Aerodynamic Benefits Research Articles

Static Structural Analysis of a Variable Span Morphing Wing for Unmanned Aerial Vehicle

While the primary reason to develop an adaptive wing is the aerodynamic benefits, the primary hindrance is the structural and vibrational considerations due to the unsteady nature of the airflow during the flight. Hence this study forms an important part of the morphable wing technology. In this paper, the design of a moderate aspect ratio variable span wing will be performed. The morphing wing is modeled structurally to observe the effect of spanwise load distribution on the wing structure. For the structural design and analysis of the unmanned aerial vehicle (UAV) under this study, commercial software Solidworks and Ansys/Static Structural/Modal are used. The static structural analyses of the wing are performed under different load conditions. The results of these analyses show that the designed structure is safe within the flight envelope. It is observed that the wing-root bending moment increases drastically due to an increase in the wingspan. Thus, the bending moment along the wingspan of the morphing wing is much larger than that of the conventional wing which results in an increase in the deflection of the free-end. The maximum stress for the un-extended wing configuration increases for the extended wing configuration.

FLOW CONTROL USING MOVING SURFACE AT THE LEADING EDGE OF AEROFOIL

Flow control is a significant topic of research in the field of aviation. Researchers in this field are continuously trying their best to find various flow control strategies in order to extract aerodynamic benefits by applying them. Applying moving surface at the leading edge of aerofoil is a type of strategy among the various types of active flow control strategies. In the present research work a rotating cylinder is added on the leading edge of the aerofoil as a moving surface in order to control the flow over its surface. The moving surface boundary layer control is applied to NACA 0018 airfoil for investigating its aerodynamic benefits and effectiveness. The moving surface is created by rotating a smooth cylinder at the leading edge of the aerofoil. The peripheral velocity of the cylinder injects momentum to the upper surface boundary layer of the aerofoil and thus delays its separation. This results in the gain in both the maximum lift coefficient and the stall angle. The work has been done at four different Reynolds Number i.e., at Re = 1.4 X 10^5, 1.85 X 10^5, 2.3 X 10^5, 2.8 X 10^5 at different angles of attack.

Numerical Simulation of a Passive Control of the Flow Around an Aerofoil Using a Flexible, Self Adaptive Flaplet

Self-activated feathers are used by almost all birds to adapt their wing characteristics to delay stall or to moderate its adverse effects (e.g., during landing or sudden increase in angle of attack due to gusts). Some of the feathers are believed to pop up as a consequence of flow separation and to interact with the flow and produce beneficial modifications of the unsteady vorticity field. The use of self adaptive flaplets in aircrafts, inspired by birds feathers, requires the understanding of the physical mechanisms leading to the mentioned aerodynamic benefits and the determination of the characteristics of optimal flaps including their size, positioning and ideal fabrication material. In this framework, this numerical study is divided in two parts. Firstly, in a simplified scenario, we determine the main characteristics that render a flap mounted on an aerofoil at high angle of attack able to deliver increased lift and improved aerodynamic efficiency, by varying its length, position and its natural frequency. Later on, a detailed direct numerical simulation analysis is used to understand the origin of the aerodynamic benefits introduced by the flaplet movement induced by the interaction with the flow field. The parametric study that has been carried out, reveals that an optimal flap can deliver a mean lift increase of about 20% on a NACA0020 aerofoil at an incidence of 20o degrees. The results obtained from the direct numerical simulation of the flow field around the aerofoil equipped with the optimal flap at a chord Reynolds number of 2 × 104 shows that the flaplet movement is mainly induced by a cyclic passage of a large recirculation bubble on the aerofoil suction side. In turns, when the flap is pushed downward, the induced plane jet displaces the trailing edge vortices further downstream, away from the wing, moderating the downforce generated by those vortices and regularising the shedding cycle that appears to be much more organised when the optimal flaplet configuration is selected.

