Showing papers on "Vortex lattice method published in 2000"

Force and Power Estimation in Fish-Like Locomotion Using a Vortex-Lattice Method

Abstract: The forces and power needed for propelling at constant speed an actively swimming flexible fish-like body are calculated. A vortex-lattice method based on a linearized theory is employed and the results are compared against slender body theory predictions, as well as experimental data from an eight-link robotic instrument, the RoboTuna. Qualitative agreement is found between our method and slender body theory; with quantitative agreement over certain parametric ranges and disagreement for other ranges of practical interest

Approximate Added-Mass Method for Estimating Induced Power for Flapping Flight

Abstract: A method that uses the added mass of vortex sheets was developed to estimate induced power in e apping e ight for birds and insects. This new method has advantages over existing methods. First, it is valid for e ights with any forward velocity. Second, this method can be used to determine the effects of most kinematic parameters of e apping wings on induced power, like the inclination of the stroke plane, amplitude of the e apping angle, and the mean e apping angle. For hovering e ight this method has the same accuracy as methods based on the Rankine ‐ Froude momentum theory or on vortex ring theory. When the forward velocity is large, this method agrees with the momentum theory for a e xed wing.

Model Validation of Wake-Vortex / Aircraft Encounters

Abstract: Wake-vortex effects on an 10% scale model of the B737-100 aircraft are calculated using both strip theory and vortex-lattice methods. The results are then compared to data taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). The accuracy of the models for a reduced geometry, such with the horizontal stabilizer and the vertical tail removed, is also investigated. Using a 10% error in the circulation strength and comparing the model's results with the experiment illustrates the sensitivity of the models to the vortex circulation strength. It was determined that both strip theory and the vortex lattice method give accurate results when all the geometrical information is used. When the horizontal stabilizer and vertical tail were removed there were difficulties modeling the sideforce coefficient and pitching moment. With the removal of only the vertical tail unacceptable errors occurred when modeling the sideforce coefficient and yawing moment. Lift could not be accurately modeled with either the full geometry or the reduced geometry.

Flexible Wing Model for Structural Sizing and Multidisciplinary Design Optimization of a Strut-Braced Wing

Abstract: This paper describes a structural and aeroelastic model for wing sizing and weight calculation of a strut-braced wing. The wing weight is calculated using a newly developed structural weight analysis module considering the special nature of strut-braced wings. A specially developed aeroelastic model enables one to consider wing flexibility and spanload redistribution during in-flight maneuvers. The structural model uses a hexagonal wing-box featuring skin panels, stringers, and spar caps, whereas the aerodynamics part employs a linearized transonic vortex lattice method. Thus, the wing weight may be calculated from the rigid or flexible wing spanload. The calculations reveal the significant influence of the strut on the bending material weight of the wing. The use of a strut enables one to design a wing with thin airfoils without weight penalty. The strut also influences wing spanload and deformations. Weight savings are not only possible by calculation and iterative resizing of the wing structure according to the actual design loads. Moreover, as an advantage over the cantilever wing, employment of the strut twist moment for further load alleviation leads to increased savings in structural weight.

Numerical Simulation of Rotor Flow in Hover

Abstract: O calculate the aerodynamic performance of a helicopter in hovering e ight is a problem of great practical importance as well as the theoretical complexity. Theoretically, a solution of the fullNavier‐Stokes equations with appropriate turbulence modeling and body-conforming grid is sufe cient for a good description of all ofthephysicsinvolved.Butunlikethee owe eldaroundae xedwing, the trailing vortex wake of a rotary wing rotates with the rotor and is shed to a far distance below the rotor plane by its self-induced velocity. The helical vortex sheet interacts strongly with the lifting surfaces, but this process is hard to be simulated unless using a quite clustered grid, which generally requires very large computational resource. Srinivasan et al., 1 using about one million grid number to solve the thin-layer Navier ‐Stokes equations, calculated the whole e owe eld including the induced effects of the wake and the interaction of tip vortices with successive blades, but they also found their captured vortex structure was overdiffused because of the coarse grid used. The current methods for calculating rotor performance usually solve the potential, Euler, or Navier ‐Stokes equations coupled with anexternalfree-orrigid-wakemodelbasedonthe liftlineorliftsurfacetheory. 2i 6 Butitis clearthatthese governing equations arehard to match with the linear trailing wake modeling in a physically consistent manner. Further, those approaches also require fairly large computer resource from solving two coupled models simultaneously. Agarwal andDeese 7 calculatedthe aerodynamic loadsby solving the thin-layer Navier ‐Stokes equations, and the rotor-wake effects were modeled with a correction applied to the geometric angle of attack along the blades. This correction was obtained by computing the local induced downwash by the rotor wake with a free-wake analysis program. In fact, this method just established a weaker link between the rotor and its wake and avoided the complex boundary handling and the solution of coupled equations. Therefore, the grid number used is not huge, and the accuracy of calculated results is satisfactory. In the present paper we essentially borrowed the approach from Ref. 7, but extended it to the solution of a complete Navier ‐Stokes equation, rather than a thin-layer one. In addition, an improved method is suggested to obtain a proper correction of the local angle of attack of the blades. This is constructed by the comparison between the results with and without rotor wake modeling, in addition to a heuristic consideration of the coupling rotor-wake and threedimensional blade-tip effects that is expressed by a semi-empirical

The vortex lattice method in the spectral problem of a rectangular waveguide with a lamellar grating

Abstract: Interest in research and use of slowing-down electromagnetic systems in waveguides with rectangular grooves has recently been revived. In the present work, a rigorous solution to the spectral problem of an infinite rectangular waveguide for the longitudinal electrical waves with periodic slowing-down systems, with any number of arbitrary size resonators in the period, is considered. This work is a generalization of previous results, where we considered a lamellar grating with one resonator in the period by using the discrete singularities (currents) method, also known as the vortex lattice method.