Improvement Of Aerodynamic Efficiency Research Articles

Morphing wing design of truss-braced-wing aircraft through aerodynamic shape optimization using the adjoint method

It is still a challenge to evaluate the benefits of the morphing wing concept with a truss-braced wing wing–body–tail configuration. To address this problem, first, a fair baseline configuration is obtained with a multipoint optimization over six flight conditions. Then, three types of morphing wing design are investigated and compared based on the baseline shape. The results indicate that the simplified variable-camber continuous trailing-edge flap system has the smallest and limited benefit, with only a 0.70% weighted aerodynamic efficiency improvement, which may not be sufficient to cover the extra burden of the increased complexity and weight. The trailing-edge morphing design has a larger benefit, with an efficiency improvement of 1.73%, while the full-wing morphing design achieved the greatest benefit, with a 5.79% efficiency improvement, demonstrating the attractive aerodynamic potential and benefits of the truss-braced-wing aircraft. Further discussion on the drag-reduction sources and some design features is also presented.

Improvement in aerodynamic efficiency of trainer aircraft wing using co flow jet method

Improvement in aerodynamic efficiency of trainer aircraft wing using co flow jet method

Nanocomposites for Aircraft Applications

The steady increase in jet fuel prices in recent years has accelerated the quest for greater economy in airline operations. While improvements in aerodynamic efficiency, engine fuel efficiency, etc., have been sought, lighter and stronger materials for aircraft structural components remain a very important goal. The percentage of advanced composites, utilizing carbon fibers, in modern aircraft has reached 50 percent. The trend now is to use nano reinforcements such as graphene and carbon nanotubes to further reduce the structural weight. Due to the difficulties in fabricating nanocomposites with a high enough volume fraction of nano reinforcement, the nano reinforcements are either added to the polymer matrix or grown on the carbon fibers. The nano reinforcements are multi-functional; thus, in addition to contributing strength, they contribute to other properties such as electrical conductivity which in turn enhances the lightning strike protection, electrostatic discharge, electromagnetic shielding, etc. This paper summarizes these aspects and also describes the applications of nanocomposites in aircraft interiors, brake components, aircraft repair, etc.

Aerodynamic Exploration for Tandem Wings with Smooth or Corrugated Surfaces at Low Reynolds Number

Skin corrugation and tandem configuration are two distinct features that characterize the flow around dragonfly wings. In contrast to the smooth airfoil and single pair of wings of conventional airplanes, corrugated surfaces and tandem wings influence aerodynamics both locally and globally. In this article, several kinds of doubly- tandem wing configurations were designed, then computational investigations based on wind tunnel experiments were conducted to investigate the aerodynamic characteristics of these models. Computational simulations using in-house codes were carried out with a freestream velocity of 20 m/s at an angle of attack from −4° to 16°. Based on these computational results, the effects of airfoil thickness, surface waviness and hindwing decalage on aerodynamic characteristics were compared and presented quantitatively. Final results demonstrate that a tandem wing configuration could eliminate separation close to the trailing edge at angles of attack 8°~10°, or delay the trailing edge separation at angles of attack greater than 10°. Thus, the aerodynamic efficiency of tandem configurations could provide significant improvement compared to configurations with a single wing. The greatest percentage of aerodynamic efficiency improvement for a tandem thick configuration compared to a single thick configuration is 1376% at angle of attack 0°. Surface waviness will stall at a lower angle of attack, but will gain some aerodynamic benefit from the standing separated flow. Hindwing decalage has obvious lift enhancement for the tandem configuration. Therefore, it is concluded that the tandem configuration is attractive and promising for MAVs with flexible structures in the near future.

