Vortex lattice method

About: Vortex lattice method is a research topic. Over the lifetime, 779 publications have been published within this topic receiving 9242 citations.

Errata and Addenda to "Application of Oscillatory Aerodynamic Theory to Estimation of Dynamic Stability Derivatives"

Abstract: T pitching moment coefficients in Ref. 1 are referred to an axis through the wing apex with the pitch axis through the quarter-chord point of the mean aerodynamic chord (MAC). It was the authors' intention to present the coefficients using the same reference and pitch axes at the quarterchord point of the MAC. The example wing had an aspect ratio of 8.0, a taper ratio of 0.25, a quarter-chord sweep of 30 deg., and was flying at a Mach number of 0.8. Using a new lattice idealization of the wing (since the original idealization was not recorded) defined by 5 equal chordwise divisions and 15 variable spanwise (narrower toward the tip) divisions, the new lift and corrected moment coefficients for the quarterchord MAC reference axis and pitch axis are presented in Table 1 for the nine values of reduced frequency previously considered. The calculations were based on the doublet-lattice method (DLM) of Ref. 2 as integrated into NASTRAN® and were carried out using MSC/NASTRAN; the original calculations were based on the DLM of Ref. 4 which was later developed into Ref. 5. Slight differences in the lift coefficients between the present and earlier solutions can be attributed to a different lattice idealization. If we extend Ref. 1 to permit different reference chords for reduced frequency (k = ub/V) and pitching moment coefficient

A comparison of computational models for fluid-structure interaction studies of flexible flapping wing systems

Abstract: In this article, the authors examine two computational approaches that can be used to study the motions of flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a problem of vortex kinematics, whereas with the DNS model, the focus is on forming a detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous eects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or constructing a predictive tool. In most of the cases studied in this work, the UVLM based approach produces a good approximation for CL/CD. Apart from comparisons of the aerodynamic loads, comparisons are also made of the features of the system dynamics generated by using the two computational approaches. Limitations of both approaches are also discussed.

Conceptual Design of a Bendable UAV Wing Considering Aerodynamic and Structural Performance

Abstract: A bendable UAV wing, developed at University of Florida, shows the ability to load stiffen in positive flight load direction, still remaining compliant in the opposite direction. Such a wing enables UAV storage inside smaller packing volumes. The present paper discusses utilization of a multidisciplinary design approach for conceptual design of a bendable wing having 24 inch span and 7 inch root chord. The wing shape definition parameters and the layup scheme used to manufacture wing, are treated as design variables. Aerodynamic performance of the wing is studied using an extended vortex lattice method based Athena Vortex Lattice (AVL) software. An arc length method based nonlinear FEA routine in ABAQUS is used to evaluate the structural performance of the wing and to determine maximum flying velocity that the wing can withstand without buckling or failing under flight loads. An analytical approach is used to study the stresses developed in the composite wing during storage and Tsai-Wu criterion is used to check failure of the wing due to the rolling stresses to determine minimum storage diameter. Multidisciplinary shape and layup optimization is performed using an elitist non-dominated sorting genetic algorithm: NSGA-II. The design points on the Pareto optimal front thus achieved are compared with a baseline design to observe some designs with improved performance. Important design variables are identified for further investigation.