On the high-lift characteristics of a bio-inspired, slotted delta wing

A bio-inspired, slotted delta wing was abstracted from a multi-vane propulsor geometry ubiquitous in nature, and analysed to investigate aerodynamic performance during acceleratory and steady-state motions. Evolutionary convergence of slotted geometries in nature suggests an aerodynamic benefit in manoeuvrability, as exemplified in the fins and wings of a broad range of extant and extinct swimmers and flyers, respectively. Through direct force measurements and stereoscopic particle image velocimetry, it was found that the abstracted, slotted geometry exhibited a region of steady-state lift and drag enhancement at angles of attack greater than 25° when compared to a reference profile based on a delta-wing plate. At an angle of attack of 30°, the lift and drag measured on the abstracted model were 15.3% and 17.0% higher than the delta-wing model, respectively. In contrast, these shapes showed little difference in performance during an acceleration-from-rest manoeuvre. It was found that the secondary and tertiary vanes of the abstraction encouraged the formation of additional leading-edge vorticity. The formation of these additional leading-edge vortices was confirmed by an increase in streamwise circulation measured near each effective leading edge along the length of the chord. As such, this configuration provides lift augmentation appropriate for the development of high-performance control surfaces.

Computational Investigation of a Boundary-Layer-Ingestion Propulsion System

The present paper examines the potential propulsive and aerodynamic benefits of integrating a boundary-layer ingestion propulsion system into the Common Research Model geometry and the NASA tetrahedral unstructured software system. The numerical propulsion system simulation environment is used to generate engine conditions for computational fluid dynamics analyses. Improvements to the boundary-layer ingestion geometry are made using the constrained direct iterative surface curvature design method. The potential benefits of the boundary-layer ingestion system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the boundary-layer ingestion geometric design are shown, and improvements between subsequent boundary-layer ingestion designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 ft, with a Reynolds number of 40 million based on the mean aerodynamic chord and an angle of attack of 2 deg for all geometries. The results indicate an 8% reduction in engine power requirements at cruise for the boundary-layer ingestion configuration as compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using constrained direct iterative surface curvature are shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately 12 counts over the baseline geometry.

Shape Memory Alloy Enables Folding Wings in Flight

Abstract The Spanwise Adaptive Wing project intends to obtain a wide spectrum of aerodynamic benefits in flight by folding wings through the use of an innovative and lightweight shape memory alloy.

Distributed Propulsion Aircraft with Aeroelastic Wing Shaping Control for Improved Aerodynamic Efficiency

This study presents an aeroelastic wing shaping control concept for distributed propulsion aircraft. By leveraging wing flexibility, wing-mounted distributed propulsion can be used to re-twist wing shapes in-flight to improve aerodynamic efficiency. A multidisciplinary approach is used to develop an aero-propulsive-elastic model of a highly flexible wing distributed propulsion transport aircraft. The conceptual model is used to evaluate the aerodynamic benefit of the distributed propulsion aircraft. The initial conceptual analysis shows that an improvement in the aerodynamic efficiency quantity of lift-to-drag ratio is possible with the proposed aeroelastic wing shaping control for distributed propulsion aircraft. Two concepts are studied: single-generator configuration and dual-generator configuration with four propulsors per wing. The baseline aircraft model is NASA Generic Transport Model. A fan performance analysis is developed for propulsion sizing. Cruise performance analysis is conducted to evaluate the potential improvement in the cruise range for the configurations under study. A flutter analysis is performed to address the potential flutter issue as the propulsors are placed toward the wing tip, which would cause a reduction in the wing natural frequencies. Flight control considerations are addressed in the context of the engine-out requirement, yaw and roll controls, and yaw damping augmentation using differential thrust.

