NACA0012 Foil Research Articles

Self-Propulsive Property of Flexible Foil Undergoing Traveling Wavy Motion: A Numerical Investigation

The propulsive characteristics of self-propelling 3D flexible foil are numerically studied. Two kinds of dynamic boundary techniques, namely the dynamic mesh technique and overlapping mesh technique, are used to realize the self-propulsion of flexible foil. The effects of aspect ratio (AR), characteristic thickness (d), and section shape on propulsive characteristics are numerically studied. Results demonstrate that the moving velocity increases monotonically with the consistent growth of AR, and a linear relationship is found between them. The peak value of propulsive efficiency can be acquired when AR = 1.0. Moreover, the growth of d shall produce a negative effect on moving velocity. It is suggested that the value of d should be smaller than 0.15 for the sake of acquiring high propulsive efficiency. As for the section shape effect, the foil with a rectangular shape presents the worst propulsive property, while the NACA0015 foil exhibits the best one. Furthermore, the typical vortex structures are also exhibited and analyzed. The conclusions acquired in this study are of great significance for designing a bionic underwater vehicle.

Optimal propulsion efficiency for NACA0012 foils with asymmetries in motion: A hybrid approach using the Taguchi method and artificial neural networks

This study uses the Taguchi method and artificial neural networks to optimize the thrust and propulsion efficiency of a NACA0012 foil, examining variables like downstroke duration (S = 0.3–0.5), angle of attack during downstroke and upstroke (αmd, αmu = 20°–50°), and Strouhal number (St = 0.2–0.5). Analysis shows that the St greatly affects thrust, while the αmu is pivotal for propulsion efficiency. Thrust is optimized by using a shorter S of 0.3, a greater αmd of 50° and a larger St of 0.45–0.5 and efficiency is optimized by using symmetric S of 0.5, a smaller αmd, αmu of 20° and a lower St of 0.35–0.39. Force and flow field analysis shows that certain combinations optimize thrust by mitigating negative thrust in the early downstroke, though they increase power consumption, lowering overall efficiency. Configurations balancing stroke duration and minimizing the angle of attack enhance efficiency by decreasing power demand for steady thrust. Wake structure analysis reveals that optimal efficiency involves generating reverse Kármán vortex streets, while optimizing thrust leads to a more chaotic wake. This study advances fluid dynamics in propulsion systems and aids in designing more efficient, adaptable underwater vehicles by identifying the key balance between thrust optimization and propulsion efficiency.

The propulsion performance of the semi-active tandem flapping foils for wave gliders: A study on vortex interactions and hydrodynamic performance

An investigation is conducted on the propulsion performance of semi-active flapping foils in tandem configuration of the wave glider, considering different vortex effects and tandem distances. The Finite Volume Method is utilized with commercial CFD software Fluent to solve the URANS equations around the flapping foil. A mesh comprising a 2D NACA0012 foil with Reynolds number Re = 42,000 is used in all simulations. The study investigates the propulsion performance of tandem flapping foil systems, focusing on the differing impacts of wave interaction on the front and rear foils. It explores how varying tandem distances and reduced frequencies influence thrust enhancement and degradation. The research reveals that while the front foil consistently benefits from thrust enhancement, the rear foil's performance is more complex, being subject to thrust enhancement or reduction due to wake vortex interactions. Detailed analyses of instantaneous thrust coefficients, pitching trajectories, and pressure contours provide insights into the hydrodynamic performance of these systems. The findings emphasize the importance of synchronization in motion between the foils for optimal propulsion and highlight the rear foil's susceptibility to changes in the wake flow, affecting its thrust generation capability. Thus, the optimal tandem distance can fully capitalize on the thrust enhancement effect of the wake interaction to improve the performance of the tandem flapping foil propulsion system.

