Studies on the dynamics of a supercavitating projectile

Due to imperfect water entry, a high speed supercavitating projectile, whil e moving in the forward direction, rotates inside the cavity. This rotation leads to a series of impacts between the projectile tail and the cavity wa ll. The impacts affect the trajectory as well as the stability of motion of the projectile. The present paper discusses the in-flight dynamics of such a projectile. Equations of motion of the projectile are developed for two distinct phases of motion - Phase I: the projectile moves in the cavity wit hout interaction with the cavity wall, and Phase II: the tail impacts on th e cavity wall. The equations are found to be coupled and nonlinear. A simpl e model based on the concepts of flow planes is used to determine the force s acting on the projectile during impact. The effect of the mass distributi on on the projectile dynamics is also studied. The results show that despit e the impacts with the cavity wall, the projectile nearly follows a straigh t line path. The frequency of the impacts between the projectile tail and c avity boundary increases initially, reaches a maximum, and then decreases g radually. The results also indicate that the frequency of impacts decreases with the projectile's moment of inertia. It is also shown that the impact of the projectile with the cavity wall can be modelled as an impact with a rigid barrier with variable coefficient of restitution. A functional form o f the coefficient of restitution is proposed, and it is shown that the prop osed form predicts the impact behaviour quite well. (C) 2000 Elsevier Scien ce Inc. All rights reserved.