Stereotypy of group flight in Brazilian free-tailed bats

Many bats form colonies and undergo nightly emergence in dense, fast-moving streams. Although the flight mechanics of individual bats have been well studied, the effect of flying in a group has not been studied with large aggregations under natural conditions. We tested the hypothesis that group size affects flight mechanics and behaviour in Brazilian free-tailed bats, Tadarida brasiliensis . We measured the flight path, flight path time and wing beat rate of individual bats by analysing videos of bats in flight and compared values across different flight group sizes. Flight path, flight speed and wing beat rate of individual bats were all unaffected by group size. Additionally, bats maintained a constant wing beat rate regardless of flight speed. These results suggest that Brazilian free-tailed bats experience neither an aerodynamic benefit nor a cost to travelling in groups.

Boundary Layer Ingestion Benefit of the D8 Transport Aircraft

This paper presents the experimental assessment of the aerodynamic benefit of boundary layer ingestion for an advanced design civil transport aircraft, the D8 “double bubble,” carried out from 2010 to 2015 as part of a NASA Phase 2 Program. A back-to-back comparison of non-boundary layer ingesting and boundary layer ingesting versions of the D8 was conducted using 1:11-scale powered models in the NASA Langley 14- by 22-foot subsonic tunnel. The aerodynamic benefit of boundary layer ingestion, as quantified by the difference in mechanical flow power required with boundary layer ingestion relative to the non-boundary layer ingesting case, was measured using two different methods to be 8.6% at the simulated cruise condition when the same propulsors are used on the two configurations. The benefit is found to be insensitive to the various modeling and processing assumptions. A detailed error analysis shows that the benefit has an uncertainty fraction of 0.21 and a 95% confidence interval fraction of 0.035, thus giving high confidence to these results. This work represents the first measurement of boundary layer ingestion performance improvements for a realistic civil aircraft configuration and provides a proof-of-concept for the use of boundary layer ingestion to improve fuel efficiency of subsonic transports.

Stall Recovery of a Morphing Wing via Extended Nonlinear Lifting-Line Theory

Aircraft morphing provides advantages to traditional flight including drag reduction and maneuverability. Previous research indicates that smooth spanwise transitions in trailing-edge camber, representative of a biological analog, provide aerodynamic benefits at small angles of attack by eliminating vortices at geometric discontinuities but lack nonlinear aerodynamic investigations. This work aims to analyze the adaptability of a spanwise morphing wing concept with respect to nonlinear aerodynamics using an optimized nonlinear extended lifting-line model. In this novel approach, it is shown that adaptation, including stall recovery, can be achieved solely through geometric tailoring as opposed to attitude correction for a range of flight conditions while reducing the drag penalty associated with operating at the unadapted condition. The range of conditions for which the wing can recover are restricted by the limited trailing-edge deflections and the inability of the actuators to substantially shift the stall angle of the section lift curve. These results provide insight into improving morphing wing designs, indicating that, by adding another degree of freedom to the chordwise deformation such as a morphing hinge capable of larger actuation and reflex camber, stall recovery via geometric tailoring may be feasible for an even larger range of conditions.

Effects of Tip Gap Size on the Aerodynamic Performance of a Cavity-Winglet Tip in a Turbine Cascade

The aerodynamic performance of a cavity-winglet tip is investigated in a high-pressure turbine cascade by experimental and numerical methods. The winglet tip has geometric features of a cavity and a suction side fore-part winglet. A cavity tip is studied as the baseline case. The aerodynamic performances of the two tips are investigated at three tip gaps of 0.8%, 1.7%, and 2.7% chord. At tip gaps of 1.7% and 2.7% chord, the loss near the blade tip is dominated by the tip leakage vortex (TLV) for both tips, and the winglet tip mainly reduces the loss generated by the tip leakage vortex. In the past, it was concerned that at a small tip gap, the winglet tip could introduce extra secondary loss and show little aerodynamic benefits. The winglet tip used in the current study is also found to be able to effectively reduce the loss at the smallest tip gap size of 0.8% chord. This is because at this small tip gap, the tip leakage vortex and the passage vortex (PV) appear simultaneously for the cavity tip. The winglet tip is able to reduce the pitchwise pressure gradient in the blade passage, which tends to suppress the formation of the passage vortex. The effects of the winglet tip on the flow physics and the loss mechanisms are explained in detail.

