Aerodynamics for Engineers

Bertin, John J.; Cummings, Russell M.

doi:10.1017/9781009105842

Cited by 36 publications

(37 citation statements)

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“…At the first time step, only the bound vortex rings are present on the wing surface. Each segment of the bound vortex rings will induce a velocity on each of the collocation points according to the Biot-Savart law [29]. At the end of the first time step, the bound vortex rings at the trailing edge of the wing are shed and moved at the local velocity to create the first row of the wake.…”

Section: The Unsteady Vortex Lattice Methodsmentioning

confidence: 99%

Role of Active Morphing in the Aerodynamic Performance of Flapping Wings in Formation Flight

Billingsley

Ghommem

Vasconcellos

et al. 2021

Drones

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Migratory birds have the ability to save energy during flight by arranging themselves in a V-formation. This arrangement enables an increase in the overall efficiency of the group because the wake vortices shed by each of the birds provide additional lift and thrust to every member. Therefore, the aerodynamic advantages of such a flight arrangement can be exploited in the design process of micro air vehicles. One significant difference when comparing the anatomy of birds to the design of most micro air vehicles is that bird wings are not completely rigid. Birds have the ability to actively morph their wings during the flapping cycle. Given these aspects of avian flight, the objective of this work is to incorporate active bending and torsion into multiple pairs of flapping wings arranged in a V-formation and to investigate their aerodynamic behavior using the unsteady vortex lattice method. To do so, the first two bending and torsional mode shapes of a cantilever beam are considered and the aerodynamic characteristics of morphed wings for a range of V-formation angles, while changing the group size in order to determine the optimal configuration that results in maximum propulsive efficiency, are examined. The aerodynamic simulator incorporating the prescribed morphing is qualitatively verified using experimental data taken from trained kestrel flights. The simulation results demonstrate that coupled bending and twisting of the first mode shape yields the highest propulsive efficiency over a range of formation angles. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a five-body V-formation incorporating coupled bending and twisting of the first mode at a formation angle of 140 degrees. These results indicate the potential improvement in the aerodynamic performance of the formation flight when introducing active morphing and bioinspiration.

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Section: The Unsteady Vortex Lattice Methodsmentioning

confidence: 99%

Role of Active Morphing in the Aerodynamic Performance of Flapping Wings in Formation Flight

Billingsley

Ghommem

Vasconcellos

et al. 2021

Drones

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“…The optimization problem selected to analyze the performance of the strategy presented in this work considers the NACA-0012 airfoil with sharp trailing edge at an AoA of = 0 • as the baseline geometry. The objective is to minimize the drag coefficient C D at flight conditions under uncertainty in a low-Mach-number turbulent flow regime, while providing a lift coefficient C L above a specified target (i) C ⋆ L = 0.375 , close to the typical values found for commercial transport airliners (Bertin 2002), or (ii) C ⋆ L = 0.75 for comparison.…”

Section: Problem Descriptionmentioning

confidence: 99%

Rapid aerodynamic shape optimization under uncertainty using a stochastic gradient approach

Jofre

Doostan

2022

Struct Multidisc Optim

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A common approach in aerodynamic design is to optimize a performance function—provided some constraints—defined by a choice of an aerodynamic model at nominal operating conditions. Practical experience indicates that such a deterministic approach may result in considerably sub-optimal designs when the adopted aerodynamic model does not lead to accurate predictions, or when the actual operating conditions differ from those considered in the design. One approach to address this shortcoming is to consider an average or robust design, wherein the statistical moments of the performance function, given the uncertainty in the operating conditions and the aerodynamic model, is optimized. However, when the number of uncertain inputs is large or the performance function exhibits significant variability, an accurate evaluation of these moments may require a large number of function evaluations at each optimization iteration, rendering the problem significantly expensive. To tackle this difficulty, we consider a variant of the stochastic gradient descent method where in each iteration, a stochastic approximation of the objective, constraints, and their gradients is generated. This is done via a small number of forward/adjoint solutions corresponding to random selections of the uncertainties. The methodology is applied to the robust optimization of the NACA-0012 airfoil subject to operating condition and turbulence model uncertainty. With a cost that is only a small factor larger than that of the deterministic methodology, the stochastic gradient approach significantly improves the performance of the aerodynamic design for a wide range of operating conditions and turbulence models.

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“…A prerequisite for the flight of a windscreen aircraft is the continuous blowing of an airstream onto the lifting rotor [4]. Although the wind-glider looks like a helicopter, it is closer to an aircraft.…”

Section: Introductionmentioning

confidence: 99%