Showing papers on "Vortex lattice method published in 1992"

Extension and validation of an unsteady wake model for rotors

Abstract: A new three-dimensional, finite-state induced-flow model is extended to treat nonlinearities associated with the mass flow induced through the rotor plane. This new theory is then applied to the correlation of a recent set of unsteady, hover laser Doppler velocimetry inflow measurements conducted in the Aeroelastic Rotor Test Chamber at Georgia Institute of Technology. Although the model is intended primarily as a representation of unsteady aerodynamics for aeroelasticity applications, the results show that it has an excellent capability in predicting the inflow distribution in hover except near the root and tip. In addition, the computed unsteady spanwise lift distribution of a rotor is compared with that from an unsteady vortex lattice method for pitch oscillations at various frequencies. The new model is shown to be capable of prediction of unsteady loads typical of aeroelastic response.

Effect of canard deflection on close-coupled canard-wing-body aerodynamics

Abstract: The thin-layer Navier-Stokes equations are solved for the flow about a canard-wing-body configuration at transonic Mach numbers of 0.85 and 0.90, angles of attack from -4 to 10 degrees and canard deflection angles from -10 to +10 degrees. Effects of canard deflection on aerodynamic performance, including canard-wing vortex interaction, are investigated. Comparisons with experimental measurements of surface pressures, lift, drag and pitching moments are made to verify the accuracy of the computations. The results of the study show that the deflected canard downwash not only influences the formation of the wing leading-edge vortex, but can cause the formation of an unfavorable vortex on the wing lower surface as well.

Calculation of Blade-Vortex Interaction of Rotary Wings in Incompressible Flow by an Unsteady Vortex-Lattice Method Including Free Wake Analysis

Abstract: A vortex-lattice method is presented that allows the calculation of the flow around n-bladed rotor configurations using a time-dependant wake-shedding procedure. Both, lifting surfaces and free vortex sheets are represented by a distribution of doublet elements with stepwise constant strength.

Numerical analysis of unsteady open water characteristics of marine propellers by surface vortex lattice method

Abstract: In this paper, the applications of surface vortex lattice method to marine propellers in non-uniform flow are considered.The surface vortex lattice method based on the general vortex lattice method is possible to simulate the flow around a lifting body including thickness and volume effects by distributing horse-shoe vortices and surface source distributions on the both side surfaces of the blades. The advantage of this method compared to other panel methods is the fact that the Kutta-condition is satisfied automatically in not only steady condition but also unsteady condition by convecting the trailing and the shed vortices. The geometry of the wake using the linear wake model having the geometrical pitch of blades and all shed vortices are convected to new positions step by step with a small time interval.Three propellers are used to confirm the accuracy of the results of the present method. At first, the fluctuation of the thrust and the torque coefficients of a propeller in harmonic wake are calculated to compare the time derivative term with the results by VLM. And next, the pressure distribution on the blade concerning to two full scale propellers are calculated by the present method.The results of these calculations are good agreements with experimental results and other theoretical calculations

Generalized vortex lattice method for oscillating lifting surfaces in subsonic flow

Abstract: A numerical method for calculating the unsteady pressure distribution on harmonically oscillating lifting surfaces in subsonic flow is presented. The Helmholtz equation for the complex velocity potential is written in integral form and solved by discrete panels superposition, which can be recognized as a generalization of the well-known vortex lattice method. Numerical calculations are carried out for a rectangular wing and are compared with well-established literature data. The influence of chordwise and spanwise discretization, as well as wake length, on the convergence rate, is also numerically studied

Aerodynamic Characteristics of Elastically Deformed 3-Dimensional Membrane Sail

Abstract: It is well known that aerodynamic forces acting on an elastic lifting surface are affected by structural deformations caused by aerodynamic forces on the surface or changes of attack angle due to these deformations. This type of problems are referred to as aeroelastic problems. Aeroelastic effects are much more significant in aerodynamic performance of yacht sails than ordinary wings of aircrafts, because the sail of yacht is formed by an elastic membrane. The pressure distribution on a membrane in a flow can be calculated if the shape of the membrane is determined. However, the shape is a result from the equilibrium of aerodynamic pressure and inner stress of the membrane, which depends on aerodynamic pressure. In order to treat this kind of mutual interaction between aerodynamic forces and elastic forces, some analytical or numerical approaches have been proposed to give reasonable solutions.In the present paper, Finite Element Method and a modified Vortex Lattice Method are adopted to solve aeroelastic problems of 3-dimensional elastic membrane sails. Made is use of large deformation incremental method to calculate stress and strain in deformed state of membranes, and to determine the sail shape in equilibrium state under loadings. One of the main advantages of the incremental method is that this method can be applied to dynamic problems more easily than the iterative method.The usefulness of this approach is confirmed by comparing numerical results obtained by the present method with existing numerical solutions of elastic membranes and experimental results of yacht sails as well. As examples of application of the solution proposed in this paper, a series of numerical calculation is carried out to clarify the effect of leech tension and sail material on the aerodynamic performance of sail.

Numerical simulations of flutter and its suppression by active control

Abstract: A method for predicting the unsteady, subsonic, aeroservoelastic response of a wing has been developed. All equations are solved simultaneously in the time domain by an iterative scheme based on a predictor-corrector method. The scheme allows a wide range of nonlinear aerodynamic and structural models to be used and subcritical, critical, and supercritical aeroelastic behavior can be modeled without restrictions to small disturbances or periodic motions. A general vortex lattice method is used to model the aerodynamics

Analysis of wings with spanwise multi-segmented flaps

Abstract: A vortex lattice method has been developed to analyse simple, swept, tapered wings with spanta ise segmented flaps at both leading and trailing edges . Classical planar horse shoe vortex is used as the basic solution to the governing Laplace's equation . Compressibility corrections (ire accounted for using Prandil-Glauert analogy modified as applicable to wins with deflected flaps. Extensive numerical experimentation has been carried to detcrinine the optin/um lattice layout. The method has been validated using a number of test cases available in published literature