Hydrodynamically Streamlined, Pressure Resistant, Hollow Strut for Underwater Service

摘要

Hydrodynamically streamlined struts in the shape of airfoils present less drag than cylindrical pipes and are thus more desirable for underwater applications where the current velocity is significant and the drag on the structure is to be minimized. The foil shape, however, does not lend itself readily to calculation of stresses induced by external pressure and/or hydrodynamic forces in the form of drag and lift. This paper summarizes the experimental evaluation of NACA -0021 airfoil adapted by NOSC for underwater service as a pressure-resistant strut on underwater vehicles. The author includes: 1) The NACA 0021 foil, has been found to perform satisfactorily as an external pressure vessel capable of withstanding high flexure ad torque moments generated by hydrodynamic drag and lift of water rapidly floating over the surface of the foil; and 2) Cast Ti-6A1-4Va alloy is a cost effective material for fabrication of streamlined, external pressure resistant, hollow struts. The 2.38 weight to displacement ratio of the cast titanium hollow strut makes it an acceptable structural component for weight limited underwater vehicles. Keywords: Static drag; Cross flow oscillations; Hydraulic turbine.