Showing papers on "Vortex lattice method published in 1978"

Subsonic Vortex-Flow Design Study for Slender Wings

Abstract: A theoretical study describing the effects of spanwise camber on the lift dependent drag of slender delta wings having leading-edge vortex flow is presented. The earlier work by Barsby, using conical flow, indicated that drag levels similar to those in attached flow could be obtained. This is re-examined and then extended to the more practical case of nonconical flow by application of the vortex-lattice method coupled with the suction analogy and the recently developed Boeing free-vortex-sheet method. Lastly, a design code is introduced which employs the suction analogy in an attempt to define "optimum" camber surfaces for minimum lift dependent drag for vortex flow conditions.

A theoretical investigation of the aerodynamics of low-aspect-ratio wings with partial leading-edge separation

Abstract: A numerical method is developed to predict distributed and total aerodynamic characteristics for low aspect-ratio wings with partial leading-edge separation. The flow is assumed to be steady and inviscid. The wing boundary condition is formulated by the quasi-vortex-lattice method. The leading-edge separated vortices are represented by discrete free vortex elements which are aligned with the local velocity vector at mid-points to satisfy the force free condition. The wake behind the trailing-edge is also force free. The flow tangency boundary condition is satisfied on the wing, including the leading- and trailing-edges. Comparison of the predicted results with complete leading-edge separation has shown reasonably good agreement. For cases with partial leading-edge separation, the lift is found to be highly nonlinear with angle of attack.

Development of a Viscous Vortex/Wing Interaction Program for Thick Wings with Rounded Leading Edge.

Abstract: : A hybrid viscous/potential flow program was developed to analyze the flow field on and around a swept thick wing with rounded leading edges and leading edge vortex flow. The program provides a computational package which includes four major programs run with proper interfacing in an iterative cycle. These programs include two viscous programs and two potential flow programs. The viscous flow programs consist of: (1) a parabolic solution to the Navier-Stokes vorticity equation in a box around the leading edge vortex; and (2) a three-dimensional second-order boundary layer program for infinite yawed wings. This program provides the boundary layer vorticity being fed into the vortex box. The two potential flow programs are: (1) the Hess surface singularity method for thick wings and fuselage combination; and (2) a vortex lattice method to model the leading edge vortex. These two programs provide the surface pressures and the viscous box boundary velocities. The program interfaces are developed by applying the concept to a 65 deg delta wing with a spanwise variation in leading edge radius. Operating experience is presented, giving the results and knowledge gained in each cycle of the iterations. The method allows the designer to design or modify the leading edge shape to meet the desired performance and control requirements.

A computer program for calculating aerodynamic characteristics of low aspect-ratio wings with partial leading-edge separation

Abstract: The necessary information for using a computer program to predict distributed and total aerodynamic characteristics for low aspect ratio wings with partial leading-edge separation is presented. The flow is assumed to be steady and inviscid. The wing boundary condition is formulated by the Quasi-Vortex-Lattice method. The leading edge separated vortices are represented by discrete free vortex elements which are aligned with the local velocity vector at midpoints to satisfy the force free condition. The wake behind the trailing edge is also force free. The flow tangency boundary condition is satisfied on the wing, including the leading and trailing edges. The program is restricted to delta wings with zero thickness and no camber. It is written in FORTRAN language and runs on CDC 6600 computer.