Modeling of Contra-Rotating and Ducted Propellers via Coupling of a Vortex-Lattice with a Finite Volume Method

Abstract

This paper describes a general numerical method of analyzing propeller hydrodynamic performance, with emphasis on contra-rotating (CRP) and ducted propellers. The main difficulty in this analysis is the complexity of the interaction between the two blade rows, in the case of a CRP, and between the propeller and the surrounding duct, in the case of a ducted propeller. The current method couples a Vortex-Lattice Method (VIM) applied to each of the blade rows of the CRP or the propeller inside the duct, with a Finite Volume Method (FVM) based Euler solver applied to the global flow-field, in order to account for the interactions mentioned above. The VIM solver (MPUF-3A) solves for the potential flow in the vicinity of the propeller and predicts the pressures, forces and moments, and cavity patterns on the blades. The FVM solver (GBFLOW-3X/3D) converts the pressure forces on the blades to body forces inside the flow domain and then solves the Euler equations with respect to the total velocity field and pressure. By subtracting the propeller-induced velocities, from the total flow, the "effective wake" is determined. For CRPs, the "effective wake" for each blade row includes the interaction with the other blade row. For ducted propellers, the "effective wake" includes the interaction with the duct. The "effective wake" is then provided to the VIM solver for a new round of body force computation. This iterative process between the VIM and the FVM is repeated until convergence. Several validations of results from the current numerical method with those of other computational methods and with those measured in experiments are presented.