An efficient parameter-retrieval-based surrogate-assisted optimization of on-platform honeycomb absorbing structures

An electromagnetic parameter-retrieval-based surrogate-assisted optimization (PSAO) algorithm is presented to reduce radar cross section (RCS) by optimizing the on-platform honeycomb absorbing structures. To facilitate the optimization process, the honeycomb structure is transformed to an anisotropic homogeneous slab, and the effective parameters of the slab are extracted by the retrieval algorithm. A multi-fidelity model is employed to reduce the computing-time consumption, in which a Gaussian process (GP) regression model is used as the substitute for the coarse model. The GP model establishes a relationship between the geometry of the honeycomb structure and the RCS response of the target coated with the equivalent slab. Finally, the optimization result of the fine model is achieved through a space mapping strategy. The accuracy of the parameter extraction algorithm is verified by analyzing the honeycomb absorbing structure. Subsequently, the proposed optimization method is applied to a metal plate and a metal cylinder, resulting in a 10 dB reduction of RCS in broadband and wide-angle scenarios. This demonstrates the applicability of the proposed PSAO algorithm to both planar and conformal on-platform honeycomb absorbing structures. Furthermore, an NACA0015 foil is analyzed, showing an average RCS reduction of 10 dB and a minimum RCS reduction of 5 dB in the X-band. These results indicate that the PSAO approach can effectively apply to complicated targets. Additionally, the proposed method exhibits significant advantages in terms of computational accuracy and efficiency compared to the traditional genetic algorithm.

Aerodynamic and aeroacoustic performance of a pitching foil with trailing edge serrations at a high Reynolds number

The aerodynamic and aeroacoustic performance of a low-aspect-ratio (AR=0.2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {AR}=0.2$$\\end{document}) pitching foil during dynamic stall are investigated numerically with focus on the effects of trailing edge serrations. A hybrid method coupling an immersed boundary method for incompressible flows with the Ffowcs Williams–Hawkings acoustic analogy is employed. Large eddy simulation and turbulent boundary layer equation wall model are also employed to capture the turbulent effects. A modified NACA0012 foil with a rectangular trailing edge flap attached to the trailing edge (baseline case) undergoing pitching motion is considered. Trailing edge serrations are applied to the trailing edge flap and their effects on the aerodynamic and aeroacoustic performance of the oscillating airfoil are considered by varying the wave amplitude (2h∗=0.05,0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2h^*= 0.05, 0.1$$\\end{document}, and 0.2) at a Reynolds number of 100,000 and a Mach number of 0.05. It is found that the reduction of the sound pressure level at the dimensionless frequency band Stb∈[1.25,4]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$St_{b}\\in [1.25,4]$$\\end{document} can be over 4 dB with the presence of the trailing edge serrations (2h∗=0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2h^*=0.1$$\\end{document}), while the aerodynamic performance and its fluctuations are not significantly altered except a reduction around 10% in the negative moment coefficient and it fluctuations. This is due to the reduction of the average spanwise coherence function and the average surface pressure with respect to that of the baseline case, suggesting the reduction of the spanwise coherence and the noise source may result in the noise reduction. Analysis of the topology of the near wake coherent structure for 2h∗=0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2h^*=0.1$$\\end{document} reveals that the alignment of the streamwise-oriented vortex with the serration edge may reduce the surface pressure fluctuation.Graphical abstract

Numerical Study of Resistance Trimaran Unmanned Surface Vehicle Based on NACA Foil

Unmanned Surface Vehicles (USVs) are used to monitor territorial waters and collect sea data, including hydrographic and oceanographic data. Compared with larger survey vessels, USVs are more flexible and cost-efficient because of their compact form. The latest USV design uses NACA foil as a trimaran hull form with a self-maneuvering system. This design must provide minimal resistance for longer durability during operation. In this study, the authors investigated the relationship between the distance, angle of attack, and shape of the NACA foil as a USV trimaran hull to reduce the resistance. The analysis began with verification and validation based on previous experimental research. Several configurations of the positions of each hull were modelled using an angle of attack of up to 20 °. Computational Fluid Dynamics (CFD) analysis was employed in ANSYS CFX to simulate the model. After obtaining the optimal configuration, variations in the NACA foil on the hull were performed, and the simulation was repeated. The study found that the configuration without an angle of attack, with one hull positioned in front and two hulls positioned behind, using NACA 0024 produces the smallest resistance value. Furthermore, this configuration exhibited wave interference with smaller volume-fraction contours. The study concludes that the angle of attack results in greater resistance owing to the shorter distance between the NACA foils. This research provides insight into the trimaran design of USVs and contributes to the further development of marine robotics technology and unmanned surface vehicles.

Paleomass for R-bracketing body volume of marine vertebrates with 3D models.

