Induced Drag Research Articles

Direct numerical simulation of supersonic boundary layers over a microramp: effect of the Reynolds number

Microvortex generators are passive control devices smaller than the boundary layer thickness that energise the boundary layer to prevent flow separation with limited induced drag. In this work, we use direct numerical simulations (DNS) to investigate the effect of the Reynolds number in a supersonic turbulent boundary layer over a microramp vortex generator. Three friction Reynolds numbers are considered, up to $Re_\tau = 2000$ , for fixed free stream Mach number $M_\infty =2$ and fixed relative height of the ramp with respect to the boundary layer thickness. The high-fidelity data set sheds light on the instantaneous and highly three-dimensional organisation of both the wake and the shock waves induced by the microramp. The full access to the flow field provided by DNS allows us to develop a qualitative model of the near wake, explaining the internal convolution of the Kelvin–Helmholtz vortices around the low-momentum region behind the ramp. The overall analysis shows that numerical results agree excellently with recent experimental measurements in similar operating conditions and confirms that microramps effectively induce a significantly fuller boundary layer even far downstream of the ramp. Moreover, results highlight significant Reynolds number effects, which in general do not scale with the ramp height. Increasing Reynolds number leads to enhanced coherence of the typical vortical structures in the field, faster and stronger development of the momentum deficit region, increased upwash between the primary vortices from the sides of the ramp – and thus increased lift-up of the wake – and faster transfer of momentum towards the wall.

On the spurious effects in Lamb-vector-based force decomposition methods

Recent methods based on Lamb vector integration allow for a far-field formulation and decomposition of the whole aerodynamic force, with identification of local flow structures associated with the force generation. Different exact Lamb-vector-based force formulations were proposed in the past and the decomposition of total drag into lift-induced and parasite contributions was subject of very recent studies. However, inconsistencies were also reported, raising questions on the physical role of a non-zero induced drag found in two-dimensional flows. Moreover, the effect of the arbitrary pole (appearing in Lamb-vector-based formulas) on the numerical accuracy of such methods was never investigated. Additionally, the separation of parasite drag into viscous and wave drag contributions by Lamb vector field analysis is still questioned. In this paper, the accuracy of different force formulas and of the drag decomposition in lift-induced and parasite contributions is first analyzed, for steady flows. Two-dimensional numerical solutions around RAE2822 and NACA0012 airfoils are considered, the latter in both inviscid and viscous flows (at low and high Reynolds number), to analyze consistency between lift-induced/parasite drag definitions and the drag generated in isentropic flow conditions (reversible drag) or due to entropy production (irreversible drag). A spurious induced drag contribution (related to the streamwise momentum perturbation) is identified, resulting in negative induced drag values in two-dimensional flows. The effect of a shift in the pole location is also analysed, with reference to its impact on the total force and on drag decomposition accuracy, then a new approach to parasite drag breakdown into physical constituents (viscous and wave contributions) is proposed and results are compared against predictions obtained using consolidated thermodynamic-based methods and against available results from recent literature.

Novel UAS Propeller Design Part 1: Using an Unloaded Tip to Reduce Power Requirements and Lower Generated Sound Levels for Propellers Designed for Minimum Induced Drag

Abstract Today, over 500 eVTOL vehicles are being developed for everything from Urban Air Mobility to package delivery. In addition, Unmanned Aircraft Systems (UASs) are used in a variety of applications to include intelligence, surveillance, and reconnaissance (ISR) as well as resupply for the military. Most of these vehicles utilize electric propulsion systems with propellers. Efficient propellers with reduced noise generation are necessary for these vehicles to coexist in urban environments or be used for ISR missions. Traditional propeller design uses Blade Element Momentum Theory (BEMT) to minimize induced losses. The current investigation describes a novel propeller design approach that minimizes induced drag by reducing the thrust loading near tip. This reduces the tip vortex strength lowering the Sound Pressure Level (SPL) and power required. A parametric study of 18 propellers examined performance using traditional BEMT design near the hub and progressing to zero thrust loading at the tip. A microphone on a traverse mounted behind the propeller was used to measure the peak SPL and its location in a wind tunnel. The best performing unloaded tip propeller showed 5.2% reduction in power required and 12 dB SPL reduction compared to a commercial propeller at the same test conditions. Keywords: UAS propeller, propeller design, airfoil

