Effects of Fuel Slosh on Flutter Prediction

The analysis of the sloshing effect of an internal fluid on a flutter envelope has received little attention, at least in the open literature. This problem can affect many aircraft, especially high performance fighter jets with wing-store configurations. This paper dis-cusses the modeling aspect of this problem and presents some computational results that quantify the effects of fuel slosh on the flutter characteristics of a test wing-store configura-tion. The geometry of the studied configuration is that of the AGARD Wing 445.6 with a blunt-nosed under-wing store. Fuel slosh is accounted for using a hydroelastic added mass model. Alternatively, the trivial representation of an internal fluid by mass lumping is also considered. Flutter calculations are performed using both approaches for accounting for the presence of an internal fluid and a validated CFD-based linearized method for solving fluid-structure interaction problems. It is found that for the considered wing-store system, ignoring the sloshing effect of an internal fluid by representing it as a lumped mass system overestimates the added mass effect, underestimates the critical pressure and flutter speed, and therefore leads to conservative conclusions. I.