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Showing papers on "Lift-induced drag published in 2007"


Journal ArticleDOI
TL;DR: In this paper, a NavierStokes solver, the e N method transition model, and a Reynolds-averaged two-equation closure were coupled to study the low Reynolds number flow characterized with laminar separation and transition.
Abstract: 4-10 5 . In order to gain better understanding of the fluid physics and associated aerodynamics characteristics, we have coupled (i) a NavierStokes solver, (ii) the e N method transition model, and (iii) a Reynolds-averaged two-equation closure to study the low Reynolds number flow characterized with laminar separation and transition. A new intermittency distribution function suitable for low Reynolds number transitional flow is proposed and tested. To support the MAV applications, we investigate both rigid and flexible airfoils, which has a portion of the upper surface mounted with a flexible membrane, using SD7003 as the configuration. Good agreement is obtained between the prediction and experimental measurements regarding the transition location as well as overall flow structures. In the current transitional flow regime, though the Reynolds number affects the size of the laminar separation bubble, it does not place consistent impact on lift or drag. The gust exerts a major influence on the transition position, resulting in the lift and drag coefficients hysterisis. It is also observed that thrust instead of drag can be generated under certain gust condition. At α=4 o , for a flexible wing, self-excited vibration affects the separation and transition positions; however, the time-averaged lift and drag coefficients are close to those of the rigid airfoil.

236 citations


Journal ArticleDOI
TL;DR: In this paper, the flow characteristics over a NACA4412 airfoil were studied in a low turbulence wind tunnel with moving ground simulation at a Reynolds number of 3.0 x 105 by varying the angle of attack from 0 to 10 deg and ground clearance of the trailing edge from 5% of chord to 100%.
Abstract: The flow characteristics over a NACA4412 airfoil are studied in a low turbulence wind tunnel with moving ground simulation at a Reynolds number of 3.0 x 105 by varying the angle of attack from 0 to 10 deg and ground clearance of the trailing edge from 5% of chord to 100%. The pressure distribution on the airfoil surface was obtained, velocity survey over the surface was performed, wake region was explored, and lift and drag forces were measured. To ensure that the flow is 2-D, particle image velocimetry measurements were performed. A strong suction effect on the lower surface at an angle of attack of 0 deg at the smallest ground clearance caused laminar separation well ahead of the trailing edge. Interestingly, for this airfoil, a loss of upper surface suction was recorded as the airfoil approached the ground for all angles of attack. For angles up to 4 deg, the lift decreased with reducing ground clearance, whereas for higher angles, it increased due to a higher pressure on the lower surface. The drag was higher close to the ground for all angles investigated mainly due to the modification of the lower surface pressure distribution.

137 citations


Journal ArticleDOI
TL;DR: In this paper, a control volume analysis is presented to analyze the jet effect on the co-flow jet airfoil with injection and suction and on the airfoils with injection only.
Abstract: A control volume analysis is presented in this paper to analyze the jet effect on the coflow jet airfoil with injection and suction and on the airfoil with injection only. The formulations to calculate the duct's reactionary forces that must be included for the lift and drag calculation are given. The computational fluid dynamics solutions based on the Reynolds-averaged Navier-Stokes model are used to provide the breakdowns of lift and drag contributions from the airfoil surface force integral and jet duct's reactionary forces. The results are compared with experiment for validation. The duct reactionary forces are also validated with the result of a 3-D computational fluid dynamics calculation of the complete airfoil with jet ducts and wind tunnel walls. The study indicates that the suction occurring on the airfoil suction surface of the coflow jet airfoil is more beneficial than the suction occurring through the engine inlet such as the airfoil with injection only. For the airfoil with injection only, the drag actually acted on the aircraft, or the equivalent drag, is significantly larger than the drag measured by the wind tunnel balance due to the ram drag and captured area drag when the jet is drawn from the freestream. For a coflow jet airfoil, the drag measured by the wind tunnel balance is the actual 2-D drag that the aircraft will experience. A coflow jet airfoil does not have the ram drag and captured area drag. For a coflow jet airfoil, the suction penalty is offset by the significant circulation enhancement The coflow jet airfoil with both injection and suction yields stronger mixing, larger circulation, more filled wake, higher stall angle of attack, less drag, and lower energy expenditure.