Dynamic of Tunneled Planing Hulls in Waves

A tunneled planing craft is a high-speed boat with two tunnels over the hull bottom that are designed to improve the vessel’s performance. Hydrodynamic performance of tunneled planing hulls in calm-water is well-known, however, current information on wave conditions is limited. In this study, two different tunneled planing hulls with two degrees of freedom in heave and pitch motions are studied in regular waves by using the computational fluid dynamics (CFD) method based on the Unsteady Reynolds Averaged Navier-Stokes Equations (URANSE) in conjunction with k−ϵ turbulence model. The results demonstrate that tunneled planing hull motions in waves are nonlinear. In addition, it is found that the dynamic responses of heave and pitch motions as well as occurrence portability of the fly-over phenomenon significantly increases as the Froude number grows. Fly-over motions resulted in vertical motions and acceleration up to 5g, high impact pressure, and large induced drag. At a very high planing speed, after flying over the water surface, when the vessel re-enters the water, the resulting hydrodynamic load leads to a second fly-over motion. Since the fly-over is an unwanted movement with adverse effects, these results can provide a better understanding of the fly-over motion that one may consider in future design for improving the planing hull performance.

Correction to: Optimum Induced Drag of Wingtip Devices: The Concept of Best Winglet Design

Correction to: Optimum Induced Drag of Wingtip Devices: The Concept of Best Winglet Design

Preliminary Design of Integrated Partial Turboelectric Aircraft Propulsion Systems

This paper presents a novel tool for the modeling of partial turboelectric propulsion systems together with a corresponding case study for a commercial single-aisle aircraft. In order to reduce the environmental impact of air traffic, radically new aircraft and propulsion concepts with a high market penetration are needed. Partial turboelectric propulsion systems seem to offer a promising option to achieve this. For the development of these propulsion systems, a preliminary design tool with a homogeneous and sufficiently high fidelity, both for turbomachinery and electric components, is needed. To address this, the authors of this publication have developed a tool based on the GasTurb software. The models developed, in particular for the electric components which together form the electric powertrain, are described here. In the case study, which demonstrates the coupling of the developed tool with an aircraft design environment, a conventional turboprop baseline aircraft is compared to a derived aircraft which features a partial turboelectric propulsion system with wingtip propellers. The latter are intended to reduce the induced drag, enabling a reduction of the aircraft's total shaft power demand compared to the conventional baseline aircraft. The comparison between the partial turboelectric aircraft and the baseline aircraft indicates that fuel reduction increases with power split. However, primarily increasing electric powertrain masses and a stagnating drag reduction result in lower additional fuel reductions for higher power splits. Despite these conclusions, the predicted induced drag reductions need further refinement as they were found to be optimistic. In summary, this publication presents a methodology and a set of physics-based component models for the preliminary design of partial turboelectric propulsion systems, so that the electric components can be investigated and optimized at the same high level of detail as the gas turbine.

Prediction of Sand Production Through Porous Media: Mechanisms and Challenges to Optimising the Inefficiencies

One of the challenges facing drilling companies in the completion and production of oil and gas wells is sand production from the formation. The ability to predict sand production in the wells of a reservoir, to decide to use different methods of control is considered a fundamental issue. Therefore, analysis and study of sand production conditions and selecting the optimal drilling route before drilling wells are significant issues that are less considered. According to the findings of this study, due to the sand grains adhesion issue, saturation increase has caused to increase in the intermolecular uptake, and therefore moisture has been decreased. It leads to reduction in the sand production rate. Pressure increase has a direct relationship with the sand production rate due to increased induced drag forces. Moreover, phenol–formaldehyde resins provided an acceptable measurement as there are no significant changes in porosity and permeability.

An aerodynamic performance study and analysis of SD7037 fixed wing UAV airfoil

This work presents an investigation of aerodynamic characteristics of SD7037 low Reynolds number fixed win UAV airfoil. In this work the model design considerations of SD7037 low Reynolds number airfoil has been used to design and analysis. The model design parameters are consistent for the evaluation of aircraft performance and data are recomputed. The aircraft aerodynamic induced drag factor is selected as a parameter for design method and this has been approximately calculated for the airfoil and wing characteristic curves. The results gained by analysis from the designed airframe are suitable for the soft computing requirements. The calculated performance aspects came to be desirable and the soft computing techniques and feature detection program successfully differentiated between the runway and other objects to test automatic take off and landing of UAV. As planned the test for stability of the UAV was performed successfully and the model was self-stabilizing it-self.

