Aerodynamic Advantages Research Articles

Modeling and Testing of a Seamless Wing Trailing Edge Control Actuation System

This paper presents an investigation into the modeling and analysis of an innovative actuation system for a wing with a seamless flexible trailing edge control surface. Research was started with the study of aerodynamic behavior and advantage of the wing in smooth variable chamber shape under control. Based on the concept and design, an experimental wing section integrated with the actuation mechanism was built and tested. The main effort was then made to the modeling of the internal actuation system for the purpose of obtaining the physical properties and accurate modeling of the whole wing structural system. To validate and update the numerical model of the system, vibration test of the actuation system including the mechanism and actuator was carried out. Some key parameters such as the stiffness of the actuation system were identified from vibration test data. The investigation demonstrated a practical approach to quantify some key parameters and update the numerical model of an actuation system.

Aerodynamic Improvements of Wind-Turbine Airfoil Geometries With the Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method

The prescribed surface curvature distribution blade design (CIRCLE) method can be used for the design of two-dimensional (2D) and three-dimensional (3D) turbomachinery blade rows with continuous curvature and slope of curvature from leading edge (LE) stagnation point to trailing edge (TE) stagnation point and back to the LE stagnation point. This feature results in smooth surface pressure distribution airfoils with inherently good aerodynamic performance. In this paper the CIRCLE blade design method is modified for the design of 2D isolated airfoils. As an illustration of the capabilities of the method, it is applied to the redesign of two representative airfoils used in wind turbine blades: the Eppler 387 airfoil and the NREL S814 airfoil. Computational fluid dynamic analysis is used to investigate the design point and off-design performance of the original and modified airfoils, and compare with experiments on the original ones. The computed aerodynamic advantages of the modified airfoils are discussed. The surface pressure distributions, drag coefficients, and lift-to-drag coefficients of the original and redesigned airfoils are examined. It is concluded that the method can be used for the design of wind turbine blade geometries of superior aerodynamic performance.

Optimization of Flatback Airfoils for Wind-Turbine Blades Using a Genetic Algorithm

In recent years, the airfoil sections with blunt trailing edges (called flatback airfoils) have been proposed for the inboard regions of largewind-turbine blades because they provide several structural and aerodynamic performance advantages. In this paper, a genetic algorithm is used for shape optimization of flatback airfoils for generating maximum lift-to-drag ratio. The computational efficiency of a genetic algorithm can be significantly enhanced with an artificial neural network. The commercially available software FLUENT is used for calculation of the flowfield using the Reynolds-averaged Navier–Stokes equations in conjunction with a turbulence model. It is shown that the genetic algorithm optimization technique is capable of accurately and efficiently finding globally optimal flatback airfoils.

The compression effect on aerodynamic properties of sports fabrics

Generally, the surface textures of the sport fabrics influence the aerodynamic properties of the athletes in motion. On the other hand, the surface texture of sports garments largely depends on the applied stress while wearing. Therefore, the fitting of garments on athlete bodies can make the aerodynamic behaviour more complex. Additionally, the fabric at an appropriate level of stretching can provide an aerodynamic advantage. The primary objective of this study was to measure the aerodynamic properties of three commercially available sport fabrics using a standard cylinder methodology over a range of Reynolds numbers and stretch conditions alone with microscopic analysis. The results indicated that the surface texture of the fabric was changed under different stretched levels and these changes in the surface texture had a notable effect on the aerodynamic drag. The surface texture of fabrics caused transitional effect at lower speeds compared to the smooth bare cylinder providing almost 30% drag reduction.

Aerodynamics of ski jumping suits

The primary purpose of this study is to understand the aerodynamic behaviour of textile fabrics used in ski jumping suits. Macro-scale (cylinder) and full-scale aerodynamic investigations of ski jumping suits and fabrics were undertaken. The aerodynamic effects of surface morphology of ski jumping fabrics were measured. On the basis of the macro-scale investigation, two full-scale ski jumping suits were developed and tested. The results from the macro-scale investigation show that the surface morphology affects the aerodynamic parameters (drag, lift and lift-to-drag ratio). The modified suit based on cylindrical test data shows 2.2% gain in lift-to-drag ratio, which can result in a difference in jump length of up to 4.44 m. The results also indicate that these effects can be utilised in ski jumping suit development to gain aerodynamic advantages. The analysed data from the full-scale investigation confirms the gain obtained from the macro-scale testing.

