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The study of insect flight is important for conservation and sustainability efforts, as predicting insect dispersal can aid management programmes in tackling economic and ecological harm from, for example, invasive species. Flight mills are invaluable tools for measuring the factors of insect flight under laboratory conditions, as they lower several technical and financial barriers to conduct experiments. It is especially difficult, however, to make assumptions about the energetic cost of tethered flights conducted using different tethers, or even on different flight mills, due to the mechanical variability of the bearing friction and air resistance of the rotating assembly. This additional uncertainty necessitates a larger number of replicates for any given standard of statistical confidence. By characterising flight mill friction, this uncertainty can both be reduced in magnitude and assigned a specific, well‐defined numerical value. We present a simple methodology to characterise this friction through dynamic calibration of the flight mill, at a high statistical confidence. This study uses videography of a flight mill undergoing free velocity decay due to friction, using an in‐house developed software to extract angular velocity from video data. However, the technique is readily adaptable to other measurement techniques. Using the velocity, alongside the mass moment of inertia of the flight mill, allows us to determine the rotational friction coefficient. This friction coefficient provides precise measurements of thrust production, and therefore the energy expenditure of flight, by the tethered insect. [ABSTRACT FROM AUTHOR]

Six patents were secured by E. H. Lanier from 1930 to 1933 for aeroplane designs that were intended to be exceptionally stable. A feature of five of these was a flow-induced "vacuum chamber" which was thought to provide superior stability and increased lift compared to typical wing designs. Initially, this chamber was in the fuselage, but later designs placed it in the wing by replacing a section of the upper skin of the wing with a series of angled slats. We report upon an investigation of the Lanier wing design using inviscid aerodynamic theory and viscous numerical simulations. This took place at the 2005 Australia–New Zealand Mathematics-in-Industry Study Group. The evidence from this investigation does not support the claims but, rather, suggests that any improvement in lift and/or stability seen in the few prototypes that were built was, most probably, due to thicker airfoils than were typical at the time. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of rolling wheels at Reynolds numbers, Re D , based on wheel diameter, D , in the range of Re D ∈ 3.0 × 10 3 − 3.0 × 10 5 corresponding with translation speed of U ∞ ∈ 0.1 − 10 m/s, and varying thickness-to-diameter ratios, R = W / D ∈ 0.040,0.127,0.400 , are conducted with the objective of characterizing the coherent flow structures and their effect on forces. Previous work by A. Javadi (2022)1 for Re D = 3.0 × 10 4 shows non-monotonic variation of drag coefficients with thickness change. Under the flow conditions essayed here, C D steadily decreases as Re D increases. If R = 0.04 the drag coefficient is C D ∈ 0.4 − 1.4 , while it decreases from unity to 0.5 if R = 0.400. The lift force is downward for the wheel with R = 0.040, while it changes its direction if the thickness and/or Re D number increases. The downward lift force for rolling wheel is associated with the Magnus effect. The positive lift force, provided on the rolling wheel with R = 0.127 and 0.400, is associated with strong (positive) peak of the static pressure in the upstream vicinity of the contact point with the ground. The positive lift force also significantly decreases from unity to 0.3 as Reynolds number increases. The effects of the thickness on the flow structures in the wake are revealed, especially in high Re D numbers. On the top of the wheel, there is hairpin vortex at Re D = 3.0 × 10 3 , while the structure becomes unsteady and loses its coherence in higher Reynolds numbers. There is no coherent structures on the top of the thickest wheel because the wheel rotation avoids forming any structure. The large dipole vortex pinch off from the sides of the wheel with R = 0.400 causes large force fluctuations. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study on the power extraction of the hydrofoil by performance of the coupled oscillating heave and pitch motions. The numerical analysis is conducted by using the Reynolds Average Navier-Stokes (RANS) equations and the realizable k- ɛ turbulent model of the Star-CCM+ software. A 3D oscillating hydrofoil of NACA0015 section with aspect ratio of 7 is selected for the present analysis at two inflow velocities and three frequencies. The numerical results of lift and drag coefficients, horizontal and vertical forces coefficients, power efficiency in time domain and average value of those parameters are presented and discussed. According to the numerical results, the high efficiency of hydrofoil is found at the reduced frequency of 0.18 and the flow velocity of 1 m/s and the low efficiency is obtained at the reduction frequency of 0.06 and the flow velocity of 2 m/s. Moreover, the contour results of vorticity, streamline and pressure distribution are also presented and discussed. The computational model depicts clear vortex patterns surrounding the hydrofoil, which has a major impact on the power performance of oscillating hydrofoil.