Aerodynamic Efficiency Improvement on a NACA-8412 Airfoil via Active Flow Control Implementation

The present paper introduces a parametric optimization of several Active Flow Control (AFC) parameters applied to a NACA-8412 airfoil at a single post-stall Angle of Attack (AoA) of 15∘ and Reynolds number Re = 68.5×103. The aim is to enhance the airfoil efficiency and to maximize its lift. The boundary layer separation point was modified using Synthetic Jet Actuators (SJA), and the airfoil optimization was carried on by systematically changing the pulsating frequency, momentum coefficient and jet inclination angle. Each case has been evaluated using Computational Fluid Dynamic (CFD) simulations, being the Reynolds Averaged Navier–Stokes equations (RANS) turbulence model employed the Spalart Allmaras (SA) one. The results clarify which are the optimum AFC parameters to maximize the airfoil efficiency. It also clarifies which improvement in efficiency is to be expected under the operating working conditions. An energy balance is presented at the end of the paper, showing that for the optimum conditions studied the energy saved is higher than the one needed for the actuation. The paper clarifies how a parametric analysis has to be performed and which AFC parameters can be initially set as constant providing sufficient previous knowledge of the flow field is already known. A maximum efficiency increase versus the baseline case of around 275% is obtained from the present simulations.

Thermal control of transonic shock-boundary layer interaction over a natural laminar flow airfoil

Implicit large eddy simulations are performed to show control of shock and boundary layer interaction over a natural laminar flow airfoil by harmonic heat transfer on the suction surface at a free-stream Mach number M∞=0.72 and angle of attack of α=0.38°, for which experimental/flight test results exist. Surface heat flux is added in a time-periodic manner with the exciter strip located at different locations in the vicinity of the shock location at x/c≈0.49 for the flow without any control. Four cases of localized excitation with Gaussian distribution centered at x/c=0.45, 0.48, 0.50, and 0.55 on the airfoil surface are considered, with a width of 10% chord. The effects of unsteady heat flux on shock strength, location, and modification of its structure are demonstrated by instantaneous and time-averaged flow quantities. Detailed vortical and entropy contour plots and numerical Schlieren indicate flow features, such as creation and propagation of Kutta waves and their interactions with the shock wave. Time-averaged load distributions reveal a shift in the location and strength of the shock, with altered lift and drag time histories. The Fourier transforms of lift and drag coefficients help explain the alteration of the strength and structures of the shock-induced unsteadiness. The imposed excitation results in an improvement of aerodynamic efficiency (lift to drag ratio). The numerical simulations follow the algorithm developed in Sengupta et al. [Comput. Fluids 88, 19–37 (2013)].

Active flow control optimisation on SD7003 airfoil at pre and post-stall angles of attack using synthetic jets

The use of Active Flow Control (AFC) technologies to modify the forces acting on streamlined bodies is one of the most active research fields in aerodynamics. For each particular application, finding the optimum set of AFC parameters which maximises lift, minimises drag or maximises lift-to-drag ratio (aerodynamic efficiency), has become a necessary design requirement. In the present paper, the AFC technology was applied to the Selig-Donovan 7003 (SD7003) airfoil at Reynolds number 6×104. Synthetic jets were employed to modify the lift and drag forces acting on the airfoil. Four angles of attack (AoA) of 4∘, 6∘, 8∘ and 14∘ were considered, alongside five AFC parameters: jet position, jet width, momentum coefficient, forcing frequency and jet inclination angle. A multi objective optimisation based on genetic algorithms (GA) was performed for each angle of attack to find the optimum combination of AFC parameters. Each GA generation was simulated using Computational Fluid Dynamics (CFD). A home-made GA package was linked with a mesh generator and the CFD solver, and the results were automatically fed back to the GA code. Over 2200 CFD simulations were performed in two dimensions, using the Spalart-Allmaras turbulent model. The motivation behind the current study is to understand the dependence of the optimum set of AFC parameters on the AoA. Results show that, as AoA is increased, the potential benefits of AFC become more pronounced, which allows for considerable improvement in aerodynamic efficiency. The physics involved in the interaction between the main flow and synthetic jet are clearly presented and clarifies that the physical phenomenon to obtain maximum efficiency is completely different at pre-stall and post-stall AoA. In particular, the aerodynamic efficiency was increased by 251% from baseline (no actuation) by using a moderate/finite momentum coefficient at AoA=14∘, while a mere 39% increase was obtained at AoA=8∘. In addition, the interaction between the incoming flow and the synthetic jet pulsating flow at different injection angles has been thoroughly investigated.

