Numerical simulations of waterjet inlets have been conducted in order to understand inlet performance during ship turning maneuvers. During turning maneuvers waterjet systems may experience low efficiency, cavitation, vibration, and noise. This study found that during turns less energy arrived at the waterjet pump relative to operating straight ahead, and that the flow field at the entrance of the waterjet pump exhibited a region of both low pressure and low axial velocity. The primary reason for the change in pump inflow uniformity is due to a streamwise vortex. In oblique inflow the hull boundary layer separates when entering the inlet and wraps up forming the streamwise vortex. These changes in pump inflow during turning maneuvers will result in increased unsteady loading of the pump rotor and early onset of pump rotor cavitation.
Simulations covered drift angles from 0° to 30°, pump velocities relative to free stream speed of 0.6 to 1.0 for inlet geometries with ramp angles of 25° and 30° with inlet-hull fairing radii relative to pump diameter of 0.1 to 0.2. The following observations were made: 1) the onset of the streamwise vortex occurred between drift angles of 5° and 10°; 2) increasing drift angle increased the strength of the streamwise vortex and lowered the energy of the flow entering the pump; 3) increasing the flow rate through the waterjet system increased the strength of the streamwise vortex; 4) increasing ramp angle tended to increase the strength of the streamwise vortex; and 5) increasing the fillet radius decreases the strength of the streamwise vortex.
Simulations of steady ahead operation of the waterjet propelled R.V. Athena were also conducted for Froude numbers of 0.34 to 0.84. From these simulations it was found that the pump inflow can be effectively approximated at a new ship speed from a known ship speed by scaling only the mean component of the axial velocity by the relative change in waterjet flow rate. Additionally, waterjet pump operating point and rotor blade inflow angles were found to independent of ship speed.
|Advisor:||von Ellenrieder, Karl|
|School:||Florida Atlantic University|
|School Location:||United States -- Florida|
|Source:||DAI-B 77/08(E), Dissertation Abstracts International|
|Subjects:||Naval engineering, Ocean engineering|
|Keywords:||Inlet, Maneuvering, Propulsion, Waterjet|
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