Aerodynamic behaviour of stretchable sports fabrics

The variable surface characteristics of sports fabrics can affect the aerodynamics of athletes. In speed sports, most sports garments are worn with reasonable stretches that alter the fabrics' surface morphology. However, no correlation between the stretches and aerodynamic parameters is reported in the open literature. Therefore, the primary objective of this paper is to measure the aerodynamic properties of three commercially available sports fabrics over a range of Reynolds numbers and stretch conditions. Aerodynamic parameters of each fabric under a range of applied stretches were measured experimentally. The findings indicate that the surface morphology of the fabric under tension changes significantly and also affects the aerodynamic behaviour of the fabric. Less stretched knitted fabrics can provide an aerodynamic advantage by reducing drag at higher speeds, while more stretched knitted fabrics can provide an aerodynamic advantage by reducing drag at lower speeds. As the surface roughness increases, the critical Reynolds number (Recrit ) decreases and the minimum drag coefficient (C Dmin) value increases. Using same fabric under different tensions, the aerodynamic drag can be reduced up to 40% compared to a smooth-surface fabric.

Flying in a flock comes at a cost in pigeons

Flying birds often form flocks, with social1, navigational2 and anti-predator3 implications. Further, flying in a flock can result in aerodynamic benefits, thus reducing power requirements4, as demonstrated by a reduction in heart rate and wingbeat frequency in pelicans flying in a V-formation5. But how general is an aerodynamic power reduction due to group-flight? V-formation flocks are limited to moderately steady flight in relatively large birds, and may represent a special case. What are the aerodynamic consequences of flying in the more usual ‘cluster’ 6,7 flock? Here, we use data from innovative back-mounted GPS and 6 degree of freedom inertial sensors to show that pigeons 1) maintain powered, banked turns like aircraft, imposing dorsal accelerations of up to 2g, effectively doubling body weight and quadrupling induced power requirements; 2) increase flap frequency with increases in all conventional aerodynamic power requirements; and 3) increase flap frequency when flying near, particularly behind, other birds. Therefore, unlike V-formation pelicans, pigeons do not gain an aerodynamic advantage from flying in a flock; indeed, the increased flap frequency – whether due to direct aerodynamic interactions or requirements for increased stability or control – suggests a considerable energetic cost to flight in a tight cluster flock.

Comparative aerodynamic analysis of commercial swimsuits

The primary objective of this research is to investigate and describe the effects of swimsuits' surface profile and seam orientations on aerodynamic drag. Two commercial swimsuits (Speedo LZR and TYR Sayonara) materials were evaluated in a wind tunnel environment using a standard cylindrical experimental arrangement. The effects of swimsuit surface profile and seam orientations on aerodynamic drag were evaluated for a range of Reynolds numbers. The measured drag forces were converted to dimensionless drag coefficients, which were compared for both swimsuits under different conditions. The results show that the material surface structure (roughness and seam orientations) of the swimsuit has significant effect on aerodynamic drag. The seam orientation at 45° has the potential to reduce the drag by around 15% depending on the seam geometry (i.e., seam height, width, etc.) and Reynolds number. The TYR Sayonara swimsuit can provide aerodynamic advantage at low Reynolds number (e.g. below Re = 1.63 × 105) due t...