Aerodynamical Optimization of Adaptable Span Wing of Telescopic Spar and Foldable Wing Tip using Computational Fluid Dynamics

The project aims to analyze aerodynamic coefficients of adaptable span wing, which increases the lift of the aircraft at various flight conditions by increasing the span of the wing and also decreases its span to adapt Group V airport gate, which is restricted to a maximum 65 m wingspan of aircraft. Present days there is no adaptable wing that changes its shape or its span. All the commercial airplane wings are only fixed wings. To increase more lift at the time of takeoff or landing, the pilot has to stay with the ailerons and flaps. But at the time of the cruise, flaps give more induced drag. Adaptable span wing paves a way to have a lift at any time with less induced drag. Airports are 6 types based on the maximum span of their gates. To increase the lift, it is easy to increase the span of a wing and to keep it fixed, but if the span is more than 65 m, it falls under the category of Group VI airports. These Group VI airports are less available, and Group V airports are mostly available worldwide. This project aims to increase the span beyond 65 m and also to accommodate in Group V airports. Methods of Telescopic spar expansion and foldable wingtip are used. For this work Boeing 777-300 ER Wing with its airfoil is taken as a reference. One side of the wing is taken for analysis, and the models have made in CATIA V5 of various length from its original half span 29.3m to 34.3m by increasing one by one metre. Also, with foldable wingtip span is increased at its unfolded state with 2m. Each and every model is analyzed with a variable angle of attack, and lift curves were obtained. These curves help us to determine the optimized span of the adaptable wing.

Review of Structural Issues in the Design of a Box Wing Aircraft

As part of the search for the next future airliner configuration, and to mitigate the negative impact of air travels on the environment, there have been renewed interests in the aircraft design of unconventional configurations such as the Blended Wing Body and Joined Wing aircraft concepts. The Joined/Box-Wing aircraft configuration attracted the attention of researchers due to its claimed merits of reduced structural weight and low induced drag.

An analysis on Aerodynamics Performance Simulation of NACA 23018 Airfoil Wings on Cant Angles

Winglet attached on the tip of aircraft wings to increase lift. Mainly, winglet used for increasing aerodynamic efficiency, it decreases induced drag caused by vortex on wings tip. The phenomenon of vortex is collision of high-pressured air below the wings meet the low-pressured air above it that cause turbulence. Induced drag may reach 40% of total drag during cruising, and 80-90% while take off. A procedure to decrease induced drag is using wing tip devices. It used on commercial aircrafts and the most frequently used is blended winglet. Numerical study conducted to examine the best aerodynamic performance of sub-sonic plane wings in angles of attack. Analysis on NACA 23018 airfoil wings with blended winglet on the tip was conducted. Freestream velocity of 40 m/s or Re = 1 × 106, and angle of attack (α) 0o, 5o, 10o, and 15o are used. Evaluation for parameter includes coefficient pressure (Cp), velocity profile, lift, drag, and ratio CL/CD. Obtained contour are pressure contour, velocity, and vorticity. In view of all this, there is increasing performance of aerodynamic with CL/CD ratio of wings with blended winglet and plain wing. Reaching current angle of attack, the function of winglet is gradually decrease.

Minimum Induced Drag Theorems for Multiwing Systems

Under the assumption of a rigid wake aligned with the freestream velocity, a computationally efficient induced drag minimization procedure, tailored for the preliminary design phases of generic multiwing systems, is presented. The method is based on a variational approach, which leads to the formulation of a system of coupled integral equations in the unknown circulation distributions. It is shown that the augmented Munk’s minimum induced drag theorem has general validity for any given number and types of wings. Under optimal conditions, the aerodynamic efficiency of each wing is shown to coincide with the aerodynamic efficiency of the entire system, regardless of the number of wings and their shapes/wingspans; moreover, the aerodynamic load on each wing cannot be negative. In the past, it was demonstrated that changing the sign of curvature did not affect the optimal circulation and minimum induced drag for single nonplanar wings. This has been proven to be a far more general theorem in which, given an arbitrary number of generic nonplanar wings, the optimal circulations, load repartitions, and induced drag do not change if all lifting lines are replaced with mirrored (with respect to the horizontal plane) counterparts. It has also been verified that any wing system internal to a closed wing should be unloaded under optimal conditions, demonstrating that, if canard/tail are added to Box Wings, these additional lifting surfaces should be placed outside the region identified by the closed wing to avoid penalty on the induced drag. Several other properties of multiwings are presented, with emphasis on the relationship between closed and open systems conceptually filling the space identified by the closed wing. Results present several multiwing systems including nonplanar wings and closed systems. It is verified that the optimal conditions of a closed system part of a more complex multiwing can be studied as a limit case of a C-wing whose tips are brought close to each other or as a limit case of a biwing, confirming the generality of previous findings. The classical straight lifting line has been observed to have the minimum optimal aerodynamic efficiency, in terms of induced drag, for a given wingspan and lift if compared to any optimally loaded generic nonplanar open or closed systems.

