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Luciano Demasi - One of the best experts on this subject based on the ideXlab platform.

  • Box Wing and Induced Drag: Compressibility Effects in Subsonic and Transonic Regimes
    AIAA Journal, 2020
    Co-Authors: Lorenzo Russo, Renato Tognaccini, Luciano Demasi
    Abstract:

    Prandtl introduced the best wing system or Box Wing a century ago and showed its exceptional lift-Induced Drag performance with respect to wing systems having the same wingspan and lift (Prandtl, L...

  • Minimum Induced Drag Theorems for Nonplanar Systems and Closed Wings
    Variational Analysis and Aerospace Engineering, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Rauno Cavallaro
    Abstract:

    An analytical formulation for the Induced Drag minimization of generic single-wing non-planar systems, biwings, and closed systems is presented. The method is based on a variational approach, which leads to the Euler–Lagrange integral equations in the unknown circulation distributions. The relationship between quasi-closed C-wings, biwings, and closed systems is discussed and several Induced Drag theorems/properties are introduced. It is shown that under optimal conditions these systems present the same minimum Induced Drag and the circulation can be obtained from a fundamental one by just adding a constant. The shape of the optimal aerodynamic load on the Box Wing is showed to change with the distance between the wings; differently that what assumed in previous works, it is not the superposition of a constant and an elliptical function.

  • minimum Induced Drag theorems for joined wings closed systems and generic biwings applications
    Journal of Optimization Theory and Applications, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Emanuele Rizzo, Rauno Cavallaro, Antonio Dipace
    Abstract:

    An invariant procedure for the minimization of Induced Drag of generic biwings and closed systems (Joined Wings) was presented in the companion paper (minimum Induced Drag theorems for Joined Wings, closed systems, and generic biwings: theory) and is now adopted to study several theoretical open questions regarding these configurations. It is numerically verified that a quasi-closed C-wing presents the same optimal Induced Drag and circulation of the corresponding closed system. It is also verified that when the two wings of a biwing are brought close to each other so that the lifting lines identify a closed path, the minimum Induced Drag of the biwing is identical to the optimal Induced Drag of the corresponding closed system. The optimal circulation of this case differs from the quasi-closed C-wing one by an additive constant. The non-uniqueness of the optimal circulation for a closed wing system is also addressed, and it is shown that there are an infinite number of equivalent solutions obtained by adding an arbitrary constant to a reference optimal circulation. This property has direct positive impact in the design of Joined Wings as far as the wing load repartition is concerned: The percentage of aerodynamic lift supported by each wing can be modified to satisfy other design constraints, and without Induced Drag penalty. Finally, the theoretical open question regarding the asymptotic Induced Drag behavior of Joined Wings, when the vertical aspect ratio approaches infinity, has been resolved. It has been shown that for equally loaded wings indefinitely distant from each other, the boxwing minimum Induced Drag tends to zero. In that condition, the upper and lower wings present a constant aerodynamic load. Prandtl's approximated formula for the minimum Induced Drag of a boxwing (Best Wing System) cannot be used to describe the asymptotic behavior. This work also shows that the optimal distribution over the equally loaded horizontal wings of a boxwing is not the superposition of a constant and an elliptical functions. This is an acceptable approximation only for small vertical aspect ratios (of aeronautical interest).

  • minimum Induced Drag theorems for joined wings closed systems and generic biwings theory
    Journal of Optimization Theory and Applications, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Antonio Dipace, Rauno Cavallaro
    Abstract:

    An analytical formulation for the Induced Drag minimization of closed wing systems is presented. The method is based on a variational approach, which leads to the Euler---Lagrange integral equation in the unknown circulation distribution. It is shown for the first time that the augmented Munk's minimum Induced Drag theorem, formulated in the past for open single-wing systems, is also applicable to closed systems, joined wings and generic biwings. The quasi-closed C-wing minimum Induced Drag conjecture discussed in the literature is addressed. Using the variational procedure presented in this work, it is also shown that in a general biwing, under optimal conditions, the aerodynamic efficiency of each wing is equal to the aerodynamic efficiency of the entire wing system (biwing's minimum Induced Drag theorem). This theorem holds even if the two wings are not identical and present different shapes and wingspans; an interesting direct consequence of the theorem is discussed. It is then verified (but yet not demonstrated) that in a closed path, the minimum Induced Drag of the biwing is identical to the optimal Induced Drag of the corresponding closed system (closed system's biwing limit theorem). Finally, the nonuniqueness of the optimal circulation for a closed wing system is rigorously addressed, and direct implications in the design of joined wings are discussed.

  • minimum Induced Drag theorems for multi wing systems
    AIAA Journal, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Rauno Cavallaro
    Abstract:

    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 mul...