Body mass is arguably the most important characteristic of an organism, yet it is often not available in biological samples that have been skeletonized, liquid-preserved, or fossilized. The lack of information is especially problematic for fossil species, for which individuals with body mass information are not available anywhere. Multiple methods are available for estimating the body mass of fossil terrestrial vertebrates but those for their marine counterparts are limited. Paleomass is a software tool for estimating the body mass of marine vertebrates from their orthogonal silhouettes through bracketing. It generates a set of two 3D models from these silhouettes, assuming superelliptical body cross-sections with different exponent values. By setting the exponents appropriately, it is possible to bracket the true volume of the animal between those of the two models. The original version phased out together with the language platform it used. A new version is reported here as an open-source package based on the R scripting language. It inherits the underlying principles of the original version but has been completely rewritten with a new architecture. For example, it first produces 3D mesh models of the animal and then measures their volumes and areas with the VCG library, unlike the original version that did not produce a 3D model but instead computed the volume and area segment by segment using parametric equations. The new version also exports 3D models in polygon meshes, allowing later tests by other software. Other improvements include the use of NACA foil sections for hydrofoils such as flippers, and optional interpolation with local regression. The software has a high accuracy, with the mean absolute errors of 1.33% when the silhouettes of the animals are known.

Self-propulsion characteristics of fish-like undulating foil – a numerical investigation

ABSTRACT In this work, the propulsive characteristic of an auto-propelled 2D NACA0015 foil undergoing traveling wave motion is numerically investigated. The effects of typical motion parameters, i.e. traveling amplitude, traveling frequency (f), and geometric parameters (thickness, d) on the propulsive property of auto-propelled foil are systematically investigated. The numerical results reveal that the moving velocity of foil can be significantly enhanced by the enlargement of the traveling amplitude and traveling frequency, while it presents a sharp decrease when the foil thickness increases. As for the propulsive efficiency, the effects of a 1, f and d on the magnitude of η are similar to each other, that is, the magnitude of η will ascend to the peak value and then decrease, and there exists an optimum value corresponding to the highest magnitude of η. The flow structures in the wake of the auto-propelled foil under typical calculation conditions are also analysed.

Modeling and Analysis of the Leading-Edge Vortex on Flapping Foil Turbines in Swing-Arm Mode

AbstractHydrokinetic flapping foil turbines in swing-arm mode have gained considerable interest in recent years because of their enhanced capability to extract power, and improved efficiency compared to foils in simple mode. The performance of foil turbines is closely linked to the development and separation of the leading-edge vortex (LEV). The paper's aim is to develop a purpose-built 2D numerical model to present the capability of integrating the weighted residual finite element method (FEM) with the interface capturing technique, level-set method (LSM), in providing a high-quality numerical simulation of the flapping foil in swing-arm mode, by accurately modeling the formation and the separation of the LEV on flapping foils. The solvers were validated against well-known static and dynamic benchmark problems and the effect of the mesh density was analyzed and discussed. This paper further covers an initial investigation of the hydrodynamics of flapping foil in swing-arm mode, by studying the structure of the vortex around a NACA0012 foil. The presented method helps to provide a better understanding of the relation between the Leading-Edge Vortex creation, growth, and separation over the flapping foil in swing-arm mode and the extracted power from a hydrokinetic turbine.

Kinematic Optimization of Energy Extraction Efficiency for Flapping Airfoil by using Response Surface Method and Genetic Algorithm

In this paper, numerical simulations have been performed to study the performance of a single fully activated flapping wing serving as energy harvester. The aims of the paper are predicting and maximizing the energy extraction efficiency by using optimization methodology. The metamodeling and the genetic algorithms are applied in order to find the optimal configuration improving the efficiency. A response surface method (RSM) based on Box–Behnken experimental design and genetic algorithm has been chosen to solve this problem. Three optimization factors have been manipulated, i.e. the dimensionless heaving amplitude h0, the pitching amplitude θ0 and the flapping frequency f. The ANSYS FLUENT 14 commercial software has been used to compute the governing flow equations at a Reynolds number of 1100, while the flapping movement combined from heaving and pitching of the NACA0015 foil has been carried out by using an in house user-defined function (UDF). A maximum predicted efficiency of 34.02% has been obtained with high accuracy of optimal kinematic factors of dimensionless heaving amplitude around the chord, high pitching amplitude and low flapping frequency of 0.304 hertz. Results have also showed that the interaction effect between optimization factors is important and the quadratic effect of the frequency is strong confirming the great potential of the applied optimization methodology.