Flexible Wing of HALE UAV using Two-way Fluid Structure Interaction Method

Simulation of High Altitude Long Endurance (HALE) UAV wing using two-way fluid structure interaction (FSI) method is presented. To achieve its mission, the HALE wing was designed to have high aspect ratio. With longer wing span, the HALE UAV may produce less induced drag and lift-loss which caused by the decrease in wingtip vortex strength. However, the wing structure with longer span becomes more elastic that may yield large deformation when aerodynamic loads applied. This deformation influences flow characteristics at the surrounding of the wing causing the change of aerodynamic loads distribution on the wing. Subsequently, this new load provides a new deformation to the wing structure and vice versa. This interaction in a couple process called as fluid structure interaction (FSI) of the HALE wing was simulated using ANSYS 15.0 software. The unsteadiness and viscous flows at low speed are evaluated using the solution of time-dependent Reynolds Averaged Navier-Stokes (RANS) with SST k-ω turbulent model. In addition, multi-block structured grids are generated to provide more accurate viscous result and to anticipate negative volume of the mesh which may occur due to the wing deformation during simulation. Five different simulations with variation of material characteristics including Young’s modulus and Poisson’s ratio are carried out. The results include global aerodynamic characteristics at various material characteristics.

Mathematical model for takeoff simulation of a wing in proximity to the ground

Aircraft flying close to the ground benefit from enhanced efficiency owing to decreased induced drag and increased lift. In this study, a mathematical model is developed to simulate the takeoff of a wing near the ground using an Iterative Boundary Element Method (IBEM) and the finite difference scheme. Two stand-alone sub-codes and a mother code, which enables communication between the sub-codes, are developed to solve for the self-excitation of the Wing-In-Ground (WIG) effect. The aerodynamic force exerted on the wing is calculated by the first sub-code using the IBEM, and the vertical displacement of the wing is calculated by the second sub-code using the finite difference scheme. The mother code commands the two sub-codes and can solve for the aerodynamics of the wing and operating height within seconds. The developed code system is used to solve for the force, velocity, and displacement of an NACA6409 wing at a 4° Angle of Attack (AoA) which has various numerical and experimental studies in the literature. The effects of thickness and AoA are then investigated and conclusions were drawn with respect to generated results. The proposed model provides a practical method for understanding the flight dynamics and it is specifically beneficial at the pre-design stages of a WIG effect craft.

유선형 고속주행 버스의 공력특성에 관한 실험 연구

Abstract : In this study, a wind tunnel test was conducted to measure the aerodynamic characteristics of a streamline- designed high-speed bus with the change of wind direction and speed and the result is compared with the aerodynamic performance of a commercialized high-speed bus model (Model-0) manufactured by Zyle Daewoo Bus Corp. Aero-dynamic performance of the existing rear-spoiler was tested to prove its aerodynamic effect on the test model bus. From the study, it was found that 24.6 % of the total drag of the original bus model (Model-0) was reduced on the streamline- designed model bus(model-1) without the rear-spoiler but only 14.3 % of the total drag was reduced with the spoiler on the streamlined model bus. It means that the rear spoiler does not work properly with the streamlined model bus (model-1) and should be noted that an optimum design of a rear-spoiler of a vehicle is important to reduce the induced pressure drag and increase the driving stability of a vehicle against yaw motion. The experimental outcome was also compared to the previous numerical research result to evaluate the reliability of the numerical algorithm of the aerodynamic performance analysis of a vehicle. The error rate (%) of the numerical result to the experimental output is about 5.4 % and it is due to the simplified body configuration of the numerical model bus. The drag increases at the higher yaw angle because the transparent frontal area of the model vehicle increases and the downward force increases with the yaw angle as well. It has a positive effect to the driving stability of the vehicle but the moderated downward force should be kept for the fuel economy of a vehicle.

Qualitative skeletal correlates of wing shape in extant birds (Aves: Neoaves).

