POD(proper orthogonal decomplsition) 방법을 이용한 불안정한 프로펠러 후류 해석

Abstract

The complicated flow characteristics of upper propeller wake influenced by hull wake are investigated in detail in the present study. A two-frame PIV (particle image velocimetry) technique was employed to visualize the upper propeller wake region. As the upper hull wake affects strongly propeller inflow, upper propeller wake shows much unstable vortical behavior, especially in the tip vortices. Velocity field measurements were conducted in a cavitation tunnel with a simulated hull wake. Generally, the hull wake generated by the hull of a marine ship may cause different loading distributions on the propeller blade in both the upper and lower propeller planes. The unstable upper propeller wake caused by the ship’s hull is expressed in terms of turbulent kinetic energy (TKE) and is identified by using the proper orthogonal decomposition (POD) method to characterize the coherent flow structure in it. Instabilities appeared in the eigen modes higher than the second one, giving unsteadiness to the downstream flow characteristics. The first eigen mode would be useful to find out the tip vortex positions immersed in the unstable downstream region