# Cavitator Design for Straight-Running Supercavitating Torpedoes
###### Abstract  
A practical cavitator design method for straight-running-type supercavitating torpedoes was developed in this paper. Design requirements were first drawn in terms of torpedo performance characteristics, such as maximum range and motion stability. This method determines the optimum cavitator satisfying the design requirements that not only minimize the total drag of the torpedo, extending the maximum range, but also provide hydrodynamic forces required for straight level flight. The design procedure includes determining a design cavitation number and cavitator type (disk or cone) for obtaining the optimal cavitator that minimizes the total drag of a torpedo in straight level flight. To determine such an optimal cavitator, the equations of force and moment equilibrium for straight level flight were iteratively solved by the existing mathematical models that determine the cavity shapes generated by disk- and cone-shaped cavitators and hydrodynamic forces acting on the vehicle. For validation, model experiments on a small-scale supercavitating vehicle were conducted in a towing tank, and the results agree well with those of the mathematical models used in this study. A preliminary design based on the newly proposed method was also implemented for a realistic supercavitating vehicle. More precise computations using CFD should be conducted to investigate the physics in more detail in the near future. supercavitation; cavitator; supercavitating torpedo; cavitator design method 29 April 2021 1 July 2021 6 July  
The key technical areas for high-speed supercavitating torpedoes can be generally divided into cavitator, ventilation, guidance, control, and propulsion [4]. The detailed sub-technologies could be different depending on the operational concept of the torpedo: for example, an unguided straight-running torpedo such as Shkval or a guided homing torpedo such as Barracuda. This study mainly focuses on the cavitator design for a straight-running torpedo. A cavitator, mounted on the nose of the supercavitating torpedo, is required to initiate and maintain a supercavity with the aid of ventilation. However, because a cavitator is in continuous contact with water during supercavity generation, the hydrodynamic drag on the cavitator accounts for the largest portion of the overall drag of the torpedo and thus can significantly affect the torpedo performance, such as the maximum operating range. A cavitator is also closely associated with controlling the motion of the torpedo. As a supercavitating torpedo is unavoidably accompanied by negative buoyancy, the cavitator should produce sufficient hydrodynamic forces to compensate for the weight of the torpedo and stabilize the torpedo motion for underwater level flight [5; 6]. The cavitator design is crucial in developing a supercavitating torpedo because it is closely linked to the torpedo performance. The cavitator must be designed not only to create the supercavity required to minimize the overall drag of the torpedo in high-speed motion but also to provide the hydrodynamic forces required for straight and level flight while maintaining basic motion stability [6; 7]. Most previous works on cavitator design, however, focused only on shape optimization, in which drag is minimized without considering motion stability [8; 9; 10]. [PERSON] et al. [11] studied the optimal design of a supercavitating torpedo from a structural viewpoint and presented a method to determine the optimal configuration that satisfied the design requirements, in which the torpedo should operate inside the most stable portion of the cavity and be fitted in a torpedo tube. However, the hydrodynamic forces on the cavitator, required to stabilize the torpedo motion, were not explicitly considered in the design requirements.