A novel bluff-body control concept by using combined windward-and-leeward jets was introduced to modify the wake-vortex patterns and suppress the aerodynamic forces acting on a circular cylinder. Wind tunnel investigations are performed at a subcritical Reynolds number of Re = 3.33 × 104, which is a typical Re level that the wind-induced cable vibrations usually occur. The strength and effectiveness of active control in the present study are characterized with a dimensionless equivalent jet momentum coefficient Cµ. The particle image velocimetry (PIV) technique is employed to measure the wake flow patterns of the baseline and controlled cylinders to reveal the great modifications of active control to the cylinder wake. Except for PIV tests, surface pressure measurements are also conducted to obtain the pressure distribution around the cylinder surface so as to estimate the aerodynamic forces, i.e., drag and lift forces acting on the baseline and controlled cylinders. Pressure measurement results demonstrate clearly the control effectiveness and the wake flow topologies obtained by PIV system help to uncover the mechanism of windward-and-leeward jet control. [ABSTRACT FROM AUTHOR]

Leading edge surface erosion is an emerging issue in wind turbine blade reliability, causing a reduction in power performance, aerodynamic loads imbalance, increased noise emission, and, ultimately, additional maintenance costs, and, if left untreated, it leads to the compromise of the functionality of the blade. In this work, we first propose an empirical spatio-temporal stochastic model for simulating leading edge erosion, to be used in conjunction with aeroelastic simulations, and subsequently present a deep learning model to be trained on simulated data, which aims to monitor leading edge erosion by detecting and classifying the degradation severity. This could help wind farm operators to reduce maintenance costs by planning cleaning and repair activities more efficiently. The main ingredients of the model include a damage process that progresses at random times, across multiple discrete states characterized by a non-homogeneous compound Poisson process, which is used to describe the random and time-dependent degradation of the blade surface, thus implicitly affecting its aerodynamic properties. The model allows for one, or more, zones along the span of the blades to be independently affected by erosion. The proposed model accounts for uncertainties in the local airfoil aerodynamics via parameterization of the lift and drag coefficients’ curves. The proposed model was used to generate a stochastic ensemble of degrading airfoil aerodynamic polars, for use in forward aero-servo-elastic simulations, where we computed the effect of leading edge erosion degradation on the dynamic response of a wind turbine under varying turbulent input inflow conditions. The dynamic response was chosen as a defining output as this relates to the output variable that is most commonly monitored under a structural health monitoring (SHM) regime. In this context, we further proposed an approach for spatio-temporal dependent diagnostics of leading erosion, namely, a deep learning attention-based Transformer, which we modified for classification tasks on slow degradation processes with long sequence multivariate time-series as inputs. We performed multiple sets of numerical experiments, aiming to evaluate the Transformer for diagnostics and assess its limitations. The results revealed Transformers as a potent method for diagnosis of such degradation processes. The attention-based mechanism allows the network to focus on different features at different time intervals for better prediction accuracy, especially for long time-series sequences representing a slow degradation process.

The flow on the upper surface of NACA 0015 airfoil is subject to an adverse pressure gradient when the incidence increases. This leads to the boundary layer separation which causes losses in the aerodynamic performances. Control using Vortex Generators (VGs) is a simple passive mean used to delay or eliminate the flow separation from the wall. The two main objectives of the experimental work performed consist in the optimization by experimental design method "DoE" of a new VGs configuration, inspired by Lin's one, by varying its different geometrical parameters. A comparative efficiency study of the two VGs configurations (Lin's VGs, modified VGs) on aerodynamic performances was then undertaken at different Reynolds numbers. In addition to the significant improvement in lift around 22%, the study resulted in a drag reduction of approximately 16% and a stall delay of two degrees. The results were also compared to a three-dimensional numerical simulation (3D-RANS) and showed good agreement. The CFD results highlighted a clear improvement in the momentum thickness along the airfoil's upper face, particularly a rate of 44.44% at 40% of the chord length. [ABSTRACT FROM AUTHOR]