Effect of Airfoil-Preserved Undulation Placement on Wing Performance and Wingtip Vortex

The effect of undulation placement (leading edge, trailing edge, or leading and trailing edges) on the wing performance and the wingtip vortex was investigated. Experiments were performed at the University of Dayton Low-Speed Wind Tunnel on undulated wings where the NACA 0012 airfoil cross section is preserved along the wingspan. Sensitivity studies were done on the undulation wavelength along the span (, 0.21, and 0.15) and undulation placement (leading edge, trailing edge, and both leading and trailing edges). The leading-edge undulations delayed stall until higher angles of attack; however, the maximum aerodynamic efficiency was reduced. The trailing-edge undulated wing, on the other hand, increased the maximum aerodynamic efficiency but was not successful in stall mitigation. Wings with both leading- and trailing-edge undulations showed improvement in aerodynamic efficiency as well as delayed stall. The effect of the undulations on the wingtip vortex was also investigated through Particle Image Velocimetry. For the same coefficient of lift, the undulated wing cases reduced the wingtip vortex circulation by 25%. Investigations into the wingtip vortex core RMS and aerodynamic efficiency revealed a direct relationship where a higher vortex core rms resulted in a higher aerodynamic efficiency, and vice versa.

Performance analysis of hybrid electric and distributed propulsion system applied on a light aircraft

Aircraft industry is still in the early stages of pure electric propulsion systems development, the main concern is the significant mass of batteries. As such, hybrid electric systems have gained much stakeholder attention in the recent years. At the same time, interest in distributed propulsion systems is also increasing, due to the improvement in aerodynamic efficiency compared to conventional configurations. This paper investigates these two fields, presenting the results of two correlated studies. The first study deals with:i. The relevance of the purely electric propulsion systems and their comparison to conventional ones andii. Hybrid propulsion systems and the suitable hybrid configuration for light aircraft using the normalized range factor and range analysis.The outcome of the first investigation has been used in the second study to build a distributed propulsion architecture and complete a comparative CFD analysis to demonstrate the advantages of the new concept compared to the baseline configuration.

Comparative study of two lay-up sequence dispositions for flexible skin design of morphing leading edge

Morphing leading edge has great potential for noise abatement and aerodynamic efficiency improvement. The drooping effect is realized by bending of the flexible skin which encloses to form the leading edge. Since the flexible skin is often made of composite laminates of Glass Fiber Reinforced Plastics (GFRP), the lay-up sequences have become the determinant, which affects not only the morphing quality but also the manufacturing complexity. Two optimizing methods of lay-up sequences are comparatively studied. In the first method, the laminal quantities in 0°, ±45° and 90° vary independently, while in the second one, the concept of isotropic laminate unit [0/45/−45/90]s is employed and the unit quantity is the unique variable. Final evaluation demonstrates that for both methods there is insignificant impact to the overall morphing quality; however, specific concern is equally necessary for these two methods to the tip of the leading edge where the skin is at its minimum thickness and bears the most severe bending deformation. In terms of computational efficiency and post-processing labor, the second method has better performance.

Commercialization of a Diffuser Augmented Wind Turbine for Distributed Generation

Small-scale distributed wind generation faces challenges in being cost competitive due to recent advances in solar photovoltaic and battery storage technology. Reductions in levelized cost of energy (LCOE) can be achieved by improvements in aerodynamic efficiency, generator controller design, or reducing cost of manufacture. In this paper we present a case study detailing the commercialization of a novel 200 W high-efficiency diffuser augmented wind turbine (DAWT). Results include increased rotor efficiency, bespoke controller design, and the novel use of manufacturing processes. Findings and conclusions are of direct interest to small wind turbine designers as they seek to reduce LCOE.

