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Showing papers on "Vortex lattice method published in 2016"


Journal ArticleDOI
TL;DR: In this article, a non-linear formulation of the classical Vortex Lattice Method (VLM) approach for calculating the aerodynamic properties of lifting surfaces is presented. But the method is not suitable for the analysis of a single aircraft.

56 citations


Journal ArticleDOI
TL;DR: In this article, an aeroservoelastic modeling approach is presented to investigate dynamic load alleviation in large wind turbines with composite blades and trailing-edge aerodynamic surfaces, where the tower and rotating blades are modeled using geometrically non-linear composite beams and linearized about reference rotating conditions with potentially arbitrarily large structural displacements.
Abstract: This paper presents an aeroservoelastic modeling approach to investigate dynamic load alleviation in large wind turbines with composite blades and trailing-edge aerodynamic surfaces. The tower and rotating blades are modeled using geometrically non-linear composite beams and linearized about reference rotating conditions with potentially arbitrarily large structural displacements. The aerodynamics of the rotor are represented using a linearized unsteady vortex lattice method, and the resulting aeroelastic system is written in a state-space description that is both convenient for model reductions and control design. A linear model of a single blade is then used to design an ℋ∞ regulator, capable of providing load reductions of up to 13% in closed loop on the full wind turbine non-linear aeroelastic model. When combined with passive load alleviation through aeroelastic tailoring, dynamic loads can be further reduced to 35%. While the separate use of active flap controls and passive mechanisms for load alleviation has been well-studied, an integrated approach involving the two mechanisms has yet to be fully explored and is the focus of this paper. Finally, the possibility of exploiting torsional stiffness for active load alleviation on turbine blades is also considered. Copyright © 2014 John Wiley & Sons, Ltd.

42 citations


Journal ArticleDOI
TL;DR: In this article, an extended unsteady vortex-lattice method is developed to study the aerodynamics of insect flapping wings while hovering and during forward flight, and a convergence analysis is carried out to derive an optimal aerodynamic mesh and a time-step size for flapping-wing models.
Abstract: An extended unsteady vortex-lattice method is developed to study the aerodynamics of insect flapping wings while hovering and during forward flight. Leading-edge suction analogy and vortex-core growth models are used as an extension, which is incorporated into a conventional unsteady vortex-lattice method in an effort to overcome the challenges that arise when simulating insect aerodynamics such as wing–wake interaction and leading-edge effects. A convergence analysis was carried out to derive an optimal aerodynamic mesh and a time-step size for flapping-wing models. A parallel computing technique was used to reduce computational time. The aerodynamics of hawkmoth (Manduca sexta) wing models was simulated, and the results were validated against previous numerical and experimental data.

42 citations


Journal ArticleDOI
TL;DR: In this article, a quasi-three-dimensional aerodynamic solver is developed and connected to a finite beam element model for wing aerostructural optimization, which needs much lower computational costs, while computes the wing drag and structural deformation with a level of accuracy comparable to the higher fidelity CFD and FEM tools.
Abstract: This paper presents a method for wing aerostructural analysis and optimization, which needs much lower computational costs, while computes the wing drag and structural deformation with a level of accuracy comparable to the higher fidelity CFD and FEM tools. A quasi-three-dimensional aerodynamic solver is developed and connected to a finite beam element model for wing aerostructural optimization. In a quasi-three-dimensional approach an inviscid incompressible vortex lattice method is coupled with a viscous compressible airfoil analysis code for drag prediction of a three dimensional wing. The accuracy of the proposed method for wing drag prediction is validated by comparing its results with the results of a higher fidelity CFD analysis. The wing structural deformation as well as the stress distribution in the wingbox structure is computed using a finite beam element model. The Newton method is used to solve the coupled system. The sensitivities of the outputs, for example the wing drag, with respect to the inputs, for example the wing geometry, is computed by a combined use of the coupled adjoint method, automatic differentiation and the chain rule of differentiation. A gradient based optimization is performed using the proposed tool for minimizing the fuel weight of an A320 class aircraft. The optimization resulted in more than 10 % reduction in the aircraft fuel weight by optimizing the wing planform and airfoils shape as well as the wing internal structure.