Hybrid Lattice-Boltzmann-Potential Flow Simulations of Turbulent Flow around Submerged Structures

We report on the development and validation of a 3D hybrid Lattice Boltzmann Model (LBM), with Large Eddy Simulation (LES), to simulate the interactions of incompressible turbulent flows with ocean structures. The LBM is based on a perturbation method, in which the velocity and pressure are expressed as the sum of an inviscid flow and a viscous perturbation. The far- to near-field flow is assumed to be inviscid and represented by potential flow theory, which can be efficiently modeled with a Boundary Element Method (BEM). The near-field perturbation flow around structures is modeled by the Navier–Stokes (NS) equations, based on a Lattice Boltzmann Method (LBM) with a Large Eddy Simulation (LES) of the turbulence. In the paper, we present the hybrid model formulation, in which a modified LBM collision operator is introduced to simulate the viscous perturbation flow, resulting in a novel perturbation LBM (pLBM) approach. The pLBM is then extended for the simulation of turbulence using the LES and a wall model to represent the viscous/turbulent sub-layer near solid boundaries. The hybrid model is first validated by simulating turbulent flows over a flat plate, for moderate to large Reynolds number values, Re ∈[3.7×104;1.2×106]; the plate friction coefficient and near-field turbulence properties computed with the model are found to agree well with both experiments and direct NS simulations. We then simulate the flow past a NACA-0012 foil using a regular LBM-LES and the new hybrid pLBM-LES models with the wall model, for Re = 1.44×106. A good agreement is found for the computed lift and drag forces, and pressure distribution on the foil, with experiments and results of other numerical methods. Results obtained with the pLBM model are either nearly identical or slightly improved, relative to those of the standard LBM, but are obtained in a significantly smaller computational domain and hence at a much reduced computational cost, thus demonstrating the benefits of the new hybrid approach.

Effect of superhydrophobicity on the wake of a pitching foil across various Strouhal numbers

Particle image velocimetry-based measurements have been performed to study the flow over a pitching superhydrophobic NACA—National Advisory Committee for Aeronautics—0012 foil (SphNACA0012 foil) and to compare the same with NACA0012 foil. This is perhaps the first experimental study on a pitching SphNACA0012 foil. The objective is to understand the effects of superhydrophobicity on NACA0012 foil pitching about its leading edge at various Strouhal numbers, St = 0.08–0.65, with a constant pitching amplitude, θ0 = 4°, and Reynolds number, Re = 2400. Superhydrophobicity is found to significantly affect three different flow regimes: 2S von-Ka´rma´n wake, symmetric wake, and asymmetric wake regimes at smaller, intermediate, and larger values of St. In the 2S von-Ka´rma´n wake regime, although the wake structures of both the foils are quite comparable, a reduction in the shear layer strength and early rolling-up of vortices are observed for SphNACA0012 foil due to a partial slip effect. With a further increase in St, a transition to the symmetric wake regime is observed for both the foils and another transition that leads to a symmetry breaking of the vortex street is found to be earlier for SphNACA0012 foil, which results in the onset of lift generation at lower St than that of NACA0012 foil. The shear layer strength is weaker for the SphNACA0012 foil except at St = 0.24, which is a critical St for the jet deflection point and results in a 13% larger thrust coefficient for SphNACA0012 foils as compared to NACA0012 foils. These results on the larger lift as well as thrust coefficient at low St suggest improved maneuverability with high propulsive efficiency when superhydrophobicity is employed on the propulsor of underwater vehicles.

Energy extraction of oscillating foil with an active deflecting trailing-edge flap

The method of oscillating-foil energy extraction can be used to extract kinetic energy from the surrounding flow by a combined pitching and heaving motion of the foil. In order to improve the efficiency of energy extraction, a slotted foil with an active deflecting trailing-edge flap—inspired by the structure of the tail edge of bird wings—is designed. In this study, the unsteady Reynolds-averaged Navier–Stokes equation is solved to investigate the energy extraction performance of an oscillating foil at a Reynolds number of 5.0 × 105. In the numerical simulation, the dynamic overset mesh technology is used in order to ensure the accuracy and convergence of numerical solution. The effect of the deflecting motion of trailing-edge flaps on the efficiency of energy extraction is studied at a range of oscillating frequencies. In addition, the flow control mechanisms of slots on the oscillating foil are revealed by comparing the flow fields of the slotted foil and the NACA0015 foil. The result shows that active deflecting trailing-edge flaps can improve the efficiency of energy extraction over a wide range of oscillation frequencies. The active deflection of trailing-edge flaps increases the energy extraction efficiency of oscillating foils by 21.1% relative to conventional foils under a specific operating condition of oscillating frequency f* = 0.18. A detailed analysis of the flow fields indicates that the slot on the foil can suppress flow separation, while it has a negative effect on the attachment of leading-edge vortices. The deflecting trailing-edge flap enhances the heaving force. Therefore, the energy output and the efficiency of the oscillating foil are enhanced especially at the operating conditions of the oscillating foil without leading-edge vortex shedding.

