Causes and Corrections for Propeller-Excited Airborne Noise on a Naval Auxiliary Oiler

摘要

The AO-177, first of a new class of Naval Auxiliary Oilers, experienced high levels of inboard airborne noise and initial-stage erosion damage on its skewed, seven-bladed propeller during builder's trails. This report describes the problems, corrective design modifications considered, and procedures and rationale used to develop a successful corrective design modification consisting of a fin to improve the flow into the propeller. To evaluate the problem, extensive model experiments were conducted, including flow visualization, wake survey, powering experiments, and a crucial series of cavitation experiments including propeller-induced hull pressure measurements in a large water tunnel. Experiments with two fin designs showed the superiority of a flow-accelerating configuration. Other experiments showed some benefits of altering the propeller blade shape. Propeller analyses were undertaken to provide design alternatives for retrofitting the ship with a new propeller. A full-scale trail with the final fin design provided evidence or reduction of the highest levels of airborne noise, reduction in the initial-stage erosion damage, and minimal effect on ship speed. The result is that the AO-177 has been accepted by the fleet for normal service. (Author)