Cavitation characteristics and hydrodynamic forces of hydrofoils with bioinspired, wavy leading edges were examined experimentally in a water tunnel. Force measurements were carried out using a waterproof load cell, and cavitation patterns were recorded by directly imaging the hydrofoil surface. All semi-span hydrofoils had an underlying NACA 63 4 -021 profile with either a rectangular or swept leading edge planform. The sinusoidal leading edge geometries were defined by three amplitudes of 2.5%, 5%, and 12% and two wavelengths of 25% and 50% of the mean chord length. Results revealed that cavitation on the modified hydrofoils with the two larger amplitudes was largely confined to the regions directly behind the protuberance troughs, whereas a baseline with flat leading edge and the smaller amplitude hydrofoils exhibited sheet cavitation over the entire span. Additionally, cavitation on the modified hydrofoils appeared at consistently lower angles of attack than on the baseline model. Lift coefficient for the baseline model was generally comparable to or greater than that of the modified hydrofoils at the angles of attack considered. Except for the largest amplitude hydrofoils, drag for the modified hydrofoils was equal to the baseline model for nearly the entire angle of attack range. [ABSTRACT FROM AUTHOR]

Purpose: This study focuses on one of the key design aspects of mine ventilation fans, i.e. the selection of an appropriate aerofoil blade profile for the fan blades in order to enhance the energy efficiency of axial flow mine ventilation fans, using CFD simulations. Methods: Computational simulations were performed on six selected typical aerofoil sections using CFD code ANSYS Fluent 6.3.26 at angles of attack varying from 0° to 21° at an interval of 3° and at Reynolds number Re=3×106 , and various aerodynamic parameters, viz. coefficients of lift (Cl) and drag (Cd) as a function of angle of attack (α) were determined to assess the efficiency of the aerofoils. Results: The study revealed that the angle of attack has a significant effect on the lift and drag coefficients and stall condition occurred at α values of 12° and 15° in most of the aerofoils. Based on the criterion of higher lift to drag ratio (Cl/Cd), a blade profile was chosen as the most efficient one for mine ventilation fans. Practical implications: This study forms a basis for selecting appropriate blade profiles for the axial flow fans used for ventilation in mining industry. Originality/value: The application of an appropriate aerofoil blade profile will impart energy efficiency to the mine ventilation fans and thereby result in energy saving in mine ventilation.

The following considers lift and drag measurements of 13 production golf ball models propelled through still air in a laboratory setting. The balls travelled at speeds ranging from 18 m/s to 91 m/s and spin ranging from 1500 rpm to 4500 rpm. Speed sensors measured the speed and location of the balls at three locations from which the coefficient of lift and drag were found. The sensors were sufficiently close (3.81 m to 5.08 m) so that the lift and drag effects were nearly constant. Lift and drag were observed to depend on speed, spin rate, and ball model. The difference in the drag coefficient between the ball models were relatively large (>0.1) at low speed (Re < 105), and smaller ( 105). The lift coefficient had a non-linear dependence on spin (fit with a 2nd order polynomial). A trajectory of each ball model was found from the measured lift and drag response. Carry distance varied by 18 m over the models considered here and was not strongly correlated with ball cost.

Purpose – The purpose of this paper is to present a method to conduct small satellite rendezvous mission by using the differential aerodynamic forces under J2 perturbation in low earth orbit (LEO). Design/methodology/approach – Each spacecraft is assumed to be equipped with two large flat plates, which can be controlled for generating differential accelerations in all three directions. Based on the kinetic theory, the aerodynamic lift and drag generated by a flat plate are calculated. To describe the relative dynamics under J2 perturbation, a modified model is derived from the high-fidelity linearized J2 equations proposed by Schweighart and Sedwick. Findings – Simulation results demonstrate that the proposed method is valid and efficient to solve satellite rendezvous problem, and the modified model considering J2 effect shows better accuracy than the Horsley’s Clohessy–Wiltshire-based model. Research limitations/implications – Because aerodynamic force will reduce drastically as orbital altitude rises, the rendezvous control strategy for small satellites presented in this paper should be limited to the scenarios when satellites are in LEO. Practical implications – The rendezvous control method in this paper can be applied to solve satellite rendezvous maneuver problem for small satellites in LEO. Originality/value – This paper proposes a modified differential aerodynamic control model by considering J2 perturbation, and simulation results show that it can achieve higher rendezvous control accuracy. [ABSTRACT FROM AUTHOR]