Effects of free surface on a flapping-foil based ocean current energy extractor

We study numerically the effects of free surface on a flapping-foil based ocean current energy extractor. A two-dimensional NACA0015 foil, subjected to a coupled pitching and heaving motions, at a fixed Reynolds number of 900, and varied Froude numbers between 0 and 2, is considered. We fix the non-dimensional frequency at f∗ = 0.16 and pitching amplitude at θ0 = 75°. The previous studies suggested that an energy extracting efficiency up to 0.30 could be achieved in a single-phase fluid flow at these specific parameters. In the current study, as the free surface is considered, we report that both the submergence depth and Froude number affect the energy extracting efficiency. As the submergence depth increases from H = 1 to H = 20, for all the Froude numbers considered, the efficiency converges eventually to 33.7%, though slightly higher efficiencies can be observed when both the depth and Froude number are small. At a fixed submergence depth, the efficiency decreases monotonically with the increasing Froude number, which trend is more pronounced when the depth is small, i.e., the foil is very close to the free surface. It is apparently suggested that the free surface plays an unfavorable role in the energy harvesting efficiency, therefore the foil should be deployed with a sufficiently large distance from the free surface, particularly when it operates at high Froude numbers.

Numerical study of the propulsive performance of two-dimensional pitching foils at very high frequencies: scaling laws and turbulence effects

PurposeThis paper aims to analyze the propulsive performance of small-amplitude pitching foils at very high frequencies with double objectives: to find out scaling laws for the time-averaged thrust and propulsive efficiency at very high frequencies; and to characterize the Strouhal number above which the effect of turbulence on the mean values cannot be neglected.Design/methodology/approachThe thrust force and propulsive efficiency of a pitching NACA0012 foil at high reduced frequencies (k) and a Reynolds number Re = 16 000 are analyzed using accurate numerical simulations, both assuming laminar flow and using a transition turbulence model. The time-averaged results are validated with available experimental data for k up to about 12 (Strouhal number, St, up to 0.6). This study also compares the present numerical results with the predictions of theoretical models and existing numerical results. For a foil pitching about its quarter chord with amplitude α0 = 8o, the reduced frequency is varied here up to k = 30 (St up to 2), much higher than in any previous numerical or experimental work.FindingsFor this pitch amplitude, turbulence effects are found negligible for St ≲ 0.8, and affecting less than 10% to the time-averaged thrust coefficient for larger St Linear potential theory fails for very large k, even for the small pitch amplitude considered, particularly for the power coefficient, and therefore for the propulsive efficiency. It is found that St2 for large St, in agreement with recent models, and the propulsive efficiency decays as 1/k, in disagreement with the linear potential theory.Originality/valuePitching foils are increasingly studied as efficient propellers and energy harvesting devices. Their performance at very high reduced frequencies has not been sufficiently analyzed before. The authors provide accurate numerical simulations to discern when turbulence is relevant for the computation of the time-averaged thrust and efficiency and how their scaling with the reduced frequency is affected in relation to the laminar-flow predictions. This is relevant because some small-amplitude theoretical models predict high propulsive efficiency of pitching foils at very high frequencies over certain ranges of the structural parameters, and only very accurate numerical simulations may decide on these predictions.

