Ducted Propeller Flow Analysis by Means of a Generalized Actuator Disk Model

Abstract

The paper presents a generalized semi-analytical actuator disk model as applied to the analysis of the flow around ducted propellers at different operating conditions. The model strongly couples the non-linear actuator disk method of Conway[1] (J. Fluid Mech. 1998; 365: 235-267) and the vortex element method of Martensen[2] (Arch. Rat. Mech. 1959; 3: 235-270) and it returns the exact solution, although in an implicit formulation, for incompressible, axisymmetric and inviscid flows. The solution is made explicit through a semi-analytical procedure developed and validated by Bontempo and Manna[3] (J. Fluid Mech. 2013;728:163-195). Moreover the method duly accounts for non-uniform load radial distribution, slipstream contraction, mutual non-linear interaction between duct and propeller, wake rotation, and ducts of general shape. Thanks to its extremely reduced computational cost it can easily be integrated into design systems based on the repeated analysis scheme of hierarchical type. A comparison between open and ducted rotors is carried out in order to quantify the effects of the duct on the overall performance of the device. Emphasis is given to the appropriate matching between the duct geometry and the propeller load to exploit the benefits that could arise ducting the propeller.