Rectangular Wing Research Articles

Aero-Propulsive Interactions between UAV Wing and Distributed Propellers Due to Their Relative Position

The purpose of this paper is the evaluation of the aero-propulsive effects on a UAV wing model with distributed propulsion. An array of three propellers is placed ahead of the leading edge of a rectangular wing with flap. The investigation was performed with high-fidelity numerical analyses to provide insights into the phenomenology and to screen the interesting positions to be validated in the wind tunnel. The propellers’ array is moved into twelve different positions, allowing longitudinal and vertical translations. The wing has an untwisted and constant section profile, with a single slot trailing-edge flap that is deflected into three positions. The flap span is entirely covered by the propellers’ blowing. Results show an increment of lift, drag, and pitching moment coefficients with distributed propellers enabled. For a given thrust level, the magnitude of such increments depends on the propellers’ positions, the flap configuration, and the angle of attack. The lift enhancement sought in distributed propulsion applications comes at the expense of a significant increase in drag and pitching moment magnitude. In some combinations, the wing’s contribution to the aircraft longitudinal stability is severely affected. Conversely, the propellers’ inflow is altered such that thrust is increased in all the investigated configurations, with a small reduction of propulsive efficiency.

Asymptotic Theory of Flapping Wing Propulsion in Extreme Ground Effect

This study, dedicated to flapping wing propulsion in immediate proximity to a wall or between closely spaced flat walls, makes use of the method of matched asymptotic expansions. Its purpose is to create a simplified parametric model of such a propulsion system based on a single major assumption: immediate closeness of oscillating wing to a solid wall. In the case of a rectangular finite-aspect ratio wing, analytical expressions have been obtained for the coefficients of instantaneous and period-averaged thrust force as well as for the efficiency of the propulsor as a function of distance from the wall, Strouhal number and wing aspect ratio for selected cases of heaving, pitching and combined oscillations. It is shown that for some oscillation modes closeness to the ground results in increases in thrust and efficiency, and that optimally combined (considering ratio of the amplitudes and phase shift of contributing motions) heave–pitch oscillations allow to maximize thrust or efficiency of the flapping-wing propulsor. Increase in aspect ratio and decrease in Strouhal number (relative frequency of oscillations) in the case of heaving invariably brings about the increase in the ideal efficiency. An example is provided of a non-planar extreme ground effect application considering oscillations of a ring-wing embracing circular cylinder. A rule is derived for recalculation of the characteristics of the flapping-wing propulsor near a flat wall onto the characteristics of the same wing operating in a narrow canal between parallel walls. This rule can also be applied to evaluate propulsive properties of a ring-wing oscillating between co-axial cylindric surfaces.

Application of wavy leading edge to enhance winglet aerodynamic performance

AbstractThe wavy leading edge (WLE, also known as leading edge protuberances) is a passive flow control device inspired by the humpback whale pectoral flippers. It reduces the flow of three-dimensional effects on wings and increases their aerodynamic performance at high angles of attack. Despite the numerous studies on its aerodynamic benefits, research on its possible applications is still incipient. Therefore, this article addresses an evaluation of the WLE effects on the aerodynamic performance of a winglet. A rectangular wing, a base smooth leading edge winglet, and a winglet with WLE were designed and manufactured for CFD simulations and wind tunnel measurements. The winglet with WLE increased the maximum aerodynamic efficiency, i.e. this configuration reduced the induced drag by increasing wingtip vortex dissipation at a given angle-of-attack. Such results were used in re-evaluations of the aerodynamic performance of an original agricultural aircraft initially configured with a multi-winglet device. The winglet with WLE showed to be effective at increasing the aircraft operational time and range under a simulated actual condition.

Wing rock mode and its mechanism of a flying-wing aircraft

The flying wing is an aerodynamic configuration with high efficiency, but the lack of lateral-directional stability has always been an obstacle that limits its application. In this study, the wing rock motion of a 65° swept flying-wing aircraft is studied via wind tunnel experiments and numerical simulations at a low speed, and various unsteady motion phenomena are focused on. Both the experimental and numerical results show that the flying wing has a bicyclic ${C_l}$ – $\phi $ hysteresis loop during its wing rock, different from the slender delta wing, rectangular wing, generic aircraft configuration, etc., which have a tricyclic hysteresis loop. This form of hysteresis loop implies a different energy exchange manner of the flying wing in the wing rock oscillation. Further analysis shows that the flying wing forms a unilateral leading-edge vortex (LEV) under a high roll angle, with its wing rock oscillation driven by the ‘vortex–shear-layer’ structure, which is different from that of slender and non-slender delta wings. Moreover, the quantitative dynamic hysteresis characteristics of the LEV's strength and location for the flying wing and the slender delta wing are also different. These results have proven the existence of a wing rock mode which is different from previous investigations, which enriches the understanding of self-induced oscillation. Present discoveries are also conducive to the aerodynamic shape design and flight manipulation of a flying-wing aircraft, which is significant for its wider application.