116 citations


Proceedings ArticleDOI
08 Jan 2007
TL;DR: In this paper, the roles of the plunging and pitching amplitude and frequency, and Strouhal number were studied for a symmetric plunging airfoil NACA0012 at zero geometric angle of attack and chord Reynolds number of 2×10 4, at the same plunging frequency.
Abstract: It is known that plunging airfoil can produce both lift and thrust with certain combination of plunging amplitude and frequency. Motivated by our interest in micro air vehicles (MAVs), we utilize a NavierStokes equation solver to investigate the aerodynamics of a flapping airfoil. The roles of the plunging and pitching amplitude and frequency, and Strouhal number are studied. For a symmetric plunging airfoil NACA0012 at zero geometric angle of attack and chord Reynolds number of 2×10 4 , at the same plunging frequency, it can produce either drag or thrust depending on the plunging amplitude. At the considered plunging amplitude (from 0.0125c to 0.075c), the flow history has more influence than the kinematic angle of attack to determine the lift. When drag is produced, the viscous force dominates the total drag with decreasing influence as the plunging amplitude increases. For an airfoil experiencing combined plunge and pitch motion, both thrust and input power increase with the Strouhal number (within the range of 0.03 to 0.5). For the case studied, the thrust is induced by the lift, which approximately follows the curve of the kinematic angle of attack. Leading edge vortex moves downstream and interacts with the trailing edge vortex. We also study the impact of gust on stationary airfoil and flapping airfoil. Within the range of the parameters tested, for stationary airfoil the lift is in phase with the velocity but the drag is slightly out of phase. For flapping airfoil, neither lift nor drag is in phase with the velocity. Nomenclature CD =Drag coefficient per unit span CL =Lift coefficient per unit span CP =input power coefficient CP,mean =time-averaged input power coefficient CT =thrust coefficient CT,mean =time-averaged thrust coefficient c =Chord length

76 citations


Book ChapterDOI
01 Jan 2007
TL;DR: In this paper, the authors summarize the empirical information for computation of the drag, lift and virtual mass forces in multiphase flow analysis, which can be used in the computational analysis based on coarse meshes in the space.
Abstract: The pressure distribution around a particle moving in a continuum is nonuniform. Integrating the pressure distribution over the surface one obtains a resulting force that is different from zero. As shown in Vol. I, Chapter 6.2, the different spatial components of the integral correspond to different forces: drag, lift and virtual mass forces. The averaging procedure over a family of particles gives some averaged forces which can be used in the computational analysis based on coarse meshes in the space. The purpose of this section is to summarize the empirical information for computation of the drag, lift and virtual mass forces in multiphase flow analysis.

57 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical method for predicting minimum induced-drag conditions in a nonplanar lifting system is presented based on lifting line theory and the small perturbation acceleration potential.
Abstract: A theoretical method for predicting minimum induced-drag conditions in a nonplanar lifting systems is presented in this paper. The procedure is based on lifting line theory and the small perturbation acceleration potential. Under the hypotheses of linearity and rigid wake aligned with the freestream, optimality conditions are formulated using the Euler-Lagrange integral equation with constraints on fixed total lifting force and wing span. Particular attention is paid to analysis and numerical treatment of the Hadamard finite-part integrals involved in the solution process. The minimum induced-drag problem is then formulated and solved numerically and analytically. In the case of annular wings, closed-form expressions for the optimal circulation distribution, the normalwash, the induced-drag coefficient, and the efficiency are presented. Optimal annular wings and C-wings are extensively analyzed