BackgroundAmong living fliers (birds, bats, and insects), birds display relatively high aspect ratios, a dimensionless shape variable that distinguishes long and narrow vs. short and broad wings. Increasing aspect ratio results in a functional tradeoff between low induced drag (efficient cruise) and increased wing inertia (difficult takeoff). Given the wide scope of its functional effects, the pattern of aspect ratio evolution is an important factor that contributes to the substantial ecological and phylogenetic diversity of living birds. However, because the feathers that define the wingtip (and hence wingspan and aspect ratio) often do not fossilize, resolution in the pattern of avian wing shape evolution is obscured by missing information. Here I use a comparative approach to investigate the relationship between skeletal proxies of flight feather attachment and wing shape.ResultsAn accessory lobe of the internal index process of digit II-1, a bony correlate of distal primary attachment, shows weak but statistically significant relationships to aspect ratio and mass independent of other skeletal morphology. The dorsal phalangeal fossae of digit II-1, which house distal primaries VIII and IX, also show a trend of increased prominence with higher aspect ratio. Quill knobs on the ulna are examined concurrently, but do not show consistent signal with respect to wing shape.ConclusionsAlthough quill knobs are cited as skeletal correlates of flight performance in birds, their relationship to wing shape is inconsistent among extant taxa, and may reflect diverging selection pressures acting on a conserved architecture. In contrast, correlates of distal primary feather attachment on the major digit show convergent responses to increasing aspect ratio. In light of the diversity of musculoskeletal and integumentary mophology that underlies wing shape in different avian clades, it is unlikely that a single skeletal feature will show consistent predictive power across Neoaves. Confident inference of wing shape in basal ornithurine birds will require multiple lines of evidence, together with an understanding of clade-specific evolutionary trends within the crown.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0303-7) contains supplementary material, which is available to authorized users.

Invariant Formulation for the Minimum Induced Drag Conditions of Nonplanar Wing Systems

Under the hypotheses of linear potential flow and rigid wake aligned with the freestream, a configuration-invariant analytical formulation for the induced drag minimization of single-wing nonplanar systems is presented. Following a variational approach, the resulting Euler–Lagrange integral equation in the unknown circulation distribution is obtained. The kernel presents a singularity of the first order, and an efficient computational method, ideal for the early conceptual phases of the design, is proposed. Munk’s theorem on the normalwash and its relation with the geometry of the wing under optimal conditions is naturally obtained with the present method. Moreover, Munk’s constant of proportionality, not provided in his original work, is demonstrated to be the ratio between the freestream velocity and the optimal aerodynamic efficiency. The augmented Munk’s minimum induced drag theorem is then formulated. Additional induced drag theorems are demonstrated following the derivations of this invariant procedure. Several nonplanar wing systems are proposed and analyzed, and the optimal induced drag and circulation are provided. The conjecture regarding the equality of the optimum induced drag of a quasi-closed C-wing with the induced drag of the corresponding closed system is also verified for several configurations including the box wing.

Far-Field Induced Drag Prediction Using Vorticity Confinement Technique

The goal of this study is to show the efficiency of the wake-integral technique coupled with vorticity confinement method for the prediction of induced drag by inviscid numerical modeling. While the vorticity confinement method has previously been used to capture trailing vortices, its quantitative effect on improving wake-integral drag predictions has not been investigated. In the present study, parameters of vorticity confinement are tuned and the advantages of using a variable confinement parameter are demonstrated. A combination of vorticity confinement with the wake-integral technique indicates that the computational fluid dynamics-predicted induced drag for wing with and without winglet becomes insensitive to wake-integration plane location, the computed drag approaches its theoretical lifting-line value, and the spurious entropy drag is suppressed.

Multi-fidelity design optimization of transonic airfoils using shape-preserving response prediction

A computationally efficient methodology for transonic airfoil design optimization is presented. Our approach exploits a corrected physics-based low-fidelity surrogate that replaces, in the optimization process, an accurate but computationally expensive highfidelity airfoil model. Correction of the low-fidelity model is achieved by aligning its corresponding airfoil surface pressure distributions with that of the high-fidelity model using a shape-preserving response prediction technique. The presented method is applied to airfoil lift maximization in two-dimensional inviscid transonic flow, subject to constraints on shock induced pressure drag and airfoil cross-sectional area. More than a 90% reduction in high-fidelity function calls is achieved when compared to direct highfidelity model optimization.

Aeroelastic tailoring using lamination parameters

The aim of the present work is to passively reduce the induced drag of the rear wing of a Formula One car at high velocity through aeroelastic tailoring. The angle-of-attack of the rear wing is fixed and is determined by the required downforce needed to get around a turn. As a result, at higher velocity, the amount of downforce and related induced drag increases. The maximum speed on a straight part is thus reduced due to the increase in induced drag. A fibre reinforced composite torsion box with extension-shear coupled upper and lower skins is used leading to bending-torsion coupling. Three-dimensional static aeroelastic analysis is performed loosely coupling the Finite Element code Nastran and the Computational Fluid Dynamics panel code VSAERO using ModelCenter. A wing representative of Formula One rear wings is optimised for minimum induced drag using a response surface methodology. Results indicate that a substantial induced drag reduction is achievable while maintaining the desired downforce during low speed turns.