J. Schirra - One of the best experts on this subject based on the ideXlab platform.

  • Accurate Induced Drag prediction for highly non-planar lifting systems
    2020
    Co-Authors: J. Schirra
    Abstract:

    For highly non-planar lifting systems like the box wing, Induced Drag predictions based on common potential-flow methods can have limited accuracy. This is primarily related to the linear, fixed-wake surrogate models, which neglect the correlation of the

  • Wake-Model Effects on Induced Drag Prediction of Staggered Boxwings
    Aerospace, 2018
    Co-Authors: J. Schirra, William Bissonnette, Götz Bramesfeld
    Abstract:

    For staggered boxwings the predictions of Induced Drag that rely on common potential-flow methods can be of limited accuracy. For example, linear, freestream-fixed wake models cannot resolve effects related to wake deflection and roll-up, which can have significant affects on the Induced Drag projection of these systems. The present work investigates the principle impact of wake modelling on the accuracy of Induced Drag prediction of boxwings with stagger. The study compares Induced Drag predictions of a higher-order potential-flow method that uses fixed and relaxed-wake models, and of an Euler-flow method. Positive-staggered systems at positive angles of attack are found to be particularly prone to higher-order wake effects due to vertical contraction of wakes trajectories, which results in smaller effective height-to-span ratios than compared with negative stagger and thus closer interactions between trailing wakes and lifting surfaces. Therefore, when trying to predict Induced Drag of positive staggered boxwings, only a potential-flow method with a fully relaxed-wake model will provide the high-degree of accuracy that rivals that of an Euler method while being computationally significantly more efficient.

  • highly non planar lifting systems a relative assessment of existing potential methodologies to accurately estimate the Induced Drag
    32nd AIAA Applied Aerodynamics Conference, 2014
    Co-Authors: J. Schirra, J. Watmuff, Michael Bauschat
    Abstract:

    The present work assesses the ability of existing potential-methodologies to accurately estimate the Induced Drag of highly non-planar lifting systems. Based on a phenomenological study, the impact of wake modeling on the Induced Drag characteristics is exemplarily evaluated for a rectangular-shaped biplane and a box wing configuration. This includes the influence on associated key design parameters like the height-to-span ratio and the longitudinal staggering. Representing the classical analysis case, the effect of variation of the freestream projected height-to-span ratio with the angle of attack is investigated for fixed geometric properties. For any non-zero staggering, non-linear wing-wake interactions, introduced by the rolled-up and force-free wake shape, are revealed to have noticeable influence on the estimation for the box wing configuration. In contrast to the biplane, the entire substitution of the force-free wake is not feasible. An accurate estimation involving higher angles of attack is found to be generally problematic.

  • Euler-based Induced Drag Estimation for Highly Non-planar Lifting Systems during Conceptual Design
    2013
    Co-Authors: J. Schirra, J. Watmuff
    Abstract:

    Implementation of Euler-based Induced Drag estimation is considered exemplary for two planar and two highly non-planar lifting systems employing farfield analysis technique. Basic Induced Drag characteristics are provided by means of established farfield analysis as well as on linear potential methodology employing a vortex-lattice approach. Euler-based span efficiencies are found to agree reasonably with those predicted by potential theory, although individual spanloads and downwash distribution differ considerably. Particularly for the crescent biplane, reduced downwash compensates performance penalties introduced by uneven distribution of lift. Supposed impact of non-linear flow filed properties like wake roll-up on Induced Drag characteristics of highly non-planar lifting systems could not be verified for configurations under consideration.

  • Induced Drag Computation with Wake Model Schemes for Highly Non-Planar Wing Systems
    2013
    Co-Authors: J. Hoefling, J. Schirra, A. Spohr, D. Schaefer
    Abstract:

    The capabilities of Induced Drag prediction for highly non-planar wing configurations are analyzed using a vortex-lattice, a relaxed-wake vortex-lattice and a higher order panel method. Therefore Surface Pressure, Trefftz-Plane and Trailing Edge analysis are studied using planar crescent and elliptical shaped lifting surfaces, concluding that the two latter methods achieve the desired accuracy. In order to study the influences of Drag-free and force-free wake model schemes on highly non-planar configurations, two biplane configurations are analyzed. Each method were found to have span efficiencies that agree well with lifting line theory, yet the relaxed-wake vortex-lattice and the higher order panel methods achieved more accurate results regarding Induced Drag prediction. For the same biplane configuration different downwash distributions and spanlaodings are found, depending on the utilized force-free or Drag-free wake model scheme. These differences are associated with the wake sheet and rollup behavior inherited by the force-free wake model scheme and verified by comparison to higher order methods.

Rauno Cavallaro - One of the best experts on this subject based on the ideXlab platform.