Passive flow control for drag reduction in vehicle platoons

The use of passive ducting from the vehicle nose out of the front wheel opening was studied as a method of modifying the wake profile of a NASCAR Xfinity Series race vehicle to influence its effect on the drag of a trailing vehicle. Utilizing a fixed inlet area due to geometric constraints, exit angle, height and exit/inlet area ratio were explored using multi-vehicle Computational Fluid Dynamics (CFD) simulations and wind tunnel validation. Results indicate that appropriately positioned ducts reduce trailing car drag throughout the range of vehicle spacing studied; most significantly, it reduces the drag peak for the trailing car at approximately 1/4 to 1/2 car length spacing. Increased exit area is shown to enhance drag reduction for the trailing car at all vehicle spacings. Increasing exit angle closer to perpendicular to the direction of travel was shown to be effective as well, even being capable of eliminating the drag peak for the trailing car. Aerodynamic efficiency was increased over the non-ducted baseline configuration with the duct exit angle nearer to the direction of travel, while it was negatively impacted with the duct exit angle perpendicular to the direction of travel. Wind tunnel testing confirmed that aerodynamic efficiency improvement was due to an increase in negative lift under the car, while Kiel probe measurements validated the shape and positioning of the wake changes caused by the ducts.

Effect of square dimples on the temperature distribution and heat transfer coefficient of an NACA0012 airfoil

ABSTRACTThe thermal boundary layer is the barrier for convective heat transfer, since the temperature within the thermal boundary layer is lower than the free stream temperature; therefore, it is preferable to maintain a small thermal boundary layer thickness (δt). Among the various categories of dimples like square, rectangle and triangle we considered square dimples for the upper surface of the NACA0012 wing throughout the span. The dimples increase the coefficient of lift due to delayed flow separation. The skin friction coefficient improvement reduces the δh which in turn reduces the (δt), therefore the rate of heat transfer is increased and surface temperature distribution becomes smooth. Dimples also act as fins, reducing the upper surface temperature to lower than the lower surface, which in turn increases the lift particularly in low-speed and micro-scale airfoils [Kim, Jongmin, Zvi Rusak, and Nikhil Koratkar. 2003. ‘Small-Scale Airfoil Aerodynamic Efficiency Improvement by Surface Temperature and Heat Transfer.’ AIAA Journal 41 (11): 2105–2113].

Glider fuselage-wing junction optimization using CFD and RBF mesh morphing

Purpose The present paper aims to address the description of a numerical optimization procedure, based on mesh morphing, and its application for the improvement of the aerodynamic performance of an industrial glider which suffers of a large separation occurring in the wing–fuselage junction region at high incidence angles. Design/methodology/approach Shape variations were applied to the baseline configuration through a mesh morphing technique founded on the mathematical framework of radial basis functions (RBF). The aerodynamic solutions were obtained coupling an RANS code with the mesh morphing tool RBF Morph™. Two shape modifiers were set up to generate a parametric numerical model. An optimization procedure, based on a design of experiment sampling, was set up implementing the fully automated workflow within a high performance computing (HPC) environment. The optimal candidates maximizing the aerodynamic efficiency were identified by means of a cubic RBF response surface approach. Findings The separation was significantly reduced, modifying the local geometry of fuselage and fairing and maintaining the wing aerofoil unchanged. A relevant aerodynamic efficiency improvement was finally gained. Practical implications The developed procedure proved to be a very powerful and efficient tool in facing aerodynamic design problems. However, it might be computationally very expensive if a large number of design variables are adopted and, in those cases, the method can be suitably used only within the HPC environment. Originality/value Such an optimization study is part of an explorative set of analyses that focused on better addressing the numerical strategies to be used in the development of the EU FP7 Project RBF4AERO.