40 citations


Journal ArticleDOI
TL;DR: In this paper, an integrated approach for flexible-aircraft time-domain aeroelastic simulation and controller design suitable for wake encounter situations is presented, where the aerodynamics are modeled using the unsteady vortex lattice method and include the arbitrary timedomain downwash distributions of a wake encounter.
Abstract: This paper introduces an integrated approach for flexible-aircraft time-domain aeroelastic simulation and controller design suitable for wake encounter situations. The dynamic response of the vehicle, which may be subject to large wing deformations in trimmed flight, is described by a geometrically nonlinear finite-element model. The aerodynamics are modeled using the unsteady vortex lattice method and include the arbitrary time-domain downwash distributions of a wake encounter. A consistent linearization in the structural degrees of freedom enables the use of balancing methods to reduce the problem size while retaining the nonlinear terms in the rigid-body equations. Numerical studies on a high-altitude, long-endurance aircraft demonstrate the reduced-order modeling approach for load calculations in wake vortex encounters over a large parameter space. Closed-loop results finally explore the potential of combining feedforward/feedback H∞ control and distributed control surfaces to obtain significant load ...

27 citations


Journal ArticleDOI
TL;DR: The present note introduces the ongoing development of the Java Program Toolchain for Aircraft Design (JPAD), a Java-based desktop application for aircraft designers to provide a library and a set of companion tools based onmodern software technology as a support for typical preliminary design studies.
Abstract: T HEconceptual and preliminary design phases play a very important role for the development of the future transport aircraft. A computational framework capable of finding an optimal configuration satisfying several basic requirements would be an essential tool for industrial aircraft designers. Such software should be developed around all those basic principles and approaches to aircraft preliminary design well described in several textbooks on the subject [1–9]. Amodern preliminary aircraft design tool should be characterized by a certain level of accuracy and reliability (albeit using fast and simple semiempirical procedures), the capability to perform multidisciplinary analyses, and reasonably short computational times. Because of the particular relevance of production costs, noise, emissions,maintenance, andoperative costs in the commercial success of a transport aircraft, amodern software framework should be developedwith amultidisciplinary optimization (MDO) approach inmind.Another important aspect is the user-friendliness of the interface that should allow the user to interact with the design framework in an easy, fast, and efficient way. Of the same or even of more importance is the possibility to include in the software multiple fidelity analysis methods or to modify and develop new semi-empirical models to achieve better accuracy. It should also be possible to export the aircraft configuration geometry (e.g., as a CADmodel or a surface mesh) in one or more standard formats and to execute high-fidelity analyseswith external tools (e.g., computational fluid dynamics or Finite ElementMethod (FEM) solvers). Many aircraft design computational tools have been developed by several universities, companies, aeronautical industries, and research centers in the past and recent years [10–17]. In many recent papers [18–21], the importance of including a knowledge-based engineering approach in modern aircraft design tools is highlighted. The present note introduces the ongoing development of the Java Program Toolchain for Aircraft Design (JPAD), a Java-based desktop application for aircraft designers. The aim of JPAD, which eventually will be released as open-source software, is to provide a library and a set of companion tools based onmodern software technology as a support for typical preliminary design studies. The software has been conceived to be used in an industrial environment across conceptual and preliminary design phases. In these phases, a lot of different configurations have to be considered, and so the proposed software relies mostly on semi-empirical analysis methods and is capable to quickly provide results. A comprehensive study of the methods available in the literature has been first carried out to improve the accuracy of the results; each method has been tested against experimental data (produced in house or drawn from literature) so that statistical quantities (e.g., standard deviation) could be estimated either to find the best method currently available or to make a merger of different methods. The use of middleand high-fidelity methods (e.g., in aerodynamics, numerical lifting line, vortex lattice method, or computational fluid dynamics) is beneficial in preliminary studies, provided that their computational time is reasonably short. In this respect, the development of new semi-empirical methodologies or improved analysis approaches (especially for innovative aircraft configuration) is an important item that has been extensively reported in several recent works [21–26]. The aircraft design research group at the University of Naples has matured in the past two decades experience in design of light and turboprop transport aircraft [27,28]. Recent aircraft design activities carried out by the authors on a commuter 11-seat aircraft has been described and illustrated in some recent papers [29,30]. The matured know-how in aircraft aerodynamic designs has also found confirm through specific flight-testing research [31,32].