  • Minimum Induced Drag Theorems for Nonplanar Systems and Closed Wings
    Variational Analysis and Aerospace Engineering, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Rauno Cavallaro
    Abstract:

    An analytical formulation for the Induced Drag minimization of generic single-wing non-planar systems, biwings, and closed systems is presented. The method is based on a variational approach, which leads to the Euler–Lagrange integral equations in the unknown circulation distributions. The relationship between quasi-closed C-wings, biwings, and closed systems is discussed and several Induced Drag theorems/properties are introduced. It is shown that under optimal conditions these systems present the same minimum Induced Drag and the circulation can be obtained from a fundamental one by just adding a constant. The shape of the optimal aerodynamic load on the Box Wing is showed to change with the distance between the wings; differently that what assumed in previous works, it is not the superposition of a constant and an elliptical function.

  • minimum Induced Drag theorems for joined wings closed systems and generic biwings applications
    Journal of Optimization Theory and Applications, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Emanuele Rizzo, Rauno Cavallaro, Antonio Dipace
    Abstract:

    An invariant procedure for the minimization of Induced Drag of generic biwings and closed systems (Joined Wings) was presented in the companion paper (minimum Induced Drag theorems for Joined Wings, closed systems, and generic biwings: theory) and is now adopted to study several theoretical open questions regarding these configurations. It is numerically verified that a quasi-closed C-wing presents the same optimal Induced Drag and circulation of the corresponding closed system. It is also verified that when the two wings of a biwing are brought close to each other so that the lifting lines identify a closed path, the minimum Induced Drag of the biwing is identical to the optimal Induced Drag of the corresponding closed system. The optimal circulation of this case differs from the quasi-closed C-wing one by an additive constant. The non-uniqueness of the optimal circulation for a closed wing system is also addressed, and it is shown that there are an infinite number of equivalent solutions obtained by adding an arbitrary constant to a reference optimal circulation. This property has direct positive impact in the design of Joined Wings as far as the wing load repartition is concerned: The percentage of aerodynamic lift supported by each wing can be modified to satisfy other design constraints, and without Induced Drag penalty. Finally, the theoretical open question regarding the asymptotic Induced Drag behavior of Joined Wings, when the vertical aspect ratio approaches infinity, has been resolved. It has been shown that for equally loaded wings indefinitely distant from each other, the boxwing minimum Induced Drag tends to zero. In that condition, the upper and lower wings present a constant aerodynamic load. Prandtl's approximated formula for the minimum Induced Drag of a boxwing (Best Wing System) cannot be used to describe the asymptotic behavior. This work also shows that the optimal distribution over the equally loaded horizontal wings of a boxwing is not the superposition of a constant and an elliptical functions. This is an acceptable approximation only for small vertical aspect ratios (of aeronautical interest).

  • minimum Induced Drag theorems for joined wings closed systems and generic biwings theory
    Journal of Optimization Theory and Applications, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Antonio Dipace, Rauno Cavallaro
    Abstract:

    An analytical formulation for the Induced Drag minimization of closed wing systems is presented. The method is based on a variational approach, which leads to the Euler---Lagrange integral equation in the unknown circulation distribution. It is shown for the first time that the augmented Munk's minimum Induced Drag theorem, formulated in the past for open single-wing systems, is also applicable to closed systems, joined wings and generic biwings. The quasi-closed C-wing minimum Induced Drag conjecture discussed in the literature is addressed. Using the variational procedure presented in this work, it is also shown that in a general biwing, under optimal conditions, the aerodynamic efficiency of each wing is equal to the aerodynamic efficiency of the entire wing system (biwing's minimum Induced Drag theorem). This theorem holds even if the two wings are not identical and present different shapes and wingspans; an interesting direct consequence of the theorem is discussed. It is then verified (but yet not demonstrated) that in a closed path, the minimum Induced Drag of the biwing is identical to the optimal Induced Drag of the corresponding closed system (closed system's biwing limit theorem). Finally, the nonuniqueness of the optimal circulation for a closed wing system is rigorously addressed, and direct implications in the design of joined wings are discussed.

  • minimum Induced Drag theorems for multi wing systems
    AIAA Journal, 2016
    Co-Authors: Luciano Demasi, Giovanni Monegato, Rauno Cavallaro
    Abstract:

    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 mul...

  • invariant formulation for the minimum Induced Drag conditions of nonplanar wing systems
    AIAA Journal, 2014
    Co-Authors: Luciano Demasi, Giovanni Monegato, Antonio Dipace, Rauno Cavallaro
    Abstract:

    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 proced...

Kenneth D. Visser - One of the best experts on this subject based on the ideXlab platform.

