Development of Experimental Inversion and Simulation Techniques to Study Propeller Blade Response to Inflow Distortion.

Abstract : Marine propellers usually operate either in the non-uniform wake of a submarine or skewed flow under the stern of a surface ship. Therefore, the flow upstream of marine propeller blades is characterized by irregular patterns which are caused by various mean flow distortions due to the boundary layer growth on the hull of the ship, turbulent viscous wakes of upstream bodies (e.g., Hyun and Patel (1991)) or obstacles (e.g., Groves et al (1992)). Whether the inflow to the propeller is steady or unsteady, uniform or non-uniform, the flow over and downstream of the blades is unsteady. This unsteadiness can be due to a separation bubble near the leading edge of the blade, separated flow from the blade before the trailing edge, as well as tip and hub vortices. The unsteady flow over the blades produces unsteady hydrodynamic forces (i.e., excitations) which result in unwanted vibrations and noise. Inflow nonuniformities give rise to tonal and narrow band noise centered around the blade passing harmonics. Additional broad band signatures are superimposed due to turbulence-trailing edge interaction. Highly non-uniform and asymmetric inflows further exaggerate these effects. (MM)