Unsteady Force and Moment Measurements on a Non-Body of Revolution Vehicle Undergoing Oscillatory Roll

Abstract

The aerodynamic forces and moments on a non-body of revolution ellipsoidal model in oscillating roll are studied. The model is mounted to the new Model Roll Oscillator in the Virginia Tech Stability Wind Tunnel fitted with its slotted wall test section. Three loadcells are mounted to the inside of the model and sting support. The roll oscillator is capable of positioning the model at yaw or pitch angles between ±15°. In roll, the oscillator is capable of maintaining static angles between ±26° as well as performing dynamic roll with a maximum speed of 5 Hz. Steady force and moment data are taken at yaw angles of -5°, -10°, and -15° with a sweep of roll angles between 25° and -10°. Unsteady forces and moments are presented for a -15° yaw turn) with a 3.25 Hz roll oscillation between ±26°. The study is performed to simulate the observed behavior of another non-body of revolution submarine model during underwater free-running yawing maneuvers, with similar non-dimensional roll oscillation speed. The study contributes to the understanding the forces and moments experienced by non-body of revolution vehicles in periodic roll, for which there is no existing data. The study determines a functional form for the steady forces on a non-body of revolution vehicle in coupled yaw and roll. Furthermore, this study quantitatively demonstrates the dynamic roll instability of non-bodies of revolution in constant-yaw turns. The roll moment, of particular interest, exhibits an unstable linear dependence on roll angle, indicating static roll instability. Unsteady results indicate that the roll moment in fact leads the quasi-steady data, causing a destabilization which can lead to an oscillatory rolling motion.