ABSTRACT of the Doctoral Thesis

Membrane Wings in Unsteady Potential Flow

(Membrantragflächen in instationärer Potentialströmung)

by Nikolaus Friedl (2002)

In this work a method will be described, which allows the simulation of membrane wings in unsteady potential flow. Typical examples for membrane wings are hang-gliders, kites and sails of boats. In the case of hang-gliders the wing has very little torsional stiffness. The wing shape, i.e. the angle of attack along the wingspan, is governed by both the nonlinear membrane structure and the aerodynamic loads, which in turn depend on the geometry of the structure. Therefore this system is dominated by strong fluid-structure interaction.

The first part describes the development of a novel higher order vorticity panel procedure for solving the unsteady potential flow problem. The procedure uses the same mesh as the nonlinear Finite Element code, which has advantages with respect to the coupling schemes. Beside aerodynamic loads the fluid module also calculates the load derivates with respect to displacements and velocities. This feature allows the simultaneous solution of the coupled unsteady problem.

The second part deals with the structural problem, introducing special Finite Elements and procedures for the simulation of membrane wings.

The third part shows different coupling schemes for the stationary problem. The simultaneous scheme is then extended to unsteady problems.

The last chapter describes the model and flight tests of an hang-glider in unsteady motion.

revised 021010 (hjb)