The two-dimensional flow around a rotating cylinder is investigated numerically using a vorticity forces formulation with the aim of analyzing quantitatively the flow structures, and their evolutions, that contribute to the lift and drag forces on the cylinder. The Reynolds number considered, based on the cylinder diameter and steady free stream speed, is Re=200, while the non-dimensional rotation rate (ratio of the surface speed and free stream speed) selected was α =1 and 3. For α =1 the wake behind the cylinder for the fully developed flow is oscillatory due to vortex shedding, and so are the lift and drag forces. For α =3 the fully developed flow is steady with constant (high) lift and (low) drag. Each of these cases is considered in two different transient problems, one with angular acceleration of the cylinder and constant speed, and the other one with translating acceleration of the cylinder and constant rotation. We characterize quantitatively the contributions of individual fluid elements (vortices) to aerodynamic forces, explaining and quantifying the mechanisms by which the lift is generated in each case. In particular, for high rotation (when α =3), we explain the relation between the mechanisms of vortex shedding suppression and those by which the lift is enhanced and the drag is almost suppressed when the fully developed flow is reached. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a numerical study of incompressible, steady, three-dimensional turbulent air flow inside and around a simplified air-cushion vehicle (ACV) model. Two distinct cases have been studied separately regarding type of motion of the ACV; the first case is sole hovering with no forward motion where only flow through the ACV was considered, the second case is both hovering and translational motions for which the external flow around the vehicle body becomes of interest. It is assumed that both motions take place on land (above a solid plane). A hybrid mesh was generated and solutions were obtained for various lift fan pressures and air-clearance heights. Computations have been carried out by means of the computational fluid dynamics (CFD) software ANSYS FLUENT. Mean flow aerodynamic characteristics of the ACV are presented and discussed in terms of lift and drag forces, factors contributing to the drag, flow separations and singular points in the streamline patterns. The Q-criterion is employed to identify vortical structures. Differences in the aerodynamic characteristics of an ACV and a road vehicle are also discussed. [Copyright &y& Elsevier]

This paper presents the development of flexible wings, flapping mechanism, and integrated electronic control system (ECS) to emulate the bat wing flapping for the ongoing micro air vehicle (MAV) research. Three bat species having dimensions close to the design requirement of MAV, namely, Mormopterus Planiceps, Nytophilus Geoffroyi, and Scotorepens Balstoni were selected, and the average of their physical dimensions was chosen. The commercially available titanium alloy, Ti ± 6Al ± 4V, was used for the wing frame, and the membrane was made of latex. A four-bar slider-crank mechanism was designed and fabricated to facilitate the wing flapping; ECS controlled the flapping frequency in the real-time mode. The system was tested in open air wind tunnel at frequency 6 Hz, angle of attack (AOA) 0-50°, and velocity range 2-7 m s−1. The experimental flapping angle which is compared with the theoretical flapping angle was obtained from the analytical kinematic model. The mean lift and drag coefficients were also measured and the results were found to be excellent. Compared to the manual control and measurement of flapping frequency, the proposed ECS demonstrates efficient control and accurate measurement. Moreover, the tedious procedure involved in the repeated calibrations for the manual system is totally eliminated by ECS. [ABSTRACT FROM AUTHOR]

Abstract: The present study experimentally investigates the hydrodynamic behaviour of 2-D NACA (15%, 25% and 35%) symmetric hydrofoils at Reynolds number 0.5×106. Particular attention was paid to the hysteretic behaviour at the static stall angle, and a detailed cartography of the boundary layer structures (integral quantities and velocity profiles) is given to support the detachment mechanism and the onset of von Kármán instability for thick hydrofoils. [Copyright &y& Elsevier]

