Diagnostic-Photographic Determination of Drag/Lift/Torque Coefficients of High Speed Rigid Body in Water Column
NAVAL POSTGRADUATE SCHOOL MONTEREY CA NAVAL OCEAN ANALYSIS AND PREDICTION LAB
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Prediction of rigid body falling through water column with a high speed such as Mk-84 bomb needs formulas for draglift and torque coefficients, which depend on various physical processes such as supercavitation and bubbles. A diagnostic-photographic method is developed in this study to determine the draglift and torque coefficients for a fast moving rigid-body in water column. The diagnostic part is to derive the relationships called diagnostic relationships between drag, lift, torque coefficients and position, orientation of the rigid body from the three momentum equations and three moment of momentum equations. The photographic part is to collect data of trajectory and orientation of a fast moving rigid body using multiple high-speed video cameras 10,000 Hz. Substitution of the digital photographic data into the diagnostic relationships leads to semi-empirical formulas of draglift and torque coefficients, which are functions of the Reynolds number, attack angle, and rotation rate. This method was verified by 112th Mk-84 bomb strike experiment with various tail configurations tail section with four fins, two fins, and no fin and no tail section conducted at the SRI test site. The cost of this method is much lower than the traditional method using the wind tunnel. Various trajectory patterns are found for different tail configurations.
- Test Facilities, Equipment and Methods
- Fluid Mechanics