26 citations


Journal Article
13 Jun 2016-Aviation
TL;DR: In this article, the authors presented an approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft.
Abstract: The need to rapidly scan large design spaces during conceptual design calls for computationally inexpensive tools such as the vortex lattice method (VLM). Although some VLM tools, such as Vorview have been extended to model fully-supersonic flow, VLM solutions are typically limited to inviscid, subcritical flow regimes. Many transport aircraft operate at transonic speeds, which limits the applicability of VLM for such applications. This paper presents a novel approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft. The approach is extended to predict flow separation and capture the attenuation of aerodynamic forces due to boundary layer viscosity by coupling the TSD solver with an integral boundary layer (IBL) model. The modeling framework is applied to the NASA General Transport Model (GTM) integrated with a novel control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF).

23 citations


Proceedings ArticleDOI
13 Jun 2016
TL;DR: In this article, the authors presented an approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft.
Abstract: The need to rapidly scan large design spaces during conceptual design calls for computationally inexpensive tools such as the vortex lattice method (VLM). Although some VLM tools, such as Vorview have been extended to model fully-supersonic flow, VLM solutions are typically limited to inviscid, subcritical flow regimes. Many transport aircraft operate at transonic speeds, which limits the applicability of VLM for such applications. This paper presents a novel approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft. The approach is extended to predict flow separation and capture the attenuation of aerodynamic forces due to boundary layer viscosity by coupling the TSD solver with an integral boundary layer (IBL) model. The modeling framework is applied to the NASA General Transport Model (GTM) integrated with a novel control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF).

22 citations


Journal ArticleDOI
TL;DR: In this article, a framework for the geometrically nonlinear aeroelastic stability analysis of very flexible wings is constructed to illustrate the unique aero-elastic characteristics and convenient use of these designs in engineering analysis.
Abstract: VFAs (very flexible aircraft) have begun to attract significant attention because of their good flight performances and significant application potentials; however, they also bring some challenges to researchers due to their unusual lightweight designs and large elastic deformations. A framework for the geometrically nonlinear aeroelastic stability analysis of very flexible wings is constructed in this paper to illustrate the unique aeroelastic characteristics and convenient use of these designs in engineering analysis. The nonlinear aeroelastic analysis model includes the geometrically nonlinear structure finite elements and steady and unsteady nonplanar aerodynamic computations (i.e., the nonplanar vortex lattice method and nonplanar doublet-lattice method). Fully nonlinear methods are used to analyse static aeroelastic features, and linearized structural dynamic equations are established at the structural nonlinear equilibrium state to estimate the stability of the system through the quasimode of the stressed and deformed structure. The exact flutter boundary is searched via an iterative procedure. A wind tunnel test is conducted to validate this theoretical analysis framework, and reasonable agreement is obtained. Both the analysis and test results indicate that the geometric nonlinearity of very flexible wings presents significantly different aeroelastic characteristics under different load cases with large deformations.

16 citations


Journal ArticleDOI
TL;DR: In this article, a cropped delta wing with an external store using numerical and experimental methods in a subsonic and incompressible flight regime has been investigated, and the effects of different parameters such as wing thickness, wing aspect ratio, spanwise store position, store mass, aerodynamics of the store, underwing clearance and store center of gravity on both flutter speed and instability boundary of the wing are studied both analytically and experimentally.
Abstract: The present paper aims to investigate flutter phenomenon for cropped delta wing with an external store using numerical and experimental methods in a subsonic and incompressible flight regime. Wing structure is modeled based on von Karman plate theory. The unsteady vortex lattice method is applied to wing aerodynamic model and a slender-body theory is used for store aerodynamic model. The experimental tests have been conducted in an incompressible subsonic wind tunnel. The comparison indicates a satisfactory agreement between the experimental results and the theoretical analyses. Moreover, the effects of different parameters such as wing thickness, wing aspect ratio, spanwise store position, store mass, the aerodynamics of the store, underwing clearance and store center of gravity on both flutter speed and instability boundary of the wing are studied both analytically and experimentally. Also, the system behaviors and the oscillation amplitude are examined experimentally for post-flutter where time history simulation and phase portrait are obtained for various velocities. The FFT analysis of time history measured data shows that beside the dominant harmonic frequency, both superharmonic and subharmonic frequencies are clearly identifiable. The results obtained from experimental bifurcation diagram indicate the presence of hysteresis loop regions corresponding to the stable LCOs.