Abstract: A transversely oscillating cylinder in a uniform flow is modeled to investigate frequency effects of flow-induced wake on lift and drag of the cylinder. Specifically, verified unsteady fluid dynamic simulations using an immersed-boundary method in a fixed Cartesian grid predict the flow structure around the cylinder and reveal how the integration of surface pressure and shear distributions provides lift and drag on the oscillating cylinder. In this study, frequency ranges to be considered are both near and away from the natural frequency of wake vortex shedding. Subsequently, the effects of frequency lock-in, superposition and demultiplication on lift and drag are discussed based on the spectral analysis of time histories of lift and drag. [Copyright &y& Elsevier]

Leading edge surface erosion is an emerging issue in wind turbine blade reliability, causing a reduction in power performance, aerodynamic loads imbalance, increased noise emission, and, ultimately, additional maintenance costs, and, if left untreated, it leads to the compromise of the functionality of the blade. In this work, we first propose an empirical spatio-temporal stochastic model for simulating leading edge erosion, to be used in conjunction with aeroelastic simulations, and subsequently present a deep learning model to be trained on simulated data, which aims to monitor leading edge erosion by detecting and classifying the degradation severity. This could help wind farm operators to reduce maintenance costs by planning cleaning and repair activities more efficiently. The main ingredients of the model include a damage process that progresses at random times, across multiple discrete states characterized by a non-homogeneous compound Poisson process, which is used to describe the random and time-dependent degradation of the blade surface, thus implicitly affecting its aerodynamic properties. The model allows for one, or more, zones along the span of the blades to be independently affected by erosion. The proposed model accounts for uncertainties in the local airfoil aerodynamics via parameterization of the lift and drag coefficients' curves. The proposed model was used to generate a stochastic ensemble of degrading airfoil aerodynamic polars, for use in forward aero-servo-elastic simulations, where we computed the effect of leading edge erosion degradation on the dynamic response of a wind turbine under varying turbulent input inflow conditions. The dynamic response was chosen as a defining output as this relates to the output variable that is most commonly monitored under a structural health monitoring (SHM) regime. In this context, we further proposed an approach for spatio-temporal dependent diagnostics of leading erosion, namely, a deep learning attention-based Transformer, which we modified for classification tasks on slow degradation processes with long sequence multivariate time-series as inputs. We performed multiple sets of numerical experiments, aiming to evaluate the Transformer for diagnostics and assess its limitations. The results revealed Transformers as a potent method for diagnosis of such degradation processes. The attention-based mechanism allows the network to focus on different features at different time intervals for better prediction accuracy, especially for long time-series sequences representing a slow degradation process. [ABSTRACT FROM AUTHOR]

The greatly-stretched lateral opening of penaeid trawls is typically achieved by using relatively large otter boards with an aspect ratio of ~ 0.5 at high angle of attack (AOA; ~ 40°) and low efficiency (lift-to-drag ratio; L/D ~ 1). Alternatively, the 'batwing' otter board utilises a unique rigging system to allow a flexible sail with an aspect ratio of ~1 to operate at a lower AOA (~ 20°). As a result, high effectiveness (lift) and efficiency (L/D ~3) are achieved for small- and medium-size gear. However, for large trawlers it is impractical to simply scale up the current batwing design as this will excessively increase the trawl's height and generate unnecessary drag. Hence, here we experimentally searched for greater hydrodynamic forces from a multi-sail configuration (comprising a jib and main sail) by varying the twist and camber of the two sails. The results suggest that the jib needs to be set at a low AOA compared to the main sail for balanced pressure loading of the two sails, and the main sail requires medium twist to control detrimental centre of pressure characteristics. Ultimately the desired objective for large-sized batwing boards might best be achieved using a two-mast configuration that incorporates three sails. • It is impractical to use single-sail batwing boards on large prawn trawlers. • A multi-sail batwing configuration was tested to seek large hydrodynamic forces. • Generally the multi-sail was not superior to single-sail designs. • Better performance is likely if balanced loading of the jib and main-sail is achieved. [ABSTRACT FROM AUTHOR]