Showing papers on "Vortex lattice method published in 1988"

A multi-element vortex lattice method for calculating the geometry and effects of a helicopter rotor wake in forward flight

Abstract: A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.

Analysis of wing flap configurations by a nonplanar vortex lattice method

Abstract: A nonplanar vortex lattice method is described for calculating the potential flow aerodynamic characteristics of complex planforms, with an emphasis on wings with spanwise segmented partial-span flaps. A new technique has been developed for proper modeling of flow in the region between the flap edges and the wing in the case of part-span flaps. The effects of compressibility have been accounted for by the use of the Prandtl-Glauert rule with no approximation being made regarding freestream incidence, wing camber, and flap deflection. The method has been tested for a number of cases to assess its utility.

Computational and experimental investigations of the flow around cavitating hydrofoils

Abstract: The linearized boundary value problem of the two dimensional cavitating hydrofoil of general shape has been solved semi-analytically by inversion of the singular integral equations describing the unknown source and vortex distributions and the subsequent numerical integration over such known functions as the slope of the wetted foil surface. However, a more desirable method of solution is one which permits a natural extension to the solution of three dimensional wing and propeller cavitation. The method of discrete singularities, which has the advantage of being the two dimensional analog of the vortex lattice method, has been studied extensively for this reason. The current research included the extension of the method to solve the the most general problems of partial and supercavitation with the correct points of cavity detachment and the most physically acceptable closure model. The results of an experiment in the MHL water tunnel show good agreement with numerical results. The correlation between numerical and experimental cavitation numbers, along with the latest extensions to the analysis, is presented. Aknowledgements I would like to acknowledge the continuous and invaluable aid and advice provided by Dr. Spyros Kinnas during all phases of this research. In particular, his contributions to the analysis of face cavitation and midchord detachment were significant. The support, technical and otherwise, of Professor J.E. Kerwin and the rest of the propeller group is gratefully acknowledged. Finally, in the preparation of this document, the tedious job of proofing went to the dynamic tandem of Kelly Morris and Andrea Novacky. Without their intelligent suggestions, I would be much less satisfied. This research was sponsored in part by the Naval Sea Systems Command General Hydromechanics Research Program administered by the David W. Taylor Naval Ship Research and Development center, and in part by the Volvo Penta Corporation.

A vortex-lattice method for the calculation of wing-vortex interaction in subsonic flow

Abstract: Flow interferences between wings and free vortex sheets (e.g. canard-wing with vortex separation) can influence the aerodynamic characteristics of a configuration to a considerable extent. If viscous and turbulent effects are negligible, potential flow methods represent a suitable way to calculate wing-vortex interactions and in many cases lead to simpler mathematical structures than Euler methods.

Calculation of the hydrodynamic forces acting on a hydrofoil

Abstract: Characteristics of a hydrofoil have been treated using the lifting surface theory or the vortex lattice method and the wavemaking resistance theory, which need very complicated calculations. But these methods can not directly predict the pressure distribution on the hydrofoil with thickness. This paper presents a method to calculate the flow around the hydrofoil and the hydrodynamic forces acting on the hydrofoil using the thick wing theory and the Rankine source method. Thick wing is represented by the source distribution on the hydrofoil and the vortex distribution on the chord. The strength of these singularities are obtained from the boundary condition on the hydrofoil and the Kutta's condition. In order to represent the wave flow, the source distribution is set on the still water surface so as to satisfy the Dawson's double-model linearised free surface condition. Since the flow field is calculated using these singularities, the pressure distribution, the lift and drag on the hydrofoil are obtained easily. As the numerical examples, we show the wave profiles or the wave contours, the pressure distributions and comparison of the lift and drag coefficients of the 2-D hydrofoils (NACA 0009 and NACA 0012) and the 3-D hydrofoils (NACA 64, A 412, Aspect Ratios of 4 and 10) between calculated and experimental results.

Vortical Wakes Over a Prolate Spheroid

Abstract: The vortex-lattice method is employed to calculate the inviscid flow and the development of separated vortex sheets over a prolate spheroid. An approximate boundary-layer method based on the assumption of local similarity is used to calculate the line of open separation. A condition of vortex shedding along the separation line is proposed. The two methods of calculation, viscous and inviscid, interact through the line of separation that is allowed to displace as the wake grows. Results are compared with flow visualization data for laminar separation and pressure data for turbulent separation.