Water Entry Study of the MK 25 Torpedo with 3.5-Calibre 70-Degree Spherogive Head

Abstract

This report describes a study conducted jointly by the Hydrodynamics Laboratory of the California Institute of Technology and the Pasadena Annex of the Naval Ordnance Test Station, Inyokern. Air to water launchings were made with a full-size (22.42-in. dia.) dummy Mk 25 aircraft torpedo with a 3-l/2-cal. 70° spherogive nose and with a 2-in. dia. model of the same shape. The purpose of this investigation was to study the problems associated with water entry modeling. Froude scaling was used to determine model entry velocity and the air pressure in the model system was reduced until the cavitation number of the model equaled that of the prototype. Equal cavitation number and equal Froude number scaling was found to be adequate as long as a turbulent boundary layer existed in the flow around the model. When the entry velocity of the model was low enough for a laminar boundary layer to occur, the trajectory of the model deviated from that of the prototype beyond 35 diameters of underwater travel. It was then necessary to induce turbulence in the boundary layer by roughening the nose of the model before successful modeling could be achieved. The tests made during this investigation were with the following entry conditions: Entry Velocity prototype - 200 fps and 400 fps model - 60, 80 and 120 fps Air Pressure prototype - l atm. model - l, 1/ll and l/21 atm. Air Trajectory prototype and model - 22° Entry Pitch Angle prototype - 0 to 6° nose up model - 3° nose down to 6° nose up