Clouding the Issue

Biophysics As anyone who has played table tennis knows, it's hard to throw a table tennis ball very far. Fungal spores, being even smaller and lighter, suffer much more from drag when they are ejected into air; individual Sclerotinia sclerotiorum spores are roughly 10 µm in size and would be predicted to travel only 3 mm after having been launched at a speed of almost 10 m s−1. Streamlining the shape of the spore and sticking to one's brethren do confer some aerodynamic advantages and lead to wider dispersal. Roper et al. show that emerging in a cloud helps, too, and can boost the distance traveled to as much as 10 cm. This enhancement arises from the earliest spores having set the proximal layer of air into motion so that later spores can go with the flow. The authors numerically simulate the spatiotemporal behavior of the spore jet and find a good match with particle-imaging velocimetry measurements. They also find that spores that wait to emerge, so as to board the already moving air mass, can delay their departure only by around 50 ms lest the train leave the station without them. Proc. Natl. Acad. Sci. U.S.A. 107 , 10.1073/pnas.1003577107 (2010).

Numerical Investigation on Aerodynamic Performance for Guiding VAWT with Combined Blades

In this paper, the reason was analyzed that the aerodynamic efficiency of the traditional vertical axis wind turbine (VAWT) was always low, and a new type of VAWT—Guiding VAWT was introduced. On that basis, a new blade shape called as combined blade for Guiding VAWT was proposed and numerical investigation was complemented on its aerodynamic performance by CFD (Computational Fluid Dynamics) technique. This Guiding VAWT includes two components: guiding impeller and rotating impeller, which are both combined blade in shape. The guiding blade is combined by three sections: inlet radial section, middle arc section and outlet linear section. The wind blade is combined by two sections, inlet arc section and outlet linear section. The combined guiding blade may not only avoid the wind impeller from the direct impact by the coming flow on its convex surface of the blade so as to decrease the drag torque but also improve the effective impact by the coming flow on the concave surface of the blade, both of which contribute the enhancement for the driving torque of the wind turbine. Results indicate: This new type of Guiding VAWT with combined blade has a wider operating range, higher aerodynamic efficiency than the traditional VAWTs. And more, this paper introduced the airfoil blade into this new type of VAWT and numerically validated that even though the flow inside VAWT was a large separated flow with variable attack angles, the aerodynamic advantage of the airfoil blade could still be shown to some extent, which hoped to further enhance the aerodynamic efficiency of the VAWT. Additionally, this new type of VAWT has a two dimensional structure for convenient manufacture, which has the latent energy to be popularized.

An experimental study of a bio-inspired corrugated airfoil for micro air vehicle applications

An experimental study was conducted to investigate the aerodynamic characteristics of a bio-inspired corrugated airfoil compared with a smooth-surfaced airfoil and a flat plate at the chord Reynolds number of ReC = 58,000–125,000 to explore the potential applications of such bio-inspired corrugated airfoils for micro air vehicle designs. In addition to measuring the aerodynamic lift and drag forces acting on the tested airfoils, a digital particle image velocimetry system was used to conduct detailed flowfield measurements to quantify the transient behavior of vortex and turbulent flow structures around the airfoils. The measurement result revealed clearly that the corrugated airfoil has better performance over the smooth-surfaced airfoil and the flat plate in providing higher lift and preventing large-scale flow separation and airfoil stall at low Reynolds numbers (ReC < 100,000). While aerodynamic performance of the smooth-surfaced airfoil and the flat plate would vary considerably with the changing of the chord Reynolds numbers, the aerodynamic performance of the corrugated airfoil was found to be almost insensitive to the Reynolds numbers. The detailed flow field measurements were correlated with the aerodynamic force measurement data to elucidate underlying physics to improve our understanding about how and why the corrugation feature found in dragonfly wings holds aerodynamic advantages for low Reynolds number flight applications.

Aerodynamic Characteristics of Forward and Aft Swept Arrow Wings

D ESPITE aerodynamic advantages, aeroelastic complications have precluded the wide-scale adoption of the forward swept wing planform [1]. Forward swept wings may demonstrate liftdependent drag benefits due to spanwise load distributions that are closer to elliptic then an equivalent aft swept wing [2]. Fuselageinduced spanwise flow is also beneficial for forward swept wings; it reduces the effective sweep, whereas the opposite is true for aft swept wings [3]. The most apparent benefit of the forward sweep configuration is in lateral control; spanwise flow toward the root delays flow separation over the ailerons, whereas the opposite is true for aft swept wings [4]. Little information is available on the effect of highly swept wingswith forward sweepwhere flow separation is enforced. Consequently, an investigation has been undertaken using a 65 deg sweep arrow wing with fore and aft extensions.

