coordinates of airfoil curvature for the whole series of NACA four digits, which is very effective in optimizing blade design. In order to get an optimal operating performance and high efficiency for the airfoil, the blade surface must be smooth and does not suffer any discontinuities or undefined cases, which cause separation of the boundary layer during the airflow, and get as a result great energy losses. Therefore, the conditions for the continuity of the blade was extracted using mathematical analysis, so the air flow does not suffer any interruptions which reduce the efficiency. This enable us to determine the locations of the maximum thickness of the blade sections on the chord along the blade, in addition to specifying conditions for the chord line length at the root and at the end of the blade which keep the blade curvature continuous and doesn’t have any irregular points, which also facilities writing the necessary programs.

Experimental studies of turbulent pulsating flow and heat transfer in a serpentine channel with winglike turbulators

Particle Image Velocimetry and Infrared Thermography measurements are applied to explore the effect of quasi-triangular pulsatile flow inlet on active thermal-fluidic performance in a serpentine channel with innovative winglike turbulators. The novel turbulators are mounted in-line on two sidewalls of the channel with the attack angle (α), thickness to chord line ratio (t/C), and pitch to the channel hydraulic diameter ratio (Pi/DH) respectively fixed at 20°, 0.2, and 0.7. The Strouhal number (St) varies from 0 to 0.67 at a fixed Reynolds number (Re) of 10,000. Relative to the steady-state case (St = 0), the flow pulsation not only strengthens the Fujiwhara co-rotating vortices but also eliminates the corner vortex streams, leading to the overall Nusselt number (Nu¯/Nuo) enhancement by 13%. Moreover, both the Nu¯/Nuo and friction factor (f¯/fo) reveal the tilde-like trends with St, resulting in the highest Nu¯/Nuo of 5.2 and thermal performance factor of 1.39 at St = 0.67, which are higher than the previous best results for 10≤f¯/fo≤100 in the Nu¯/Nuo-f¯/fo diagram. Finally, by combing the present data with our previous steady state results, composite correlations of Nu¯/Nuo and f¯/fo versus Re, α, t/C, Pi/DH, and St are proposed.

Drag Reduction Using Biomimetic Sharkskin Denticles

This paper explores the use of sharkskin in improving the aerodynamic performance of aerofoils. A biomimetic analysis of the sharkskin denticles was conducted and the denticles were incorporated on the surface of a 2-Dimensional (2D) NACA0012 aerofoil. The aerodynamic performance including the drag reduction rate, lift enhancement rate, and Lift to Drag (L/D) enhancement rate for sharkskin denticles were calculated at different locations along the chord line of the aerofoil and at different Angles of Attack (AOAs) through Computational Fluid Dynamics (CFD). Two different denticle orientations were tested. Conditional results indicate that the denticle reduces drag by 4.3% and attains an L/D enhancement ratio of 3.6%.

The very high n Rydberg series of Ar16+ in Alcator C-Mod tokamak plasmas

X-ray transitions of the very high-n Rydberg series in Ar16+ have been observed from Alcator C-Mod tokamak plasmas. Individual emission lines up to 1s16p-1s2 have been resolved and the central chord line brightnesses with principal quantum number n between 7 and 16 are generally found to decay as 1/n α , with α slightly larger than 3. In the plasma periphery, emission from 1s9p-1s2 and 1s10p-1s2 are found to be significantly enhanced relative to this decrease, indicative of selected population of these levels through charge exchange between background neutral deuterium in the ground state and Ar17+. An unresolved feature between the wavelengths of 1s27p-1s2 and 1s30p-1s2 is also present, which arises through charge exchange with neutral deuterium in the n* = 3 excited state. The brightnesses of transitions populated by charge exchange are spatially up/down asymmetric, with an excess on the side of the magnetic surface X-point. The relative brightness of the unresolved very high-n feature compared to 1s7p-1s2 is found to increase with electron temperature and decrease with electron density. Simulations of line emission just on the long wavelength side of the Ar16+ ionization limit indicate that the principal quantum number decay exponent is closer to α = 4 at very high n. The brightness dependence on n below 16 is in excellent agreement with calculations from the flexible atomic code package.

Influence of the pivot location on the thrust and propulsive efficiency performance of a two-dimensional flapping elliptic airfoil in a forward flight

In this article, the effect of the pivot point location on the thrust performance of a two-dimensional sinusoidal flapping elliptic airfoil in a forward flight condition is investigated using numerical simulations and in-house water tunnel experiments. On the chord line, three different pivot locations at a distance of 0.25c, 0.5c, and 0.75c from the leading edge of the airfoil are considered, where c is the chord length of the airfoil. The flapping frequency and effective angle of attack are varied to investigate the propulsive performance of the airfoil at a Reynolds number of 5000. It is noticed that a modification in the pivot location significantly influences the linear velocity distribution, the evolution of the leading-edge vortex, and the near wake region on the airfoil. Consequently, both the transient and time-averaged thrust coefficient of the flapping airfoil is considerably affected. In addition, we have observed when the flapping frequency is increased, the time-averaged thrust coefficient of the airfoil tends to increase up to a critical Strouhal number and deteriorates thereafter. The same trend of time-averaged thrust coefficient is seen at all considered pivot locations and effective angle of attacks. Our finding suggests, at the high flapping frequency, the formation of rotation induced adverse suction region around the airfoil and delay in the shedding of the leading edge vortex developed in the previous flapping stroke are the primary sources, attributing to the thrust deterioration of the flapping airfoil with symmetric pivot location 0.5c. On the other hand, the thrust degrading effects at the two asymmetric pivot locations, 0.25c and 0.75c, are triggered by the adverse suction regions induced by asymmetric airfoil-surface velocity distribution as well as airfoil-wake vortices interaction. Moreover, the thrust degradation can be postponed to a higher critical Strouhal number if the airfoil pivot location is set near the leading edge and higher amplitude of effective angle of attack is followed. Besides, we found that the airfoil propulsive efficiency is affected due to a change in the aerodynamic power co-efficient with the modification of the pivot location. Furthermore, our observation concludes that the pivot location at 0.25c from the leading edge has maximum time-averaged thrust and propulsive efficiency performances at least for the range of pivot locations, flapping frequencies, and effective angle of attacks examined here.