51 citations


Proceedings ArticleDOI
08 Jan 2007
TL;DR: The results from the third AIAA Drag Prediction Workshop using the unstructured mesh Reynolds averaged Navier-Stokes (RANS) solver NSU3D are presented in this article.
Abstract: Results from the third AIAA Drag Prediction Workshop using the unstructured mesh Reynolds averaged Navier-Stokes (RANS) solver NSU3D are presented. Computations include a grid convergence study on a transonic wing-body and wing-body-fairing configuration at a fixed CL condition using grids up to 41 million points, as well as an incidence sweep (drag polar) at fixed Mach and Reynolds number. A second set of results on a pair of closely related wing geometries is also described, including a grid convergence study at fixed incidence, and an incidence sweep (drag polar) for both wing geometries. For all cases, approximate second-order accurate grid convergence characteristics are demonstrated, with overall accuracy and eciency comparable to other structured, overset, and unstructured workshop calculations. However, it is found that diering grid converged results may be inferred based on dierent families of self-similar coarse and fine grid sequences, particularly for values such as absolute drag at fixed incidence. More consistent grid convergence for idealized drag values (omitting induced drag) is observed, thus validating the procedure of performing grid convergence studies at fixed CL. These grid convergence issues are attributed to the large range of disparate scales which must be resolved in aerodynamic flows, and point to the need for further advances in quantifying and resolving discretization errors for such problems. Over the last five years, the AIAA Applied Aerodynamics Committee has sponsored three Drag Prediction Workshops (DPW), with the aim of assessing the state-of-the-art of current Computational Fluid Dynamics (CFD) solvers at predicting absolute and incremental drag changes on generic transonic transport aircraft configurations.

44 citations


Journal ArticleDOI
TL;DR: In this article, the maximum lift coefficient for a wing was predicted from knowledge of wing geometry and maximum airfoil section lift coefficient, including the effects of twist and sweep, by using a method that allows one to predict the wing's maximum lift coefficients for a given planform with a known twist distribution, while keeping the total amount of required twist at a practical level.
Abstract: A method is presented that allows one to predict the maximum lift coefficient for a wing from knowledge of wing geometry and maximum airfoil section lift coefficient. The method applies to wings of arbitrary planform and includes the effects of twist and sweep. In addition to predicting the section lift distribution for a wing of known planform with a known twist distribution, the method can be used to predict the twist distribution, which will produce any desired section lift distribution along the span of an unswept wing of any given planform. The method is shown to predict the twist distribution required to minimize induced drag and is also used to predict the twist distribution that maximizes the wing lift coefficient, while keeping the total amount of required twist at a practical level.

41 citations


Journal ArticleDOI
TL;DR: In this article, a forward-facing supersonic air jet for a 60° apexangle blunt cone at a flow Mach number of 8 was used to reduce the aerodynamic drag.
Abstract: Substantial aerodynamic drag, while flying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone configuration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apexangle blunt cone at a flow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefficient has been observed with the injection of a supersonic gas jet.

24 citations


Proceedings ArticleDOI
25 Jun 2007
TL;DR: In this article, the aerodynamic properties of a single-winged aircraft in formation have been evaluated using a limited number of flight formation configurations comprising identical wings with and without winglets, and the results showed that up to 60% lift induced drag reduction can be achieved on a Trail aircraft following a larger Lead wing.
Abstract: The idea of flying commercial aircraft in formation to reduce fuel usage, has been around for some time. There are many results available using idealized approaches e.g. vortex lattice formulations. In view of the greater importance being attached to environmental aspects, the need has arisen to evaluate the possible advantages and disadvantages. A previous paper was concerned with a limited number of flight formation configurations comprising identical wings. Even then the predicted induced drag reductions of near 30%, affording overall drag reductions of the order of 15-20%. This paper steps up the analysis level exploiting a recently developed design method that allows span loading and camber control on wings without and with winglets. The method has been adapted to assess the aerodynamics of wings in formation and then to re-design them to eliminate induced roll effects. We have extended the analysis by enlarging the formation size, varying the spacing parameters (x, y and z) and varying the relative sizes of the aircraft within the formation The technique has proved to be easy and robust in use. It is enlightening as it gives, at every stage, a feel for what is happening in terms of camber development, pressure distributions and Centre of Pressure location. We have been able to define areas of specific interest that are worthy of further analysis in terms of formation geometry. Conversely, formation geometries that are not beneficial (drag penalties or the need for prohibitive control surface deflections) can be avoided. Lift induced drag reductions of up to 60% may be achieved on a Trail aircraft following a larger Lead wing. A limited number of results using an Euler solver reflect benefits of the same order for equiand varying sized aircraft in formation. Several avenues of further work and development have arisen.