11 citations


Proceedings ArticleDOI
13 Jun 2016
TL;DR: This paper presents the novel nonlinear formulation of the Vortex Lattice Method approach for calculating the aerodynamic properties of lifting surfaces, constructed by using two-dimensional viscous analyses of the wing span-wise sections according to strip theory.
Abstract: This paper presents the novel nonlinear formulation of the Vortex Lattice Method approach for calculating the aerodynamic properties of lifting surfaces. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional

Journal ArticleDOI
Nicolas Aubin1, Benoit Augier1, Patrick Bot1, Frédéric Hauville1, Ronan Floch 
TL;DR: In this paper, a full-scale experimental study of a yacht rig and sails in real upwind sailing conditions and a comparison with Fluid Structure Interaction (FSI) simulations with the ARAVANTI model is presented.

01 Jan 2016
TL;DR: In this article, the hydrodynamic design of a pre-swirl stator with radially variable pitch, paired with a conventional propeller, is described, and the aim is to achieve the highest possible efficiency in various operating conditions, and to avoid efficiency penalties in off-design operation.
Abstract: Over the last two decades, an increasing number of studies have been conducted to develop and improve energy saving devices (ESDs) in order to increase the propulsive efficiency. One well-known example is the pre-swirl stator (PSS), which consists of an often asymmetric arrangement of fixed stator blades ahead of the propeller. This paper describes the hydrodynamic design of a pre-swirl stator with radially variable pitch, paired with a conventional propeller. The aim is to achieve the highest possible efficiency in various operating conditions, and to avoid efficiency penalties in off-design operation. To investigate the propeller and stator designs and configurations in different operating conditions, the computationally inexpensive vortex-lattice method is used as a first step to optimize the geometry in an initial parameter study. Then the flow over hull, stator and propeller is simulated in a CFD-based approach to confirm the results obtained in the first stage.

Journal ArticleDOI
TL;DR: In this paper, a new numerical approach based on the Vortex Lattice Method (VLM) for the solution of the hydrodynamic performances of cambered hulls in steady planing is formulated and validated.
Abstract: A new numerical approach based on the Vortex Lattice Method (VLM) for the solution of the hydrodynamic performances of cambered hulls in steady planing is formulated and validated. Due to its fully 3D formulation, the method can be applied to both cambered and un-cambered dihedral planing surfaces of any shape without any further approximation. The exact three-dimensional wetted surface of the hull is where the body boundary condition is fulfilled. The sprays region detaching both in front of the stagnation root line and from the wet portion of the chine are modeled in the numerical scheme by means of additional vortex lattice regions. The dynamic boundary condition at the stern of the hull is non-linear with respect to the perturbation potential. Results show the dynamic pressure consistently accounts for the 3D features of the flow especially in the case of cambered planing surfaces. The numerical method is verified by a systematic analysis against semi-empirical methods and it is finally validated with experimental results on prismatic as well as cambered dihedral planing surfaces. Excellent correlations are found for both types of planing surfaces that range in the same confidence interval of higher fidelity numerical models, such as RANSE solvers.

Journal ArticleDOI
26 Aug 2016
TL;DR: In this article, the aerodynamic performance of an existing HPA was evaluated using both the vortex lattice method and computational fluid dynamics, and a new HPA capable of winning the Kremer International Marathon Competition was designed and optimized.
Abstract: The special type of aircrafts in which the human power of the pilot is sufficient to take off and sustain flight are known as Human-Powered Aircrafts (HPAs). To explore the peculiarities of these aircrafts, the aerodynamic performance of an existing design is evaluated first, using both the vortex lattice method and computational fluid dynamics. In a second step, it is attempted to design and optimize a new HPA capable of winning the Kremer International Marathon Competition. The design will be special in that it allows one to include a second pilot on board the aircraft. As the structural deflection of the wing is found to be a key aspect during design, fluid–structure interaction simulations are performed and included in the optimization procedure. To assess the feasibility of winning the competition, the physical performance of candidate pilots is measured and compared with the predicted required power.

