Modeling of Wake Vortex Effects for Unmanned Air Vehicle Simulations

Saban, Deborah; Whidborne, James F.

doi:10.2514/6.2009-5686

Cited by 3 publications

(3 citation statements)

References 27 publications

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“…The circulation strength of the wake rings remains constant as they move away from the lifting surface, but they are allowed to roll up and stretch. Albeit dissipation could also be accounted for by implementing any of various models for wake decay 45,49,50 , this was not regarded necessary for the applications under study. …”

Section: Aerodynamic Modeling: Unsteady Vortex Lattice Methodsmentioning

confidence: 99%

“…However, the simplest remedy is to introduce a vortex-core to model the inner viscous part of the vortex filament. Several models have been proposed 35,39,45 , but in all of them the choice of core size lacks theoretical or physical justification. As a consequence, it has to be defined cautiously, since it can have a significant influence on the solution.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of Nonlinear Flexible Aircraft Dynamics Including Free-Wake Effects

Murua

Palacios

Graham

2010

AIAA Atmospheric Flight Mechanics Conference

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This paper addresses the unified aeroelastic and flight dynamics characterization of lowspeed slender-wing aircraft, including free-wake effects and aerodynamic interference. An analysis framework is presented that targets the prediction of stability and handling qualities of high-altitude long-endurance vehicles, which are prone to experience large wing excursions, leading to an inherently nonlinear and coupled problem between aerodynamics, elasticity and flight dynamics. In this work, the structural dynamics are based on a geometrically-exact composite beam model, discretized using displacement-based finite elements, and cast into an extended flexible-body dynamics model. The aerodynamic model is defined by a general unsteady vortex lattice method. The governing equations of motion of the integrated system are formulated in a tightly-coupled state-space form, which allows for the equations to be solved simultaneously. Verification of the model has been carried out for static and dynamic problems, including both rigid and flexible wings. Numerical studies are presented for the particular case of prescribed rigid-body motions, paying special attention to the likely interference between wake and tail. Results show that the current approach represents a suitable alternative for configuration analysis of flexible atmospheric vehicles, offering a good balance between degree of fidelity and computational cost. Nomenclature a = body-attached (global) reference frame p Δ = pressure jump across aerodynamic panel * , kl kl a a = aerodynamic influence coefficients R = beam local position vector B = deformed (local) reference frame s = arc length along reference line b = undeformed (local) reference frame t = physical time b Δ = spanwise dimension of aerodynamic panel V = beam local translational velocity Ba C = coordinate transformation matrix from a to B V ∞ = free-stream velocity c Δ = chordwise dimension of aerodynamic panel v = translational velocity of the a frame G = inertial (ground) frame of reference k v = downwash b w K ,K = number of bound and wake vortex-rings considered w = normal component of the non-vortical induced velocity K ,k = current and initial beam local curvatures X = coordinates on aerodynamic lattice p = position of the a frame with respect to G x = state vector Greek letters Γ = circulation strength Ω = beam local angular velocity γ = beam local force strain ω = angular velocity of the a frame ζ = quaternions Ψ = Cartesian Rotation Vector κ = beam local moment strain 2 Subscripts A = aerodynamic R = rigid-body b = bound, corresponding to lifting surface S = structural , , i j k = chordwise, spanwise and total panel counters w = wake Superscripts * • = corresponding to wake • = cross-product operator • = derivatives with time, t • = vector magnitude ′ • = derivatives with the curvilinear coordinate, s

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Section: Aerodynamic Modeling: Unsteady Vortex Lattice Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modeling of Nonlinear Flexible Aircraft Dynamics Including Free-Wake Effects

Murua

Palacios

Graham

2010

AIAA Atmospheric Flight Mechanics Conference

View full text Add to dashboard Cite

show abstract

“…The wake elements are then freely convected and rolled up according to the local flow velocity, and thus generate a vortex ring lattice representing the shed wake. The circulation strength of the wake rings remains constant as they are moved away from the lifting surface, and they are allowed to roll up and stretch; albeit dissipation could also be accounted for by implementing any of various models for wake decay [26,27], this was not regarded as necessary for the applications under study.…”

Section: B Vortex-lattice Modelingmentioning

confidence: 99%

Structural and Aerodynamic Models in Nonlinear Flight Dynamics of Very Flexible Aircraft

2010

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An evaluation of computational models is carried out for flight dynamics simulations on low-speed aircraft with very-flexible high-aspect ratio wings. Structural dynamic models include displacement-based, strain-based, and intrinsic (first-order) geometrically-nonlinear composite beams, while thin-strip and vortex lattice methods are considered for the unsteady aerodynamics. It is first shown that all different beam finite element models (previously derived in the literature from different assumptions) can be consistently obtained from a single set of equations. This approach has been used to expand existing strain-based models to include shear effects. Comparisons are made in terms of numerical efficiency and simplicity of integration in flexible aircraft flight dynamics studies. On the structural modeling, it was found that intrinsic solutions can be several times faster than conventional ones for aircraft-type geometries. For the aerodynamic modeling, thin-strip models based on indicial airfoil response are found to perform well in situations dominated by small amplitude dynamics around large quasi-static wing deflections, while large-amplitude wing dynamics require three-dimensional descriptions (e.g. vortex lattice)

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Assessment of Wake-Tail Interference Effects on the Dynamics of Flexible Aircraft

2012

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This work investigates the eect of aerodynamic interference in the coupled nonlinear aeroelasticity and ight mechanics of exible lightweight aircraft at low speeds.For that purpose, a geometrically-exact composite beam formulation is used to model the vehicle exible-body dynamics, by means of an intuitive and easily linearizable representation based on the displacement and Cartesian rotation vectors. The aerodynamics are modeled using the unsteady vortex-lattice method, which captures the instantaneous shape of the lifting surfaces and the free inviscid wake, including large deformations and interference eects. This results in a framework for Simulation of High Aspect Ratio Planes that provides a medium-delity representation of exibleaircraft dynamics with a modest computational cost. Previous independent studies on the structural-dynamics and aerodynamics modules are complemented here with the integrated simulation methodology, including vehicle trim, and linear and nonlinear time-domain solutions. A numerical investigation is next presented on a simple wingfuselage-tail conguration, assessing the interference eects between wing-wake and horizontal tail, and the downwash due to the proximity of the wake is shown to play a signicant role in the longitudinal dynamics of the vehicle. Finally, a brief discussion of direct wake-tail encounters is included to show the limitations of the approach.

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Modeling of Wake Vortex Effects for Unmanned Air Vehicle Simulations

Cited by 3 publications

References 27 publications

Modeling of Nonlinear Flexible Aircraft Dynamics Including Free-Wake Effects

Modeling of Nonlinear Flexible Aircraft Dynamics Including Free-Wake Effects

Structural and Aerodynamic Models in Nonlinear Flight Dynamics of Very Flexible Aircraft

Assessment of Wake-Tail Interference Effects on the Dynamics of Flexible Aircraft

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