22 citations


Patent
10 Sep 2007
TL;DR: In this article, a control signal indicating a left turn increases the incidence angle on the left wing and reduces it on the right wing is used to control the flight direction of an aircraft.
Abstract: An aircraft that is enabled to turn in a desired direction, and a method for controlling the flight direction of an aircraft, by employing differential drag on the respective wings. A control means that receives a control signal indicating a left turn increases the incidence angle on the left wing and reduces it on the right wing. For a right turn the opposite action is performed. The aircraft comprises airfoils that have increased drag as the incidence angle increases but have a generally constant lift.

Journal ArticleDOI
01 Jul 2007
TL;DR: In this article, a new CFD-based method aimed at predicting wind turbine aerodynamics, where velocity and pressure discontinuities are used to model the vortical system that creates lift on the turbine blades.
Abstract: This paper presents the recent developments of a new CFD-based method aimed at predicting wind turbine aerodynamics, where velocity and pressure discontinuities are used to model the vortical system that creates lift on the turbine blades. To illustrate the ability of the present model to predict induced wake effect, the case of the taper wing is thoroughly analyzed and effects of both domain discretization and convection scheme are presented. Results are mitigated regarding predicted performance of induced drag, but accurate induced and upstream flow angles values are obtained. The method is even shown to be a useful calculator for the relationship between inflow angle measured upstream and effective angle of attack of a wing section. Interesting results for the NREL phase VI rotor have been obtained showing improvement of the method upon actuator-disk approach in handling tip vortices effect on the blade aerodynamics.

Proceedings ArticleDOI
08 Jan 2007
TL;DR: This paper steps up the analysis level exploiting a recently developed design method that allows span loading and camber control on wings with without winglets, adapted to assess the aerodynamics of wings in formation and then to redesign them to eliminate induced roll effects.
Abstract: The idea of flying commercial aircraft in formation to reduce fuel usage, has been around for some time. There are many results available using idealized approaches e.g. vortex lattice formulations. In view of the greater importance being attached to environmental aspects, the need has arisen to evaluate the possible advantages and disadvantages. This paper steps up the analysis level exploiting a recently developed design method that allows span loading and camber control on wings with without winglets. The method has been adapted to assess the aerodynamics of wings in formation and then to redesign them to eliminate induced roll effects. From a limited number of flight formation configurations assessed so far, the method predicts induced drag reductions of near 30%, affording overall drag reductions of the order of 15%. The benefits may well be larger, using other formation spacing parameters. Limited results using an Euler solver reflect benefits of the same order. The technique has proved to be easy and robust in use. It is enlightening as it gives, at every stage, a feel for what is happening in terms of camber development, pressure distributions and Centre of Pressure location. Favourable characteristics of the configuration can be enhanced whereas those that are not beneficial can be minimised or avoided as the design progresses Several avenues of further work and development have arisen.

Journal ArticleDOI
TL;DR: In this article, a multi-row disk (MRD) was proposed, which has a cone and stabilizer disks being arranged in the axial direction, which can arbitrarily change its aerodynamic characteristics by translating stabilizer disk.