Proceedings ArticleDOI
04 Jan 2016
TL;DR: The single shooting method is used to identify optimal manoeuvres in the lateral dynamics of partially-supported wings of very low stiffness and to provide satisfactory results, not only when refining a predetermined actuation law but also when designing it from zero.
Abstract: The single shooting method is used identify optimal manoeuvres in the lateral dynamics of partially-supported wings of very low stiffness. The aim is to identify actuation strategies in the design of aircraft manoeuvres in which large wing deflections can substantially modify the vehicle structural and aerodynamic features. Preliminary studies are presented for a representative high-altitude long-endurance aircraft wing in hinged configuration. Nonlinear effects due to large deflections are captured coupling a geometrically exact beam model with an unsteady vortex lattice method for the aerodynamics. The optimal control problem is solved via a gradient-based algorithm. When lowering the wing stiffness, the nonlinearities connected to the system — such as the fore-shortening effect due to large bending deflections — increase the wing lateral stability but at the same time they also reduce aileron authority. The single-shooting optimisation is shown to capture these features and to provide satisfactory results, not only when refining a predetermined actuation law but also when designing it from zero.

Proceedings ArticleDOI
13 Jun 2016
TL;DR: In this article, a method is developed to approximate the root aerofoil design to achieve straight isobars on a wing of any given shape, within computational times that are suitable for conceptual design.
Abstract: For modern transonic transport aeroplanes, it is important to produce low drag at high cruise speeds. The root effect, caused by effects of symmetry on swept wings, decreases the performance of these aeroplanes. During aeroplane design, root modifications are applied to counteract this decrease in performance. Most conceptual aeroplane design tools do not have a method for design of the root aerofoil. However, the design of the root aerofoil has a significant influence on the properties of the final design, since it transfers the loads from the wing to the fuselage. Therefore, having a conceptual method for design of the wing root aerofoil will increase the accuracy of a conceptual aeroplane design. For conceptual design, computational times are important, to allow the designer to try different approaches and get a feel for the design. In this report a method is developed to approximate the root aerofoil design to achieve straight isobars on a wing of any given shape, within computational times that are suitable for conceptual design. First a method is developed for estimating the pressure distribution over the root aerofoil of a given wing. This is done by combining a method for estimation of the root effect due to thickness, a method for estimation of the root effect due to lift, a Vortex Lattice Method (VLM) and a two-dimensional panel method. A full potential method, MATRICS-V, is used to verify the results of the method, because of its proven validity. It is shown that the results of the first part of the method are generally in good agreement with results found by MATRICS-V. The effects of wing sweep, wing taper and addition of a wing kink can be modelled with results that are in good agreement with the verification data. For aft swept wings with positive lift, the pressure near the leading edge is underestimated. For forward swept wings with positive lift, the pressure on the upper surface is overestimated. For wings with a cambered aerofoil an inaccuracy occurs over the forward part of the profile. The general shape of the curve, however, is captured. Secondly, this method is coupled with an optimisation method for the root aerofoil, using Class-Shape function Transformation (CST) parametrisation. The target of the optimisation is set to achieve a similar pressure distribution over the wing root aerofoil as the pressure distribution over the outboard section of the wing. For the developed method, it is difficult to show that the results are valid, since there is no method that has a one-to-one match with the method developed. Therefore, the results are compared to the general characteristics observed in actual root aerofoil designs. The method shows the characteristic behaviour in terms of change in camber, change in location of maximumthickness and change in incidence angle. The increase in thickness, however, is not present. This is caused by the fact that the lower surface pressure distribution is also set as a target. In actual aeroplane design the lower surface is of less importance. In the method developed, however, it is of importance to retain the shape of specific aerofoil designs, like supercritical aerofoils, during optimisation. As a final verification, an optimised root aerofoil design is analysed using MATRICS-V. The results show that the root section pressure distribution is in good agreement with the outboard pressure distribution. In terms of computational time, the method is shown to generally produce reliable results within 30 seconds.