Assessing the Impact of Membrane Deformations on Wing Sail Performance

Abstract The aim of this research is to quantify the membrane deformations and their impact on performance for a ribbed wing sail. A 1m x 0.8m rectangular planform NACA0012 foil was designed to replicate a single section of a wing-sail. Two foils were manufactured based on this geometry, one out of solid foam and one using a rib and membrane structure. These were tested in the R.J. Mitchell closed return 3.6 m x 2.5 m wind tunnel at the University of Southampton. Their aerodynamic performance was assessed over a range of angles of attack using a six-component force balance showing the overall performance of the membrane wing was reduced by between 5-11% depending on the analysis conducted. A stereo camera system was used to perform Digital Image Correlation (DIC) in order to quantify the full field deformation of the membrane wing structure whilst under aerodynamic load. This showed membrane deformations of up to 15% of the section thickness. The experimental membrane displacements were then used to create a deformed wing sail geometry, removing the effect of foil bend and twist, allowing a CFD investigation of the impact of membrane deformations alone. This indicated that the static membrane deformations resulted in a decrease in performance of up to 1.3% compared to the rigid aerofoil.

Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully-Activated Flapping Foil

Flapping foil energy harvesting systems are considered as highly competitive devices for conventional turbines. Several research projects have already been carried out to improve performances of such new devices. This paper is devoted to study effects of non-sinusoidal heaving trajectory, non-sinusoidal pitching trajectory, and the effective angle of attack on the energy extraction performances of a flapping foil operating at low Reynolds number (Re=1100). An elliptic function with an adjustable parameter S (flattening parameter) is used to simulate various sinusoidal and non-sinusoidal flapping trajectories. The flow around the flapping foil is simulated by solving Navier–Stokes equations using the commercial software Star CCM+ based on the finite-volume method. Overset mesh technique is used to model the flapping motion. The study is applied to the NACA0015 foil with the following kinetic parameters: a dimensionless heaving amplitude h0 = 1c, a shift angle between heaving and pitching motions = 90°, a reduced frequency f* = 0.14, and an effective angle of attack αmax varying between 15° and 50°, corresponding to a pitching amplitude in the range 0 = 55.51° to 99.51°. The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = S =1), best performances are obtained for the effective angle of attack, αmax = 40°. At small effective angle of attack αmax 40°), non-sinusoidal pitching motion has a negative effect. Performances improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching.

Numerical Analysis of the Resistance Force of Floater of Wave Glider and Flapping Motion of Single Wave Glider NACA-0012 Foil

In 2020, the Agency for the Assessment and Application of Technology – Indonesia (BPPT) is designing wave glider systems for Tsunami Early Warning System. The wave glider systems consist of two components, the floater at the water surface and the wave glider submerged 2 meters or more below the water surface. Wave glider contains several foils that can flap up and down due to the heave and pitch motion of the floater so that the system affords the force to move forward. This paper describes the numerical analysis of the resistance of floater and the selection of the pivot position of the foil where it flaps. The speed of the floater is set from 0.3 m/s up to 1 m/s. NACA-0012 is selected as the first choice of the foil. It flaps in pure pitch motion and coupled pitch and heave motion in the different pivot positions. The flapping frequency is set to 0.1 Hz since the peak period of the wave about 10 seconds. The surge forces due to the flapping motion are then analysed to determine the best position of the pivot. The numerical simulation shows that the pivot position at 2.5% - 5% of chord length from the leading edge of NACA-0012 generates the optimum surge force.

Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation.

The Effect of Mass Ratio and Damping Coefficient on the Propulsion Performance of the Semi-Active Flapping Foil of the Wave Glider

A numerical investigation on the propulsion performance of the semi-active flapping foil of the wave glider with different mass ratio and damping coefficient is investigated. The commercial CFD software Fluent is used to solve the URANS equations around the flapping foil by the Finite Volume Method. A mesh of 2D NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first analyze the effect of the mass ratio on the mean output power coefficient and propulsion efficiency and note that with the variation of the mass ratio, the propulsion efficiency decreases slightly. Besides, we find that the mass ratio has a noticeable influence on the mean output power coefficient, and the influence is determined by the reduced frequency. For high reduced frequency, with the increase of the mass ratio, the propulsion performance of the flapping foil decreases monotonously. For low reduced frequency, the mean output power increases slightly. For critically reduced frequency, the mean output power coefficient of the foil firstly increases and then decreases via the mass ratio increase. Then, we examine the influence of the damping coefficient on the propulsion performance of the flapping foil and find that the damping coefficient has a severe adverse effect on the output power and propulsion efficiency. We conclude that the influence of the damping coefficient should be considered first when we design the propulsion device of the semi-active flapping foil. Meanwhile, we should also consider the sea conditions to choose the mass ratio to optimize the flapping foil.