Numerical Study on the Behavior of Air Layers Used for Drag Reduction

摘要

This contribution addresses achieving higher speed and higher propulsion efficiency by reducing drag of a hull. Placing an air layer beneath a hull to reduce the frictional resistance is a simple and attractive approach. However, one of the major issues of a practical air layer system is the stability of the air layer free surface with regards to the ship, motion and the upstream conditions. We address this issue of unsteady air layer behavior, using a boundary element method approach applied to the conditions of recent experiments with a large flat plate conducted in the Large Cavitation Channel. The numerical studies indicate that inclusion of small upstream unsteadiness is necessary to recover the experimentally observed air layer behavior and the critical air flow rates correctly. The numerical model is also applied to the unsteady excitation experiments conducted with imposed motion of a flapping gate.