22 Jan 2016
TL;DR: In this paper, a prediction method for the propeller slipstream effect on the longitudinal stability and control of conventional aircraft configurations in the Initiator was developed and validated using wind tunnel data for the Fokker 50 and a special Saab 340 with T-tail configuration.
Abstract: As the aviation industry continues to strive for improvements in fuel efficiency throughout the entire aircraft design, interest has been renewed in propeller engines. New research into advanced turboprop engines, so-called open rotor engines, seems promising as they combine the inherent high propulsive efficiency of ordinary turboprop engines, with the capability of delivering higher thrust. Unfortunately, the implementation of propeller engines does have significant implications on the stability and controllability of an aircraft. These implications are primarily caused by the propeller slipstream, the complex streamtube behind the propeller with strong gradients in various flow quantities both in streamwise and radial direction. The objective of this thesis was to develop, implement, and validate a prediction method for the propeller slipstream effect on the longitudinal stability and control of conventional aircraft configurations in the Initiator. During the investigation of the propeller slipstream effect, an existing prediction method was found which was based on calculating the four major effects caused by the propeller slipstream on the longitudinal stability and control. These four effects are, an additional normal force at the propeller disk, an increase in lift over the wing due to the slipstream, a change in the tail-off pitching moment, and a change in tail contribution to the pitching moment due to increased downwash and dynamic pressure. This method seemed ideal as it not only gives relatively accurate results, but does so with computationaly inexpensive calculations. During the implementation of this method in the Initiator, additional changes were made to calculate aerodynamic variables which were previously estimated using an extended vortex lattice method program. This implemented prediction method was validated using the only available wind tunnel data for the Fokker 50 and a special Saab 340 with T-tail configuration. Through this validation, the prediction method proved to maintain an acceptable accuracy for all configurations with minimal computation time. Further analysis of the results showed that the propeller slipstream effect reduces the tail effectiveness due to an increase in downwash angle at the tail. This was especially the case for the Fokker 50, which due to its low wing configuration, has a further increase in downwash caused by an inflow effect of the outer flow into the streamtube.


Journal ArticleDOI
TL;DR: In this paper, the authors proposed to control the flow by inserting leading-edge and cross-flow slots and analysing the viscous flow development over the outer panels of a flying-wing configuration to maximise the performance of the vehicle's control surfaces.
Abstract: The objectives of the present study on Unmanned Combat Air Vehicles (UCAVs) are two-fold: first to control the flow by inserting leading-edge and cross-flow slots and analysing the viscous flow development over the outer panels of a flying-wing configuration to maximise the performance of the elevons control surfaces; second to predict high-lift performance particularly the maximum-lift characteristics. This is demonstrated using a variety of inviscid Vortex Lattice Method (VLM) and Euler, and viscous CFD Reynolds Averaged Navier-Stokes (RANS) methods. The computational results are validated against experiment measured in a wind tunnel. Two flying-wing planforms are considered based around a generic 40 edge-aligned configuration. The VLM predicts a linear variation of lift and pitching moment with incidence angle, and substantially under-predicts the induced drag. Results obtained from RANS and Euler agree well with experiment.

15 Aug 2016
TL;DR: In this paper, it is shown that when the maximum value of the span wise distribution of leading-edge suction on a finite wing reaches a critical value, LEV initiation takes place.
Abstract: : The aim of this research effort was to extend earlier work airfoil leading-edge vortex (LEV) shedding to finite-wing flows. The current research shows that leading-edge suction, which was shown in the earlier work to govern LEV formation in airfoils with rounded leading edges, also governs LEV formation on finite wings. It is shown that when the maximum value of the span wise distribution of leading-edge suction on a finite wing reaches a critical value, LEV initiation takes place. The critical value is the same as that for the corresponding airfoil section, allowing it to be determined from 2D experiments or computations. Further, the critical value is independent of motion kinematics so long as LEV formation is not preceded by significant trailing-edge flow reversal. This insight was used to augment an in viscid unsteady vortex lattice method (UVLM) to handle LEV shedding from finite wings by using a vortex sheet to model the LEV shedding along the span. By convecting the LEV sheet using local velocity, the UVLM was able to predict vortex-sheet roll up, which agreed well with high-order computations. The current research has brought to light important insights in the initiation of LEV shedding on finite wings, which can be used in low-order modeling and flow control.