Analytical Study of Articulating Turbine Rotor Blade Concept for Improved Off-Design Performance of Gas Turbine Engines

Gas turbine engines are generally optimized to operate at nearly a fixed speed with fixed blade geometries for the design operating condition. When the operating condition of the engine changes, the flow incidence angles may not be optimum with the blade geometry resulting in reduced off-design performance. Articulating the pitch angle of turbine blades in coordination with adjustable nozzle vanes can improve performance by maintaining flow incidence angles within the optimum range at all operating conditions of a gas turbine engine. Maintaining flow incidence angles within the optimum range can prevent the likelihood of flow separation in the blade passage and also reduce the thermal stresses developed due to aerothermal loads for variable speed gas turbine engine applications. U.S. Army Research Laboratory (ARL) has partnered with University of California San Diego and Iowa State University Collaborators to conduct high fidelity stator–rotor interaction analysis for evaluating the aerodynamic efficiency benefits of articulating turbine blade concept. The flow patterns are compared between the baseline fixed geometry blades and articulating conceptual blades. The computational fluid dynamics (CFD) studies were performed using a stabilized finite element method developed by the Iowa State University and University of California San Diego researchers. The results from the simulations together with viable smart material-based technologies for turbine blade actuations are presented in this paper.

Effects of rotor blade-tip geometry on helicopter trim and control response

ABSTRACTFor performance improvement and noise reduction, swept and anhedral tips have been incorporated in advanced-geometry rotor blades. While there are aerodynamic benefits to these advanced tip geometries, they come at the cost of complicated structural design and weight penalties. The effect of these tip shapes on loads, vibration and aeroelastic response are also unclear. In this study, a comprehensive helicopter aeroelastic analysis which includes rotor-fuselage coupling shall be described and the analysis results for rotor blades with straight tip, tip sweep and tip anhedral shall be presented and compared. The helicopter modelled is a conventional one with a hingeless single main rotor and single tail rotor. The blade undergoes flap, lag, torsion and axial deformations. Tip sweep, pretwist, precone, predroop, torque offset and root offset are included in the model. Aerodynamic model includes Peters-He dynamic wake theory for inflow and the modified ONERA dynamic stall theory for airloads calculations. The complete 6-dof nonlinear equilibrium equations of the fuselage are solved for analysing any general flight condition. Response to pilot control inputs is determined by integrating the full set of nonlinear equations of motion with respect to time. The effects of tip sweep and tip anhedral on structural dynamics, trim characteristics and vehicle response to pilot inputs are presented. It is shown that for blades with tip sweep and tip anhedral/dihedral, the 1/rev harmonics of the root loads reduce while the 4/rev harmonics of the hub loads increase in magnitude. Tip dihedral is shown to induce a reversal of yaw rate for lateral and longitudinal cyclic input.

Basal paravian functional anatomy illuminated by high-detail body outline

Body shape is a fundamental expression of organismal biology, but its quantitative reconstruction in fossil vertebrates is rare. Due to the absence of fossilized soft tissue evidence, the functional consequences of basal paravian body shape and its implications for the origins of avians and flight are not yet fully understood. Here we reconstruct the quantitative body outline of a fossil paravian Anchiornis based on high-definition images of soft tissues revealed by laser-stimulated fluorescence. This body outline confirms patagia-bearing arms, drumstick-shaped legs and a slender tail, features that were probably widespread among paravians. Finely preserved details also reveal similarities in propatagial and footpad form between basal paravians and modern birds, extending their record to the Late Jurassic. The body outline and soft tissue details suggest significant functional decoupling between the legs and tail in at least some basal paravians. The number of seemingly modern propatagial traits hint that feathering was a significant factor in how basal paravians utilized arm, leg and tail function for aerodynamic benefit.