Drag Characteristics for Optimally Span-Loaded Planar, Wingletted, and C Wings

This paper focuses on the drag characteristics of optimally span-loaded planar, wingletted, and C wings. The span load is optimized resulting in minimum induced or total drag. The wing-root bending moment is kept constant for all analyzed wings to ascertain that different wings have comparable weight. The optimum span loadings for the different types of wing are calculated using a fast and simple numerical method. The wings are analyzed in the Trefftz plane, infinitely far behind the wing. Lagrange multipliers are used to calculate the optimum span loading resulting in minimum induced or total drag, with the wing-root bending moment and/or the lift coefficient as constraint. The induced drag can be calculated using the optimum span loading. The profile drag is assumed to be a function of the local lift coefficient. The results indicate that the C wing does not have real aerodynamic performance advantages compared to a wingletted wing. For wings with span and/or aspect ratio constraints, a winglet offers a drag reduction relative to a planar wing.

Aerodynamics Simulation of Hypersonic Waverider Vehicle

The purpose of this paper is to examine the aerodynamic characteristics of three hypersonic configurations. Three hypersonic forebodies were designed. For the purpose to integrate with ramjet or scramjet, all forebodies were designed integrated with hypersonic inlet.To better understand the forebody performance, three dimensional flow field calculations of these hypersonic forebodies integrated with hypersonic inlet were conducted in the design and off design conditions. Computational result show that waverider offer an aerodynamic performance advantage in the terms of high lift-drag ratios over the other two configurations. Liftbody offer good aerodynamic performance in subsonic region. The aerodynamic performance of the liftbody integrated with waverider configuration is not comparable to that of pure waverider in the terms of lift-drag ratios and is not comparable to that of pure liftbody in subsonic. But the liftbody integrated with waverider configuration exhibit good lateral-directional and longitudinal-directional stability characteristics. Both pure waverider and liftbody integrated with waverider configuration can provide relatively uniform flow for the inlet and offer good aerodynamic characteristics in the terms of recovery coefficient of total pressure and uniformity coefficient.

Experimental investigation of wing-in-ground effect with a NACA6409 section

The aerodynamic characteristics of NACA6409 in the vicinity of the ground were experimentally studied in a wind tunnel. Lift and drag forces, the pitching moment, and the center of pressure were measured with respect to various major aerodynamic parameters, such as the ground clearance, the angle of attack, the aspect ratio (AR), and the endplate type, which resulted in a total number of 420 conditions. In addition, a smoke trace test was conducted to visualize the flow pattern around NACA6409 in the vicinity of the ground. As a result of the ground effect and the influence of the endplate, the lift-to-drag ratio increased at low ground clearance and the center of pressure moved forward to the leading edge; that is, the endplate and ground effects were equivalent to the aerodynamic advantage that results from increasing the AR of the wing. Extended experimental results are useful for understanding the aerodynamic characteristics influenced by each aerodynamic parameter during ground effect as well as for verifying numerical simulation.

Aerodynamics of a Flapping and Pitching Wing Using Simulations and Experiments

Computational fluid dynamics simulation results for a thin cambered plate airfoil, and flow visualization and force measurements from experiments conducted in water on a flapping-and-pitching thin flat-plate wing of semi-elliptic planform at low Reynolds numbers are reported. Time-varying force data, measured using a force transducer, provide a means to understand the mechanisms that lead to enhanced performance observed in insect flight compared with fixed-wing aerodynamics. Experimental uncertainties associated with low-level (∼1 N) fluid dynamic force measurements on flapping-and-pitching wings, including inertia effects, are addressed. A previously proposed pitching mode in which the leading-edge and trailing-edge switch roles to allow using cambered airfoils is shown to be feasible. A vortex-trapping model is proposed to explain the aerodynamic advantages of switching. The present results also support the authors' proposed idea that an optimum reduced flapping frequency might exist. The study has applications in micro air vehicle development.

