A Detailed Study of the Flow Field of a Submarine at Large Angle of Drift
Abstract
When a submarine executes a high-speed turn, the sail experiences a cross-flow velocity component. Because the sail is essentially a low-aspect-ratio finite-span wing, it sheds a tip vortex. The flow field induced by the vortex causes higher pressures on the hull deck and lower pressures on the keel, creating a net downward force that leads to an uncommanded nose-up pitching moment. Tests to examine the features of such flows were conducted in the U. S. Navy's Large Cavitation Channel (LCC) in Memphis, TN. A submarine model of length 22.7 ft was mounted in the LCC at angles of drift of 0, 5, and 9.5 degrees and was tested with the sail on and off. Tests were conducted at speeds up to 14.9 m/s (27-kts). Circumferential pressure distributions and laser Doppler velocimeter (LDV) surveys were obtained at two axial locations for each of the speeds and configurations tested. Body forces and moments were also measured using a 6-component force balance. The pressure distributions were integrated to obtain section vertical force coefficients, and the velocity data obtained from the LDV measurements were used to estimate the circulation of the tip vortex. The measured pressure distributions were consistent with the hypothesized mechanism by which the tip vortex changed the flow around the submarine and created the nose-up pitching moment. The measured pitching moment and the sectional vertical force coefficients demonstrated the nonlinear variation with angle of drift predicted by theory. The measured values of the circulation were in general agreement with values obtained by other researchers, although the measured circulation values were consistently somewhat higher.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2001
- Accession Number
- ADA390797
Entities
People
- David H. Bridges
Organizations
- Mississippi State University