Bristles reduce the force required to 'fling' wings apart in the smallest insects.

The smallest flying insects commonly possess wings with long bristles. Little quantitative information is available on the morphology of these bristles, and their functional importance remains a mystery. In this study, we (1) collected morphological data on the bristles of 23 species of Mymaridae by analyzing high-resolution photographs and (2) used the immersed boundary method to determine via numerical simulation whether bristled wings reduced the force required to fling the wings apart while still maintaining lift. The effects of Reynolds number, angle of attack, bristle spacing and wing-wing interactions were investigated. In the morphological study, we found that as the body length of Mymaridae decreases, the diameter and gap between bristles decreases and the percentage of the wing area covered by bristles increases. In the numerical study, we found that a bristled wing experiences less force than a solid wing. The decrease in force with increasing gap to diameter ratio is greater at higher angles of attack than at lower angles of attack, suggesting that bristled wings may act more like solid wings at lower angles of attack than they do at higher angles of attack. In wing-wing interactions, bristled wings significantly decrease the drag required to fling two wings apart compared with solid wings, especially at lower Reynolds numbers. These results support the idea that bristles may offer an aerodynamic benefit during clap and fling in tiny insects.

Optimization of Flexible Wings with Distributed Flaps at Off-Design Conditions

An efficient process to aerodynamically optimize transport wings while addressing static aeroelastic effects is presented. The process is used to assess the aerodynamic performance benefits of a full-span trailing-edge flap system on a generic transport aircraft at off-design conditions. To establish a proper baseline, a transport wing is first aerodynamically optimized at a midcruise flight condition. The optimized wing is then analyzed at several off-design cruise conditions. The aerodynamic optimization is repeated at these off-design conditions to determine how much performance is lost by the wing optimized solely for the midcruise condition. The full-span flap system is then adapted to maximize performance of the midcruise-optimized wing at each off-design condition. The improvement due to the trailing-edge flaps is quantified by examining the degree to which the flaps can recover the performance of a wing designed specifically for the off-design condition. To evaluate the repercussions of aeroelasticity on the effectiveness of the flap system, this entire process is performed on both a conventional stiff wing and a modern, more flexible wing. The impact of the choice of flap layout is also explored. The results indicate that the flap system allows for significant improvement in performance throughout cruise and that it can be advantageous even for wings with increased flexibility. Moreover, the flaps appear to provide a means for active wave drag reduction during flight.

Effect of airfoil leading edge waviness on flow structures and noise

Purpose– The tubercles at the leading edge of Humpback Whale flippers have been shown to increase aerodynamic efficiency. The purpose of this paper is to compute the flow structures and noise signature of a NACA0012 airfoil with and without leading edge waviness, and located in the wake of a cylinder using the hybrid RANS-LES method.Design/methodology/approach– The mean flow Mach number is 0.2 and the angle of attack used is 2°. After benchmarking the method using existing experimental results, unsteady computations were then carried-out on both airfoil geometries and for a 2° angle of attack.Findings– Results from these computations confirmed the aerodynamic benefits of the leading edge waviness. Moreover, the wavy leading edge airfoil was found to be at least 4 dB quieter than its non-wavy counterpart. In-depth analysis of the computational results revealed that the wavy leading edge airfoil breaks up the large coherent structures which are then convected at higher speeds down the trough region of the waviness in agreement with previous experimental observations. This result is supported by both the two-point and space-time correlations of the wall pressure.Research limitations/implications– The limitations of the current findings reside in the fact that both the Reynolds number and the flow Mach number are low, therefore not applicable to aircrafts. In order to extend the study to practical aircrafts one needs huge grids and large computational resources.Practical implications– The results obtained here could have a huge implications on the design of future aircrafts and spacecrafts. More specifically, the biggest benefit from such redesign is the reduction of acoustic signature as well as increased efficiency in fuel consumption.Social implications– Reducing acoustic signature from aircrafts has been a major research thrust for NASA and Federal Aviation Administration. The social impact of such reduction would be improved quality of life in airport communities. For military aircrafts, this could results in reduced detectability and hence saving lives.Originality/value– Humpback Whales have been studied by various researchers to understand the effects of leading edge “tubercles” on flow structures. What is new in this study is the numerical confirmation of the effects of the tubercles on the flow structures and the resulting noise radiations. It is shown through the use of two-point correlations and space-time correlations that the flow structures in the trough area are indeed vortex tubes.