Effect of Leading-Edge Gap Size on Multiple-Element Wing NACA 43018

Generally, large airplanes are added with more than one high lift device to improve aerodynamic performance. Each configuration of the addition of high lift devices will result in different aerodynamic performances. The added high-lift devices include flaps, leading-edge slats, vortex generators, fences, and others. This study shows the aerodynamic performances of the NACA 43018 wing airfoil with the addition of leading-edge slats and plain flaps in cruise conditions with variations of leading-edge gap size. The angles of attack used include 0°, 2°, 4°, 6°, 8°, 10°, 12°, 15°, 16°, 17°, 19°, and 20°. Numerical simulations have been performed using Ansys Fluent 19.1 with a k-ε Realizable turbulent model. The aerodynamic performance of the configuration that uses the leading-edge slat shows a higher value than the rectangular wing even though the lift and drag coefficients produce lower values. The use of leading-edge slats produces fluctuations, which are indicated by different values of the pressure coefficient, that show the interaction of adding momentum from the main flow from the direction of the leading edge. The increase in the angle of attack causes bubble separation in the leading-edge gap size, which is like a pseudo-body transforming from convergent to smaller.

Comparative Study of Beam and Plate Theories for Moderate Aspect Ratio Wings

The main objective of the present study is to identify the best structural model for both aeroelastic and structural analysis of unswept rectangular wings with aspect ratios between 2 to 5. The paper presents a detailed study of the similarities and differences between the classical beam and plate theories, which provides new insight into this classical problem. To perform the aeroelastic analysis, the three-dimensional Peters aerodynamic model is coupled with classical plate theory. This combination leads to a new simpler three-dimensional aeroelastic model that can reduce the computational time. The results have been evaluated using both the unpublished and highly cited experimental data. Interestingly, by performing both structural and aeroelastic analyses, a comment can be stated that, even for relatively low aspect ratios () of thin rectangular cantilever plates, the model based on the beam theory is closer to the experimental model compared to the plate theory. This finding may be unexpected by many researchers. Also, using a novel approach, it has been shown that the most significant difference between the beam and plate theories results arises from a subtle difference in the displacement field, which has not been given attention so far.

Aerodynamic Shape Optimisation Using Parametric CAD and Discrete Adjoint

This paper presents an optimisation framework based on an open-source CAD system and CFD solver. In this work, the high-fidelity flow solutions and surface sensitivities are obtained using the primal and discrete adjoint formulations of SU2. This paper shows the direct use of CAD models for optimisation by developing a CAD system application programming interface and creating a link between the CAD-MESH-CFD analysis. A methodology to obtain geometric sensitivities is introduced, enabling the calculation of accurate gradients with respect to CAD variables and the deformation of the analysis mesh during the optimisation process. This methodology guarantees that the new surface mesh lies exactly on the CAD geometry. The optimisation framework is applied to a rectangular wing and a three section high-lift aerofoil configuration derived from the NASA CRM-HL configuration. Both geometries are created using FreeCAD. The performance objectives are to decrease the drag while constraining the lift to be above a desired value. The twist distribution of the wing was parameterised within the CAD system, allowing the minimisation of the induced drag by obtaining a nearly elliptical lift distribution. For the high-lift configuration, the position and rotation of the flap and slat were parameterised with respect to the original section; the final optimised positions yield a drag reduction of approximately 16.5%. These results show that the CAD parameterisation can be reliably used to obtain efficient optimums while operating directly on the CAD geometries.

Contribution of spanwise and cross-span vortices to the lift generation of low-aspect-ratio wings: Insights from force partitioning

This study reports on the vortex-induced lift production mechanisms in low Reynolds number flows over low aspect-ratio rectangular wings. We use a rigorous force partitioning method which allows for the estimation of the pressure-induced aerodynamic loads due to distinct flow features or vortex structures in the flow around the wing. The specific focus of this work is on distinguishing the effect of spanwise and cross-span oriented vortex structures on pressure-induced lift production. We quantify the lift induced on the wing by these different vortices, and also estimate their influence within different regions of the flow-field around the wing and in the wake. By varying the aspect-ratio and angle-of-attack of the wing, we show that for most cases, the spanwise oriented vorticity contributes less to the total lift than cross-span oriented vortices. Furthermore, the spanwise vorticity in the near wake is capable of producing net negative lift on the wing and this is explained by separating and quantifying the influence of vortex cores and regions of strain in the wake. The results demonstrate the utility of the force partitioning method for dissecting the flow physics of vortex dominated flows.