  • Minimal Induced Drag for Non-planar Lifting Surfaces with Moderate and Small Aspect Ratio
    Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2020
    Co-Authors: Thomas Streit, Kenneth D. Visser, Carsten M. Liersch
    Abstract:

    The Induced Drag of non-planar wings is compared to that of planar wings which result from unfolding the non-planar ones. It is shown that due to the Induced lift, there exist non-planar configurations with positive span camber that have an overall aerodynamic performance increase in comparison to the planar ones. The Induced lift and increment of aerodynamic performance increases with decreasing aspect ratio. The effect is opposite for configurations with negative camber. Without the Induced lift, the positive non-planar configuration would have more Induced Drag. Analysis is performed using a lifting line method, which takes into account the Induced lift, and using Euler solutions. For the inviscid solutions, the Induced Drag is obtained with a far-field Drag analysis method.

  • A Computational Study of Induced Drag Behavior for Spanwise Cambered Wings
    28th AIAA Applied Aerodynamics Conference, 2010
    Co-Authors: Brent W. Pomeroy, Kenneth D. Visser
    Abstract:

    Results from lifting line theory, vortex lattice methods, and Euler techniques suggest that simple spanwise cambering of a planar wing, resulting in a reduced projected span but equivalent arc length and area, reduces the Induced Drag. Lifting line theory suggested a reduction of Induced Drag in positive cambered wings by almost 1% for certain configurations. Three-dimensional Euler flow solutions were obtained using the TetrUSS package from NASA Langley and suggested a Drag reduction of as much as 1.6%, or 4.3 Drag counts for the current configuration, with upward cambered wings. Viscous solutions were also run on the optimum Euler geometry and indicated reduced improvements of less than 1 count or 0.30%. Initial optimization with twist improved the Euler results to 2%.

  • Numerical Implications of Spanwise Camber on Minimum Induced Drag Configurations
    47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
    Co-Authors: Carsten M. Liersch, Thomas Streit, Kenneth D. Visser
    Abstract:

    Lifting line and Euler techniques have indicated that an elliptical planform cambered in the spanwise direction appears to have a lower Induced Drag than the uncambered, planar configuration, when both of then have identical arc lengths and the same wetted areas. In other words, a wing geometry with a lower projected span than the planar wing, only because of spanwise cambering, has been found to have a lower Induced Drag than the corresponding planar case. It was also noted that in the Euler solutions the theoretical minimum Induced Drag was not achieved on a planar configuration without applying a twist distribution. The increased efficiency of the non-planar configuration is due to Induced lift and without accounting for this Induced lift, the Induced Drag is larger then that of the corresponding unfolded planar wing. Induced lift and aerodynamic efficiency of the spanwise cambered configuration was observed to increase with reduced aspect ratio.

Mark I. Stockman - One of the best experts on this subject based on the ideXlab platform.

  • Giant Surface-Plasmon-Induced Drag Effect
    Imaging and Applied Optics Congress, 2010
    Co-Authors: Maxim Durach, Anastasia Rusina, Mark I. Stockman
    Abstract:

    We predict a giant surface-plasmon-Induced Drag-effect rectification (SPIDER). In nanowires, this giant SPIDER generates rectified THz potential up to 10V and electric fields up to 105-106V/cm. The giant SPIDER is an ultrafast effect.

  • giant surface plasmon Induced Drag effect in metal nanowires
    Physical Review Letters, 2009
    Co-Authors: Maxim Durach, Anastasia Rusina, Mark I. Stockman
    Abstract:

    : Here, for the first time we predict a giant surface-plasmon-Induced Drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. In nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to approximately 10(5)-10(6) V/cm. The giant SPIDER is an ultrafast effect whose bandwidth for nanometric wires is approximately 20 THz. It opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.

  • Giant surface-plasmon-Induced Drag effect in metal nanowires.
    Physical Review Letters, 2009
    Co-Authors: Maxim Durach, Anastasia Rusina, Mark I. Stockman
    Abstract:

    Here, for the first time we predict a giant surface-plasmon-Induced Drag-effect rectification (SPIDER), which exists under conditions of the extreme nanoplasmonic confinement. In nanowires, this giant SPIDER generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ∼10 5 ―10 6 V/cm. The giant SPIDER is an ultrafast effect whose bandwidth for nanometric wires is ∼20 THz. It opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.

  • giant surface plasmon Induced Drag effect spider in metal nanowires
    Proceedings of SPIE, 2009
    Co-Authors: Maxim Durach, Anastasia Rusina, Mark I. Stockman
    Abstract:

    Here, for the first time we predict a giant surface plasmon-Induced Drag effect (SPIDEr), which exists under conditions of the extreme nanoplasmonic confinement. Under realistic conditions, in nanowires, this giant SPIDEr generates rectified THz potential differences up to 10 V and extremely strong electric fields up to ~ 105 ~ 106 V/cm. The SPIDEr is an ultrafast effect whose bandwidth for nanometric wires is ~ 20 THz. The giant SPIDEr opens up a new field of ultraintense THz nanooptics with wide potential applications in nanotechnology and nanoscience, including microelectronics, nanoplasmonics, and biomedicine.