Morphing aircraft based on smart materials and structures: A state-of-the-art review

A traditional aircraft is optimized for only one or two flight conditions, not for the entire flight envelope. In contrast, the wings of a bird can be reshaped to provide optimal performance at all flight conditions. Any change in an aircraft’s configuration, in particular the wings, affects the aerodynamic performance, and optimal configurations can be obtained for each flight condition. Morphing technologies offer aerodynamic benefits for an aircraft over a wide range of flight conditions. The advantages of a morphing aircraft are based on an assumption that the additional weight of the morphing components is acceptable. Traditional mechanical and hydraulic systems are not considered good choices for morphing aircraft. “Smart” materials and structures have the advantages of high energy density, ease of control, variable stiffness, and the ability to tolerate large amounts of strain. These characteristics offer researchers and designers new possibilities for designing morphing aircraft. In this article, recent developments in the application of smart materials and structures to morphing aircraft are reviewed. Specifically, four categories of applications are discussed: actuators, sensors, controllers, and structures.

English

A novel nonplanar wing concept called C-Wing is studied and implemented on a commercial aircraft to reduce induced drag which has a significant effect on fuel consumption. A preliminary sizing method which employs an optimization algorithm is utilized. The Airbus A320 aircraft is used as a reference aircraft to evaluate design parameters and to investigate the C-Wing design potential beyond current wing tip designs. An increase in aspect ratio due to wing area reduction at 36m span results in a reduction of required fuel mass by 16%. Also take-off mass savings were obtained for the aircraft with C-Wing configuration. The effect of a variations of height to span ratio (h/b) of C-Wings on induced drag factor k, is formulated from a vortex lattice method and literature based equations. Finally the DOC costing methods used by the Association of European Airlines (AEA) was applied to the existing A320 aircraft and to the C-Wing configuration obtaining a reduction of 6% in Direct Operating Costs (DOC) for the novel concept resulted. From overall outcomes, the C-Wing concept suggests interesting aerodynamic efficiency and stability benefits.

Aerodynamic benefit for a cyclist by a following motorcycle

In recent years, many accidents have occurred between cyclists and in-race motorcycles, even yielding fatal injuries. The accidents and the potential aerodynamics issues have impelled the present authors to perform dedicated wind-tunnel measurements and Computational Fluid Dynamics (CFD) simulations to assess cyclist drag reduction when followed by one, two or three motorcycles. The 3D steady-state Reynolds-Averaged Navier–Stokes simulations with the standard k–ε model are validated by the wind-tunnel tests. The cyclist drag reduction goes up to 8.7% for a single trailing motorcycle and to 13.9% for three trailing motorcycles at a distance of 0.25m behind the cyclist. This distance is not uncommon in elite races, as evidenced by the many recent accidents. The effect by a single following motorcycle at realistic short distances d=0.25m (8.7%), d=0.5m (6.4%) and d=1m (3.8%) is larger than that by a following car at realistic short distance d=5m (1.4%). Therefore it could be argued that in-race motorcycles are not only more dangerous but also aerodynamically more influential. This study reinforces the necessity for the International Cycling Union to change the rules concerning in-race motorcycles, not only to avoid accidents but also to avoid unwanted aerodynamic benefits.