Effect of winglets induced tip vortex structure on the performance of subsonic wings

This paper presents the comparative study of the effectiveness of three different winglet designs in reducing lift induced drag by changing the number of vortices and vortex distribution at the wingtip and correlating it to the aerodynamic characteristics of the baseline wing. The best three winglet geometries are appended to wings of different aspect ratio to further study their effectiveness in reducing drag and augmenting the lift coefficient. Computational simulations were performed on Ansys Fluent V15 using the Reynolds Averaged Navier–Stokes equations coupled with the k–ω SST turbulence model to study the three dimensional flow and vortex structure about the half wing. The simulation shows that there is a strong relationship between the size of the tip vortex and the aerodynamic parameters such as lift, drag and pitching moment of the wing. The multi-tipped wing is the most effective at dispersing the vortice energy and reducing the induced drag. Optimization of the number of tips was found to be crucial to increase the lift coefficient while reducing the contributions of frictional and vortex drag. Although the lift was found to be increasing with the number of tips, the rise in frictional drag due to wetted surface area is a limiting factor towards aerodynamic efficiency. The results show that the multi-tip-4 is most capable at increasing the lift coefficient, but is surpassed by multi-tip-3 in lift to drag ratio. As aerodynamic efficiency is key for improving flight range and duration, it is concluded that multi-tip-3 is the optimum winglet for the given design conditions. The baseline wings show maximum performance at higher aspect ratios. Overall, winglets are found to be more effective at lower aspect ratio and provide highest improvement in aerodynamic efficiency at a moderate aspect ratio of 10.

Effects of tip cavity geometries on the aerothermal performance of the transonic turbine blade with cavity tip

The inevitable transonic tip leakage flow in unshrouded high pressure gas turbines induces aerodynamic loss and gives rise to heavy thermal loads on the blade tip. In the pursuit of superior gas turbine engine, cavity tips are widely used in high-pressure turbines to reduce the over-tip leakage flow. The present research aims to numerically investigate the influence of the depth of cavity and thickness of squealer rim on the aerothemal performance of the transonic turbine blade. Three-dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) equations with Spalart-Allmaras turbulence were solved to perform the simulation. The obtained results indicate that the variations of the cavity depth and squealer rim thickness have significant effects on the aerothermal performance of the transonic turbine blade tip regions. The phenomena in this transonic setup are different from the results obtained in subsonic condition. This study quantified that the improvement of aerodynamic efficiency contributed to the enhancement of heat flux on the blade tip in transonic condition by changing the geometry of tip cavity.

Extended Formation Flight at Transonic Speeds

Aircraft flown in formation can realize significant reductions in drag by flying in regions of wake upwash. However, most transports fly at transonic speeds where the impact of compressibility on formation flight is not well understood. This study uses an Euler solver to analyze the inviscid aerodynamic forces and moments of transonic wing/body configurations flying in a two-aircraft formation. Formations with large streamwise separation distances (10–50 wingspans) are considered. This work indicates that compressibility-related drag penalties in formation flight may be eliminated by slowing 2–3% below the nominal out-of-formation cruise Mach number, either at fixed lift coefficient or fixed altitude. The latter option has the additional benefit that the aerodynamic performance of the formation improves slightly at higher lift coefficients. Although optimal in-formation lift coefficients are not as high as those estimated by incompressible analyses, modest increases in altitude can yield further improvements in aerodynamic efficiency. Increasing the lateral separation of the aircraft allows for slightly higher cruise speeds in exchange for higher induced drag. For the configurations examined here, a 1–2% reduction in Mach number combined with a lateral spacing increase of 5% span (vertical spacing aligned with the vortex) achieves a total formation drag savings of about 10%.