The Influence of Turbulence Models on the Numerical Modelling of a 3D Wing in Ground Effect

This paper deals with the influence of different RANS turbulence models on the numerical modelling of a 3D rectangular symmetrical wing in ground effect. Travelling near a solid surface, so-called ground effect, considerably alters the aerodynamic characteristics of a wing. This paper aims to investigate the performance of the widely used eddy viscosity turbulence models while predicting the changing aerodynamic behavior due to the ground effect. Three different RANS turbulence models, realizable , SST and Spalart-Allmaras models are taken into consideration. The effectiveness of the turbulence models were tasted in comparison with the experimental data in different angles of attack and ground heights. Results reveals that, the effect of the turbulence models on the numerical accuracy of the ground effect aerodynamics calculations are related to the altitude and the angle of attack. The choice of the turbulence model becomes important when the wing travels in very close proximity to the ground and the angle of attack is low or negative. The discrepancy of the calculated results mainly comes from the pressure distribution variations on the lower side of the wing. For high angles of attack, or relatively larger ground heights, the difference between the predictions of the turbulence models become negligible.

Review of experimental investigations of wings in ground effect at low Reynolds numbers

The ground effect-induced large lift increase and lift-induced drag reduction have long been recognized and utilized in the design and construction of wing-in-ground effect (WIG) craft. Various wing planforms have been employed in WIG craft. In this study, the experimental investigations of rectangular wings and delta wings of reverse and regular configurations at low Reynolds numbers are reviewed. For rectangular wings, both chord-dominated and span-dominated ground effects on the aerodynamics, tip vortex, and lift-induced drag are reviewed. For reverse delta wings, in addition to the experimental measurements of the aerodynamics and tip vortex flow at different ground distances, passive flow control utilizing Gurney flap, cropping, and anhedral are reviewed. The impact of ground effect on delta wings is also discussed. Suggestions for future investigations applicable to each wing planform in-ground effect are provided.

Experimental and computational investigations of aerodynamic characteristics of a finite rectangular wing-in-ground effect

Wind tunnel experiments are carried out on a 3D wing-in-ground effect at pre- and post-stall angles of attack at a relatively low Reynolds number, Re ≈ 8.8 × 104. The rectangular wing, aspect ratio, AR = 6.4 used in the present work has a symmetric airfoil section, NACA0012 and is studied at different ranges of ground proximity and also compared to a wing of cambered airfoil section, NACA4415 not in ground proximity. Unsteady and time-averaged six-component aerodynamic characteristics, coefficients of Lift, Drag, Side forces, Pitch, Roll, Yaw moments at several angles of attack in the range – 8° < α < 18° are reported. Aerodynamic efficiency and drag polars are studied in lieu of ground proximity at several angles of attack. Effect of ground proximity on the occurrence of stall and [Formula: see text] is studied. Numerical calculations using steady-state CFD are also made for quantitative comparison. The effect of ground proximity on span-wise pressure distribution and induced velocity in the vicinity of the wing is also discussed in detail.

The Aerodynamic Effect of an Alula-like Vortex Generator on a Revolving Wing.

An alula is a small structure of feathers that prevents birds from stalling. In this study, the aerodynamic effect of an alula-like vortex generator (alula-VG) on a revolving wing was investigated using the PIV technique in a water tank. The alula-VG was mounted on a rectangular wing model at two spanwise positions. The wing model with a revolving motion was installed at different angles of attack, which included pre-stall and post-stall conditions. The velocity fields around the wing model with/without an alula-VG were measured and analyzed, including the vorticity contour, the circulation of vortex structures, and the corresponding sectional lift coefficient, which are used to explain the aerodynamic effect induced by an alula-VG. The lift-off and bursting of the leading-edge vortex (LEV) affect the magnitude of the chordwise circulation and the section lift coefficient. The results show that compared to an alula-VG mounted fixed wing model, the flow interactions among the alula-VG induced spanwise flow, the inertial force caused by the revolving motion, and the wing-tip vortex play important roles in the vortex bursting and the resultant aerodynamic performance. The effect of an alula-VG on a revolving wing depends on its spanwise position and the angle of attack of a wing model, which need to be properly matched.