Patent
21 May 2007
TL;DR: In this paper, a method and apparatus for varying the twist of a wing such that induced drag is minimized or reduced during cruise and lift is maximized or increased at least during takeoff and landings is presented.
Abstract: A method and apparatus for varying the twist of a wing such that induced drag is minimized or reduced during cruise and lift is maximized or increased at least during takeoff and landings. In addition, variations in the twist may produce yawing and rolling moments. The twist amount is varied pursuant to the operating conditions, including those parameters used to determine the lift coefficient. The twist for reducing induced drag and/or improving lift may be employed by geometric or aerodynamic twist, including full span control surfaces used to provide roll control, high-lift and reduced induced drag. The twist may also be employed by twisting just a portion of the wing or the entire wing, either geometrically or aerodynamically.

Proceedings ArticleDOI
23 Apr 2007
TL;DR: In this article, an inverse optimization technique is used to manipulate the spanwise lift distribution resulting in the minimization of the induced drag on a high aspect ratio rectangular wing at subsonic and transonic flight conditions.
Abstract: The induced drag on wings is reduced at off-design cruise conditions with simulated active conformal control surface deflections modeled through transpiration boundary conditions with an Euler CFD program, the Air Vehicles Unstructured Solver (AVUS). An inverse optimization technique is used to manipulate the spanwise lift distribution resulting in the minimization of the induced drag. The method is demonstrated on a high aspect ratio rectangular wing at a subsonic and transonic flight conditions. The control surfaces deflections are calibrated to determine the extent to which their effect can be matched by a transpiration boundary condition. The CoNstrained MiNimization(CONMIN) program is used to minimize a squared error objective function. It is determined that the use of transpiration boundary conditions can drastically reduce the grid requirements and complexity associated with grid motion and deformation.

01 Jan 2007
TL;DR: In this paper, the aerodynamic properties of a single-winged aircraft in formation have been evaluated using a limited number of flight formation configurations comprising identical wings with and without winglets, and the results showed that up to 60% lift induced drag reduction can be achieved on a Trail aircraft following a larger Lead wing.
Abstract: The idea of flying commercial aircraft in formation to reduce fuel usage, has been around for some time. There are many results available using idealized approaches e.g. vortex lattice formulations. In view of the greater importance being attached to environmental aspects, the need has arisen to evaluate the possible advantages and disadvantages. A previous paper was concerned with a limited number of flight formation configurations comprising identical wings. Even then the predicted induced drag reductions of near 30%, affording overall drag reductions of the order of 15-20%. This paper steps up the analysis level exploiting a recently developed design method that allows span loading and camber control on wings without and with winglets. The method has been adapted to assess the aerodynamics of wings in formation and then to re-design them to eliminate induced roll effects. We have extended the analysis by enlarging the formation size, varying the spacing parameters (x, y and z) and varying the relative sizes of the aircraft within the formation The technique has proved to be easy and robust in use. It is enlightening as it gives, at every stage, a feel for what is happening in terms of camber development, pressure distributions and Centre of Pressure location. We have been able to define areas of specific interest that are worthy of further analysis in terms of formation geometry. Conversely, formation geometries that are not beneficial (drag penalties or the need for prohibitive control surface deflections) can be avoided. Lift induced drag reductions of up to 60% may be achieved on a Trail aircraft following a larger Lead wing. A limited number of results using an Euler solver reflect benefits of the same order for equi- and varying sized aircraft in formation. Several avenues of further work and development have arisen.

Journal ArticleDOI
TL;DR: In this article, a simple pendulum is designed and used in a wind tunnel to measure the drag force exerted by a moving stream of air on a spherical object, which is then used in experiments to measure drag forces exerted on smooth balls and on golf balls.
Abstract: While it is well known that the presence of dimples reduces the drag force exerted on a golf ball, demonstrations of this phenomenon are not common. A simple pendulum is designed and used in a wind tunnel to measure the drag force exerted by a moving stream of air on a spherical object. This pendulum is then used in experiments to measure drag forces exerted on smooth balls and on golf balls in order to compare the results. Data collected from 12 balls tested at speeds ranging from 54to180km∕h demonstrate that the presence of dimples on the surface of golf balls causes them to experience drag forces that are smaller than those on smooth balls of the same diameters and weights.