Cell Geometry and Material Property Effects on Membrane and Flow Response

TO OPTIMIZE micro aerial vehicle (MAV) designs for size and speed regimes characteristic of small birds and insects, a growing subset of low-Reynolds-number research groups practice biomimetics to take advantage of nature-optimized designs proven effective within the MAV flight regime [1]. One common feature of many natural flyers is wing flexibility. Engineering models that mimic low-Reynolds-number fliers with fixed-wing flexibility have demonstrated improved aerodynamics compared with conventional rigid airfoils. This improvement is attributed to a combination of passive static and dynamic deformations of the flexible-membrane wings supported by semirigid, fixed-wing frames. Static deformation, of bothmembrane and frame, can advantageously affect airfoil camber and tip washout through inflation and alteration of aerodynamic and geometric twist [2–4]. Dynamic membrane deformations can improvemomentum transfer between the leeside free shear layer and recirculation region of models with rigid leading and trailing edges and a membrane attached in between, thereby, decreasing the extent of flow separation and corresponding wake size, as well as advantageously affecting the aerodynamic forces [5,6]. Similar vibrations also exist for membrane wings with an unattached trailing edge. Hubner and Hicks [7] showed aerodynamic efficiency improvement by scalloping the trailing edge and developed scaling trends with respect to cell geometry. Johnston et al. [8] demonstrated via high-speed imagery that membrane prestrain increased flutter onset velocity while reducing the magnitude of the postflutter limit cycle oscillations. A free trailing-edge wing structure typically includes a flat or cambered frame of moderate or low aspect ratio that is significantly less compliant than the attached membrane. The membrane is attached along the leading edge of the frame and along battens (or ribs) extending from the leading edge. In this Note, it is documented that the initial flutter onset frequency of zero-applied-pretension membranes originates from small-amplitude membrane vibrations at the natural frequency of the membrane. Although applied pretensioning will affect the frequency, cell geometry and material properties are shown to play an important role as well. Spectral data from the membrane and the leeside shear layer via simultaneously sampled hot-wire anemometry and laser vibrometry are presented and discussed in this Note.

Turbine Stator Well CFD Studies: Effects of Coolant Supply Geometry on Cavity Sealing Performance

The increase of aeroengine performance through the improvement of aerodynamic efficiency of core flow is becoming more and more difficult to achieve. However, there are still some devices that could be improved to enhance global engine efficiency. Particularly, investigations on the internal air cooling systems may lead to a reduction of cooling air with a direct benefit to the overall performance. At the same time, further investigations on heat transfer mechanisms within turbine cavities may help to optimize cooling air flows, saving engine life duration. This paper presents a computational fluid dynamics (CFD) study aimed at the characterization of the effects of different geometries for cooling air supply within turbine cavities on wall thermal effectiveness and sealing mass flow rate. Several sealing air supply geometries were considered in order to point out the role of cooling air injection position, swirl number, and jet penetration on the cavities’ sealing performance. Steady state calculations were performed using two different computational domains: the first consists of a sector model of the whole turbine including the second stator well, while the second is a cut-down model of the stator well. Thanks to the simplified geometry of the test rig with respect to actual engines, the study has pointed out clear design suggestions regarding the effects of geometry modification of cooling air supply systems.

Numerical Study of Heat Transfer Around the Small Scale Airfoil Using Various Turbulence Models

A numerical investigation of low-Reynolds number flows with thermal effect around the MAV airfoils using various turbulence models, including an algebraic Baldwin-Lomax model, Spalart-Allmaras one equation, and two equation (k-ω and SST-k-ω) turbulence models, is presented. First, the thermal effect on the aerodynamic efficiency is studied for flow around a rectangular MAV wing, based on the NACA0012 airfoil section at low-aspect ratio (AR = 2) and an angle of attack equal to 0°. Second, details of the thermal effect are limited to the two-dimensional NACA0012 airfoil with chord length of 3.81 cm. This study shows that the improvement of aerodynamic efficiency (increase lift and reduce drag) is achieved by the generation of a temperature difference between extrados and intrados of the airfoil (by cooling the upper surface and heating the lower surface). The numerical results obtained with various turbulence models are in good agreement with experiment data, except the k-ω turbulence model. These results are performed with the CFD-FASTRAN code, using the fully implicit scheme for time integration and the upwind Roe flux difference splitting scheme for space discretization augmented by a high order Osher-Chakravarthy limiter.