Study of Wing Flutter at Preliminary Stages of Design

Abstract

Study of problems associated with aircraft flutter requires understanding of aerodynamics and structural dynamics. As the aircraft speed increases, the energy coming to structure causes the wing to deflect and in turn the deflection is in such way that it adds energy back to the structure. The positive coupling between wing deflection and aerodynamic forces enables self-sustained oscillation, which is generally referred as flutter, and it can cause structural failure. A simple spring mass system for vibration with external source describes the basic phenomena. Linear model of the problem was well studied by various authors. With the current capabilities of MATLAB/Simulink, it is possible to visualize the oscillations. The problem was simulated in the previous study and verified with available data in the literature. In the present study, the mass, moment of inertia and spring stiffness in heave and pitch motions have been varied. A 5% reduction in mass from the baseline mass 51.5 kg reduces the flutter speed of 1 m/s from the baseline speed 188.65 m/s. The basic premise is to shift the flutter speed upward and beyond the aircraft flight envelope. This will minimize the probability of aircraft entering into flutter. A surrogate meta-model is developed based on Kriging method. Genetic algorithm is used on the meta-model to optimize the design variables. The optimum value of flutter speed in the given range of design variables is about 7.4 m/s more than the baseline case. This study describes a systematic approach on implementation of multidisciplinary design optimization on a simple problem.