Proceedings ArticleDOI
Anh Tuan Nguyen1, Jae-Hung Han1
TL;DR: In this paper, an insect wing structure is modeled based on data obtained from measurements on real hawkmoth (Manduca Sexta) wings using an extended unsteady vortex-lattice method.
Abstract: In this paper, an insect wing structure is modeled based on data obtained from measurements on real hawkmoth (Manduca Sexta) wings. The aerodynamics of insect wings is simulated by an extended unsteady vortex-lattice method. The finite-element model of a flexible hawkmoth wing is built and validated. A computer program, which couples the finite-element model with the aerodynamic model, is used to study the effects of fluid-structure interaction. Some important features due to the fluid-structure interaction in hovering and forward flight are observed in the present study.

Proceedings ArticleDOI
04 Jan 2016
TL;DR: In this paper, the design of a winglet for the Dassault Falcon 10 business jet is presented, where the configuration showing the best compromise between induced drag reduction, parasite drag and structural weight increase is selected.
Abstract: The design of a winglet for the Dassault Falcon 10 business jet is presented. The configuration showing the best compromise between induced drag reduction, parasite drag and structural weight increase was selected, where the design variables were winglet span and cant angle. For the determination of the best configuration, the change in drag was calculated using a vortex lattice method model of the aircraft, calibrated with respect to wind tunnel data and the weight penalty was estimated using empirical methods. For that winglet geometry, a RANS model was created and used to generate the aircraft drag polars. Also, a finite element model of the wing box, validated with respect to stress data, was used to estimate the structural reinforcement that the new winglet loads would require and, hence, their weight penalty. Using the new drag polars and structural weights, the aircraft range and fuel burn were calculated and compared to the baseline aircraft. At typical cruise lift coefficients, the net drag reduction was 4.8% at Mach 0.7 and 2.5% at Mach 0.8. For typical operation conditions, the range was increased by 66 NM (4.3%) and for a 1,200 NM mission, fuel burn is reduced by 3.9%. The maximum range increase and fuel savings were 3.3% and 3.8%, respectively.


Journal ArticleDOI
01 Jun 2016
TL;DR: In this paper, 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.
Abstract: 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.

Proceedings ArticleDOI
04 Jan 2016
TL;DR: In this article, a numerical iterative vortex lattice method is developed for post-stall flow past wing(s) where the separated flow is modeled using NY nascent vortex filaments.
Abstract: A numerical iterative vortex lattice method is developed for post-stall flow past wing(s) where the separated flow is modeled using NY nascent vortex filaments. The wing itself is modeled using NX×NY bound vortex rings, where NX and NY are the number of sections along the chord and span of the wing respectively. The strength and position of the nascent vortex along the chord corresponding to the local effective angle of attack are evaluated from the residuals in viscous and potential flow, i.e. (Cl)visc − (Cl)pot and (Cm)visc − (Cm)pot. Hence, the 2D airfoil viscous Cl − α and Cm − α is required as input (from experiment, numerical analysis or CFD). Aerodynamic characteristics and section distribution along span are predicted for 3D wings at post-stall angles of attack. Effect of initial conditions and existence of multiple solutions in the post-stall region is studied. Results are validated with experiment.

Proceedings ArticleDOI
15 Jun 2016
TL;DR: A modified and enlarged version of the UVLM is presented, which admits local mesh refinement of the body bound-vortex lattice by the introduction of a set of new elements, called transition elements.
Abstract: It is very well known that the non-lineal and unsteady vortex-lattice method (UVLM) produces better results when the vortex sheets, that simulate the boundary layer on the body and the free wakes, are discretized using uniform rectangular vortex-rings elements, producing structured lattices (or meshes). Moreover, the density of elements on these grids strongly affect the accuracy of the numerical simulations. So far, global mesh refinement is the only mechanism known to improve the precision of such results. In this article, a modified and enlarged version of the UVLM is presented, which admits local mesh refinement of the body bound-vortex lattice by the introduction of a set of new elements, called transition elements. Using these elements, it is possible to reduce the size of the vortex lines on specific areas of the vortex lattice in order to improve the accuracy of the results, while keeping larger vortex lines in the rest of the discretized bound-vortex sheet. The lattice, refined in this way, allows a significant reduction of the computational costs. The method developed was successfully validated by contrasting against previously published test cases.