Journal ArticleDOI
TL;DR: In this article, a time-area-averaged momentum stream tube model is proposed to provide useful functional relations for the cruise velocity, power, and propulsive efficiency in forward flapping flight.
Abstract: This paper formulates a time-area-averaged momentum stream tube model to provide the useful functional relations for the cruise velocity, power, and propulsive efficiency in forward flapping flight. This model is a direct generalization of the classical actuator disk theory by taking into account the effects of the unsteadiness and spatial nonuniformity of velocity in a momentum stream tube. It is found that the functional relation for the time-areaaveraged power required in flapping flight is almost the same as that given by the classical lifting-line theory for a fixed wing. The flapping span efficiency is introduced, and its physical meaning and significant role in the power relationareinterpreted.The flappingpropulsiveefficiencyisrelatedtothe flappingspanefficiency,normalizedtotal fluctuating kinetic energy, and wing aspect ratio. The use of this model to fit the collected data for birds allows estimating the flapping span efficiency, parasite, and induced drag coefficients and propulsive efficiency. Nomenclature A = effective area of actuator disk or cross-section area of momentum stream tube Ab = circular area of a diameter of wingspan AR = wing aspect ratio b = wingspan CDPara = parasite drag coefficient

Journal ArticleDOI
TL;DR: In this paper, a piecewise linear model (PLM) is used to estimate the forcing frequency spectrum and interpolate or extrapolate the model to provide estimates of the spectrum at different points in the parameter space.
Abstract: A method is proposed to estimate the flow-induced drag on the actuator arm inside a hard disk drive. Typically, drag forces and moments on the actuator are computed as part of a computational fluid dynamics (CFD) solution of the flow field in the entire drive. Unidirectional coupling from the flow to the structure is then imposed to determine the structural response of the arm to the flow induced forcing. The methodology proposed here aims to reduce the simulation time associated with the flow calculations by directly estimating the forcing functions. The approach involves fitting a piecewise linear model (PLM) to the forcing frequency spectrum and interpolating or extrapolating the model to provide estimates of the spectrum at different points in the parameter space. A simple guideline for the formulation of such models is the conservation of energy between the CFD and PLM spectrum. Numerical experiments show that the linear models predict the behavior of arm to within 3% accuracy of the full CFD solution. The proposed technique is applied to two parameters: the disk RPM and the radial position of the arm. Clear trends are manifested for both parameters, making it possible to use this method to estimate forcing functions for a range of disk speeds and radial positions of the arm. This technique opens up the possibility of flow related design or optimization, which was previously thought to be prohibitively expensive.

