The effect of an upstream hull on a propeller in reverse rotation

Abstract

AbstractPropeller crashback is an off-design operating condition where a propeller rotates in the reverse direction. Experiments (Bridges 2004,Tech Rep.MSSU-ASE-04-1, Department of Aerospace Engineering, Mississippi State University) have shown that the presence of an upstream hull significantly increases the side force on a propeller in crashback below an advance ratio of$J= \ensuremath{-} 0. 7$. Large-eddy simulation (LES) is performed for a propeller with and without a hull at two advance ratios,$J= \ensuremath{-} 1. 0$and$J= \ensuremath{-} 0. 5$. LES reproduces the experimentally observed behaviour and shows good quantitative agreement. Time-averaged flow fields are investigated for a qualitative understanding of the complex flow resulting from the interaction of the upstream hull with the propeller blades. At$J= \ensuremath{-} 1. 0$, two noticeable flow features are found for the case with the hull – a recirculation zone upstream in the vicinity of the propeller and a vortex ring much closer to the propeller. In contrast, at$J= \ensuremath{-} 0. 5$, there is a much smaller recirculation zone which is further upstream due to the increased reverse flow. As a result, the hull does not make much difference in the immediate vicinity of the propeller at$J= \ensuremath{-} 0. 5$. For both advance ratios, side force is mainly generated from the leading-edge separation on the suction side. However, high levels of side force are also generated from trailing-edge separation on the suction side at$J= \ensuremath{-} 1. 0$.