Modeling and Autopilot Design of Blended Wing-Body UAV

This paper describes the modeling and autopilot design procedure of a Blended Wing-Body(BWB) UAV. The BWB UAV is a tailless design that integrates the wing and the fuselage. This configuration shows some aerodynamic advantages of lower wetted area to volume ratio and lower interference drag as compared to conventional type UAV. Also, BWB UAV may be increase payload capacity and flight range. However, despite of these benefits, this type of UAV presents several problems related to flying qualities, stability, and control. In this paper, the detailed modeling procedure of BWB UAV and stability analysis results using the linearized model at trim condition are represented. Finally, we designed the autopilot of BWB UAV based on a simple control allocation scheme and evaluated its performance through nonlinear simulation.

Analysis of the structure of mathematical models of unsteady aerodynamic coefficients

Approaches as the base for obtaining mathematic models of aerodynamic coefficients are considered. Two most complete models of unsteady aerodynamic coefficients comparable analysis is doing. Unsteady integral model of aerodynamic coefficients advantage is demonstrated.

Aerodynamic advantages of upside down take-off for aerial dispersal in Tetranychus spider mites

Aerial dispersal may be important for redistribution of spider mites into new habitats. Evidence for behavioral control of aerial take-off has been well documented for Tetranychus urticae Koch. Before aerial dispersal they exhibit the aerial take-off posture that involves lifting the forelegs upright and raising the forebody. However, whether the aerial take-off posture functions to increase drag has remained unclear. The objectives of this study were to clarify: (i) aerodynamic effects of the aerial take-off posture; and (ii) actual aerial take-off behavior in T. urticae. To evaluate the aerodynamic forces experienced by grounded spider mites in different postures, we constructed three-dimensional models of T. urticae, exhibiting the aerial take-off posture and the normal posture, using computer graphics. We found that the aerial take-off posture was effective in receiving greater rearward forces from wind rather than upward forces. As a result, aerial take-off from a horizontal platform is unlikely. Instead, inverted departure surfaces, e.g., lower leaf surfaces, with inclines are likely to be effective sites for take-off. Laboratory experiments and field observations indicated that the mites preferentially adopted such a position for orientation and take-off. Our findings provided a rationale for the take-off behavior of Tetranychus spider mites.

A new bionic MAV’s flapping motion based on fruit fly hovering at low Reynolds number

On the basis of the studies on the high unsteady aerodynamic mechanisms of the fruit fly hovering the aerodynamic advantages and disadvantages of the fruit fly flapping motion were analyzed. A new bionic flapping motion was proposed to weaken the disadvantages and maintain the advantages, it may be used in the designing and manufacturing of the micro air vehicles (MAV’s). The translation of the new bionic flapping motion is the same as that of fruit fly flapping motion. However, the rotation of the new bionic flapping motion is different. It is not a pitching-up rotation as the fruit fly flapping motion, but a pitching-down rotation at the beginning and the end of a stroke. The numerical method of 3rd-order Roe scheme developed by Rogers was used to study these questions. The correctness of the numerical method and the computational program was justified by comparing the present CFD results of the fruit fly flapping motion in three modes, i.e., the advanced mode, the symmetrical mode and the delayed mode, with Dickinson’s experimental results. They agreed with each other very well. Subsequently, the aerodynamic characteristics of the new bionic flapping motion in three modes were also numerically simulated, and were compared with those of the fruit fly flapping. The conclusions could be drawn that the high unsteady lift mechanism of the fruit fly hovering is also effectively utilized by this new bionic flapping. Compared with the fruit fly flapping, the unsteady drag of the new flapping decreases very much and the ratio of lift to drag increases greatly. And the great discrepancies among the mean lifts of three flapping modes of the fruit fly hovering are effectively smoothed in the new flapping. On the other hand, this new bionic flapping motion should be realized more easily. Finally, it must be pointed out that the above conclusions were just drawn for the hovering flapping motion. And the aerodynamic characteristics of the new bionic flapping motion in forward flight are going to be studied in the next step.