Scott Monsch1
01 Jan 2007
TL;DR: In this article, the authors used a wake integral analysis to estimate the induced drag of an untwisted, finite rectangular wing (NACA 0012, AR = 6.7) using an Euler-based computational fluid dynamic solver.
Abstract: The purpose of this study was to validate an approach to estimating the induced drag on a finite wing by using a wake integral analysis. The long-term goal is related to developing an aerodynamic-structural systems integrated design methodology for wings through the use of a transpiration boundary condition to control the spanwise lift distribution throughout a typical aircraft mission so as to minimize lift–induced drag. The short term goal addressed by this study is to develop a methodology to extract accurate and robust calculations of the induced drag from second order numerical solutions. Numerical results for an untwisted, finite rectangular wing (NACA 0012, AR = 6.7) using no flap deflections are compared against theoretical lifting line predictions. The numerical approach used an Euler-based computational fluid dynamic (CFD) solver. An in-house lifting line code was used to predict the theoretical reference values. By dividing the wing into twenty span-wise sections and using a surface integral of pressure at each section, a span-wise lift distribution was extracted from the CFD solution. Under flow conditions representing subsonic and transonic flows (Mach 0.3 – 0.7) at small angles of attack, the comparison between the predicted numerical and lifting-line spanwise lift distributions show good agreement with a maximum deviation of only 2.4% over the wing span. The induced drag was extracted from the downstream wake using a wake integral technique referred to as Trefftz plane analysis. This approach was attempted because (1) there are known inherent inaccuracies associated with using the more common surface integral method for calculating the drag of a wing, and (2) the wake integral approach directly isolates the induced drag from other drag (viscous and wake) components. The predictions for induced drag based on surface integration, wake integration and lifting line methods are compared. The numerical induced drag results show a dependency on the downstream location of the Trefftz plane. Near wake and compressible flow corrections were applied to improve the induced drag predictions by wake integration. The wake integration approach is susceptible to artificial dissipation due to the numerical flow grid used, which provides an error that increases as the position of the Trefftz plane moves further downstream. Attempts to estimate the extent of this effect and to correct for it are discussed. The numerical solution of the Euler equations demonstrates successful implementation of the wake integral method via a Trefftz Plane analysis of the induced drag. The study details an initial effort to identify and to quantify the numerical uncertainties associated with the simulation and, specifically, the induced drag prediction.


Journal ArticleDOI
TL;DR: In this paper, an investigation of the dependence of the lift-induced drag coefficient of a square-tipped, cambered wing model on Reynolds number for Re ≥ 1/2πeAR was conducted, based on the vorticity distribution inferred from the near-field cross-flow velocity measurements of the tip vortex.
Abstract: An investigation of the dependence of the lift-induced drag coefficient C Di of a square-tipped, cambered wing model on Reynolds number for Re ≤ 1 × 106 was conducted. Computed based on the vorticity distribution inferred from the near-field cross-flow velocity measurements of the tip vortex, different C Di prediction schemes were used. The effect of measurement plane size and grid resolution on the C Di calculations was also identified. The C Di estimated by the integral method was found to increase with increasing Re and was below the C Di = C l 2 /πeAR prediction. Limits on the measurement plane size and grid resolution were determined to be at least 40% larger than the vortex outside diameter and no larger than 0.63% chord, respectively, in order to provide a good estimate of the induced drag.

01 Jan 2007
TL;DR: The Flexible Composite Surface Deturbulator (FCSDSD) as mentioned in this paper is a flexible composite surface deturbulator tape that is applied to the upper surface of the wing of a standard Cirrus sailplane to mitigate turbulence producing vortices.
Abstract: Multiple in flight sink-rate measurements of a Standard Cirrus sailplane verified 18% increase in average best glide ratio (L/D) by treating 8% of the mean aerodynamic chord of the wing upper surface with a passive Flexible Composite Surface Deturbulator tape. The periodic ridged substrate of an optimized Deturbulator mitigates turbulence producing vortices by breaking long wavelength flow induced oscillations of the flexible surface. Attenuating turbulence can be used to promote a thin nearly stagnant non-dissipative separated zone on top of the wing. When optimized this increases the effective airfoil camber while eliminating skin-friction and pressure drag. Closer examination of the sink-rate data alludes to the possibility of increasing L/D by 100% when such conditions are realized.

Proceedings ArticleDOI
08 Jan 2007
TL;DR: In this paper, the authors compared numerical and lifting-line lift distributi ons, under flow conditions representing Mach 0.3 − 0.7 subsonic and transonic flows at small angle s of attack, with a maximum deviation of only 2.4% over the wing span.
Abstract: distribution over a finite wing throughout a typical aircraft mission for minimizing lift – induced drag. Our ultimate goal requires extracting accurate and robust calculations of induced drag from the numerical solutio ns. We compare computational fluid dynamics numerical results for an untwisted, finite rectangular wing (NACA 00 12 , AR = 6.7 ) using no flap deflections against theoretical lifting line results. A comparison of the numerical and lifting -line lift distributi ons, under flow conditions representing Mach 0.3 – 0.7 subsonic and transonic flows at small angle s of attack, shows good agreement with a maximum deviation of only 2.4% over the wing span. The i naccuracies associated with the common surface integral meth od of calculating drag and the inability to isolate induced drag from other drag components prompted our approach of us ing a wake integral method. The numerical solution of the Euler equations demonstrate s successful implementation of the wake integral met hod via a Trefftz Plane analysis of the induced drag. We also present an initial effort to identify and to quantify the numerical uncertainties associated with the simulation .