Plasma Gurney Flap Flight Control at Low Angle of Attack

A flight control concept without movable surfaces using electrofluidic actuators is assessed from low-speed scaled two-dimensional (2-D) rectangular wings up to three-dimensional (3-D) full-scale tapered swept wings at realistic aircraft operating conditions. The plasma Gurney flap concept consists of placing spanwise dielectric barrier discharge (DBD) plasma actuators on both sides of a wing or empennage near the trailing edge, and pointing in opposite directions, to change the flow curvature in this region, thus altering lift. Low-speed wind-tunnel tests and corresponding computational fluid dynamics (CFD) simulations are first carried out for this concept on scaled 2-D rectangular wings. Measured lift moment and flow streamlines are used to validate the simulation (CFD) tool. Simulations with this tool are then performed to assess the effect of wing taper and sweep on the effectiveness of the concept at low speed and to evaluate the concept for full-scale 3-D tapered swept-wing geometries for a single-aisle airliner. The results indicate that the plasma Gurney flap has better performance on tapered and swept wings relative to rectangular wings because of the reduction in the velocity component normal to the plasma actuator. Moreover, the presence of shocks at cruise flight conditions improves the effectiveness of the plasma Gurney flap concept.

High-Rate, High-Precision Wing Twist Actuation for Drone, Missile, and Munition Flight Control

This paper covers a new actuation and deflection controller configuration for high-aspect-ratio wings used on subsonic drones, missiles, and munitions. Current approaches to the flight control of these aircraft have unearthed challenges with friction, stiction, slop, bandwidth, and thick boundary layer nonlinearities, which degrade flight control accuracy—especially in terminal flight phases. The approach described in this paper uses directionally attached piezoelectric (DAP) actuators to actively twist a high-aspect-ratio wing for flight control. The DAP actuators were modeled analytically and computationally using linear finite element modeling. A 3″ (7.62 cm) chord × 15″ (38.1 cm) semispan rectangular wing with an NACA 0012 profile was built and structurally tested, demonstrating excellent agreement between theory and experiment. New actuation methods were used to overdrive the PZT-5H piezoelectric elements deep into the repoling range. This overdrive actuation rejuvenated the actuator elements and allowed for dramatically improved deflections with respect to configurations in previous years. Static testing demonstrated deflections in excess of ±1.6° in root-to-tip twist. Dynamic testing showed corner frequencies greater than 310 Hz. A series of wind tunnel tests at up to 180 ft/s (55 m/s, 123 mph, 107 kts, 198 kph) demonstrated excellent roll control authority, rapid manipulation of Clδ, and lift manipulation using quasi-static deflections. The paper concludes with a summary of implications for terminal guidance for drone, missile, and munition flight control in real atmospheres.

Multi-fidelity structural analysis of a beam-shaped wing

As far as integrity and proper operation of a flying vehicle are concerned, modal analysis of the wing is a crucial design procedure. This procedure aims to define the natural frequencies of the wing structure to avoid resonance under fluctuating aerodynamic loads. This procedure becomes more significant if the wing to forced to perform pitching oscillation. The present study aims to define the dynamic behavior of a rectangular wing with NACA 0009 airfoil using the Euler-Bernoulli beam theory by treating the wing as a cantilever beam. To assess the validity of this treatment and the theoretical method as a design tool, both numerical simulations and experimental measurements are applied on the wing. Results of this multi-fidelity modal analysis define the natural frequencies of the wing. The good agreement of the three methods confirms the validity of treating the wing in concern as a simple cantilever beam.

Unsteady Effects of Blowing over Actuated Surfaces Using Phase-Locked Particle Image Velocimetry

An experimental study is conducted to investigate the effects of upper-surface trailing-edge blowing on a low-aspect-ratio rectangular wing with an actively actuated flap. Two wing configurations, the wing with a baseline flap and a dual-radius flap, are wind-tunnel tested at three spanwise locations to investigate the three-dimensional and unsteady effects of blowing during flap actuation at a freestream Reynolds number (based on the airfoil chord) of . Two-dimensional and stereoscopic phase-locked particle image velocimetry (PIV) measurements are used to collect data during flap actuation at different actuation speeds and blowing intensities. Proper orthogonal decomposition and modified Q criterion are used to analyze the PIV data. The wake dynamics reveal that flap actuation contributes to tip-vortex strengthening when active blowing is not present. The combination of flap actuation and active continuous blowing is more effective in controlling the boundary layer compared to the flap at rest for the same blowing intensities.

