Effect of Fuel Sloshing in the External Tank on the Flutter of Subsonic Wings

Abstract

This study considers the aeroelastic instability of a subsonic wing with an external fuel tank store containing sloshing fuel. The wing is modeled using Euler-Bernoulli beam and the fuel sloshing is simulated by a mass-spring-damper system as an equivalent mechanical model. An extension of the Peters finite-state aerodynamic model along with the strip theory is utilized to obtain the external work due to the unsteady lift and pitching moment. Also, the aerodynamic loads on the store are calculated using the slender body theory. Using Lagrange equations, the governing equations of motion are derived and solved by the Rayleigh-Ritz method to determine the flutter speed of the wing/store. The effect of fuel sloshing on the aeroelastic instability of the wing is investigated by several numerical studies and some conclusions are outlined. The obtained results show that when the fuel-sloshing frequency in the external tank is between the frequencies of the fundamental bending and torsional modes of the wing, the sloshing/aeroelasticity coupling occurs. Numerical studies illustrate that the fundamental frequency and damping of sloshing in the tank are the main parameters determining the increase or decrease of the flutter speed and a proper tuning of these parameters can considerably extend the flutter-safe speed range.