Journal ArticleDOI
TL;DR: In this article, the minimum drag of the configuration (airfoil or wing) occurs at zero lift and the contribution of pressure drag (kpC 2 L for the airfoil) or pressure and induced (vortex) drag(kp iC l for the wing).
Abstract: where, by convention (excluding the k term), uppercase subscripts apply to wings and lowercase subscripts apply to airfoils. The first term on the right-hand side is the drag coefficient at zero lift and the second term represents the contribution of pressure drag (kpC 2 L for the airfoil) or pressure and induced (vortex) drag (kp iC l for the wing). For wings, both the pressure component of the profile drag coefficient kpC 2 L and the planform-dependent induced drag coefficient kiC 2 L vary with the square of the lift coefficient. This makes their separation difficult [thus the combination kp i parameter in Eq. (1b)]. Equations (1a) and (1b) are used as an approximation in performance estimates for preliminary design, as well as for interpretation and quantification of experimental and computational data. The form of Eq. (1) implies that the minimum drag of the configuration (airfoil or wing) occurs at zero lift. This is generally true for symmetrical airfoils or wings. For cambered airfoils or cambered section wings, a more representative approximation is of the form

Proceedings ArticleDOI
08 Jan 2007
TL;DR: In this paper, the maximum lift coefficient for a wing was predicted from knowledge of wing geometry and maximum airfoil section lift coefficient, including the effects of twist and sweep, by using a method that allows one to predict the wing's maximum lift coefficients for a given planform with a known twist distribution, while keeping the total amount of required twist at a practical level.
Abstract: A method is presented that allows one to predict the maximum lift coefficient for a wing from knowledge of wing geometry and maximum airfoil section lift coefficient. The method applies to wings of arbitrary planform and includes the effects of twist and sweep. In addition to predicting the section lift distribution for a wing of known planform with a known twist distribution, the method can be used to predict the twist distribution, which will produce any desired section lift distribution along the span of an unswept wing of any given planform. The method is shown to predict the twist distribution required to minimize induced drag and is also used to predict the twist distribution that maximizes the wing lift coefficient, while keeping the total amount of required twist at a practical level.


01 Mar 2007
TL;DR: In this paper, a Navier-Stokes equation solver is used to investigate the aerodynamics of a flapping airfoil and the roles of plunging and pitching amplitude and frequency, and Strouhal number are studied.
Abstract: : A Navier-Stokes equation solver is utilized to investigate the aerodynamics of a flapping airfoil. The roles of plunging and pitching amplitude and frequency, and Strouhal number are studied. For a NACA0012 airfoil at zero geometric angle of attack, chord Reynolds number of 20,000 and at a given plunging frequency, either drag or thrust is produced, depending on the plunging amplitude. When drag is produced, the viscous force dominates the total drag with decreasing influence as the plunging amplitude increases. At the considered plunging amplitude (from 0.0125c to 0.075c), flow history has more influence than the kinematic angle of attack in determining lift. For an airfoil experiencing combined plunge and pitch motion, both thrust and input power increase with the Strouhal number (within the range of 0.03 to 0.5). For the case studied, the thrust is induced by the lift, which follows approximately the curve of kinematic angle of attack. Leading edge vortex moves downstream and interacts with the trailing edge vortex. The impact of a gust on a stationary and flapping airfoil is also studied.