Development and interaction of vortices over a very low aspect-ratio wing under pitch-up motion

The vortical structures over a thin rectangular wing with a very low aspect ratio of 0.277 were investigated in a wind tunnel at an effective Reynolds number of $3 \times 10^6$ . When applying pitch-up motion pivoted at mid-chord, the maximum lift angle was increased with an increase in the pitch rate, but the maximum lift coefficient was reduced. The pitching motion also caused delay in the vortical development over the wing, which was increased with an increase in the pitch rate. The delay in the leading-edge vortex development due to the pitching motion was nearly identical to that in the tip vortex development, indicating that the dynamics of the leading-edge vortex was strongly influenced by the tip vortex. This was confirmed by particle image velocimetry measurements, which demonstrated that the tip vortex over a very low aspect-ratio wing induced strong downwash to influence the development of the leading-edge vortex during the pitching motion, which led to a delay in flow separation.

Nonlinear Aerodynamic Model in Dynamic Ground Effect at High Angles of Attack

This paper focuses on the development of a model to represent the longitudinal aerodynamics of a wing and/or flight vehicle in ground effect when height is a function of time including high angles of attack. A general aerodynamic model of a wing and/or airplane in ground effect that includes high angles of attack was created. The aerodynamic coefficients of wings studied herein were obtained by the unsteady vortex-lattice method with Kirchhoff-based correction (UVLM-K). The wind-tunnel measurements presented in the literature were used to validate the UVLM-K. Then, a rectangular wing was simulated at high angles of attack in takeoff and flare, and the aerodynamic characteristics at different heights above ground were obtained along with the derivatives during these maneuvers. The mathematical model presented herein is capable of modeling unsteady aerodynamic phenomena in ground effect at high angles of attack. When this model was used in the static ground effect, values of equal to or greater than 0.999, 0.981, and 0.993 were obtained for lift, induced drag, and pitching moment coefficients, respectively. In the dynamic ground effect, the model can adjust the aerodynamic coefficient during the maneuvers.

Flutter of a finite rectangular Wing’D mill in pitch and heave

Exact solutions of flutter are explored for a mode suitable for an oscillating 2D hydrofoil version of the summarised FlutterWing windpump which radically surpasses the old rotary fanpump. The imaginary part G of the 1D Theodorsen wake lift factor T rises singularly from the steady to allow 1D pure pitch flutter around the leading edge at low frequency. But its logarithmic infinite negative pitch damping by the shed vorticity is capped by the log of the 2D span. The downwash of an oscillating trailing (tip) vortex is reduced by a function of the reduced frequency based on spanwise distance. Its lag damps pitch and further raises the pitch unstable aspect ratio A to above 36. All binary pitch & heave neutral flutter frequency contours in (inertia, imbalance) space still pass through a nexus of the same total pitch inertia and imbalance as the corrected virtual mass concentrated at ¾ chord, a very high total in water. The internal bound windwise vortex from ¼ chord to trailing edge reduces as A−2 the 1D lift slope at all frequencies. It expands the 1D T = ½ double root of high frequency elliptical contours kissing the low frequency limit line at the nexus to make them dip below the line to the right of the nexus as hyperbolae with the nexal ray as left asymptote. Thus low A discovers a new wedge of high frequency binary flutter with real mass moments less than the virtual, as in water.

Unsteady aerodynamic analysis and effectiveness of bio-inspired flapping wings in V-formation flight

Several bird species have been observed to fly in V-formation, an arrangement which exploits aerodynamic features to allow the group to conserve energy when migrating over long distances without stopping and feeding. The use of such grouping arrangement and organized pattern has demonstrated longer endurance and less power consumption in comparison with single flights. In this work, a computationally efficient potential flow solver based on the unsteady vortex lattice method (UVLM) is employed to assess the aerodynamic performance of flapping wings in forward flight in terms of lift and thrust generation along with the propulsive efficiency. The UVLM has the capability to simulate incompressible and inviscid flows over moving thin wings where the separation lines are known a priori. A bio-inspired, albatross wing shape is considered and its aerodynamic performance in formation flights is compared against conventional elliptical and rectangular wing shapes. The aerodynamic analysis is carried out for different wing arrangements of 3-body and 5-body V-formations to determine the optimal spacing parameters leading to maximum propulsive efficiency. The simulation results reveal that, at the optimal formation angle and separation distance, the albatross-inspired wing shape produces the most lift over the flapping cycle, while the rectangular wing shape generates the most thrust over the flapping cycle. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a 5-body V-formation utilizing the albatross wing shape with a separation distance set to one-third of the span and a formation angle set to 139°. The present study provides guidance for the design of multi-flapping wing air vehicles based on the expected flight mission. The albatross wing shape is found to have superior capability in producing lift, while the elliptical wing shape is observed to consume less power. The rectangular wing shape is found to produce higher thrust and then can achieve faster forward motion.