INTERFERENCE BETWEEN A HULL AND A STERNMOUNTED DUCTED PROPELLER.
Technical rept. 1 Oct 64-30 Sep 65,
VIDYA DIV ITEK CORP PALO ALTO CALIF
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A hydrodynamic analysis was made of an underwater hull and a stern-mounted ducted propeller in steady axially symmetric flow. Singularity distributions are used to represent a typical hull, the hull wake, a thin cambered duct, and the propeller. The propeller is approximated by an actuator disk which adds a uniform velocity to the slipstream. Duct camber lines are chosen to minimize duct leading-edge suction, the hull-duct interference force, and separation of the duct boundary layer. The potential flow field, duct boundary layer, and interference forces are all predicted versus duct length, duct thrust, duct loading distribution, and Reynolds number. As an aid in the design or selection of an experimental propeller, its inflow, loading, and power are estimated. For the assumed conditions, the computed results show that a long duct with chord equal to exit diameter can finally provide only about 7 percent as much net thrust as the propeller before the boundary layer separates from the outer duct surface. One reason for this low value is that about half the duct thrust is lost to duct shear drag. A duct half as long can provide only 6 percent as much net thrust as the propeller before separating. Increasing the Reynolds number based on duct chord from 2,400,000 to 3.2x10 to the 7th power allows only a small increase in duct thrust before separation. It is concluded that relatively little thrust can be carried by ducts of the assumed type without boundary-layer control to delay separation. Author
- Marine Engineering
- Fluid Mechanics