Analysis of the flow field around a rudder in the wake of a simplified marine propeller

Abstract

The vortex–body interaction problem, which characterizes the flow field of a rudder placed downstream of a single-blade marine rotor, is investigated by numerical simulations. The particular topology of the propeller wake, consisting of a helicoidal vortex detached from the blade tips (tip vortex) and a longitudinal, streamwise oriented vortex originating at the hub (hub vortex), embraces two representative mechanisms of vortex–body collisions: the tip vortices impact almost orthogonally to the mean plane, whereas the hub vortex travels in the mean plane of the wing (rudder), perpendicularly to its leading edge. The two vortices evolve independently only during the approaching and collision phases. The passage along the body is instead characterized by strong interaction with the boundary layer on the rudder and is followed by reconnection and merging in the middle and far wake. The features of the wake were investigated by the $\unicode[STIX]{x1D706}_{2}$-criterion (Jeong & Hussain, J. Fluid Mech., vol. 285, 1995, pp. 69–94) and typical flow variables (pressure, velocity and vorticity) of the instantaneous flow field; wall pressure spectra were analysed and related to the tip and hub vortices evolution, revealing a non-obvious behaviour of the loading on the rudder that can be related to undesired unsteady loads.

Underlying mechanisms of propeller wake interaction with a wing

“…A three-dimensional reconstruction of the vortex reconnection mechanism after its penetration into the wing is shown in figure 29, which reports the propeller phase-locked iso-surfaces of the vorticity magnitude measured by LDV for J = 0.88. This result is in agreement with previous works about the crucial role of the boundary layer in the recovery mechanism of the incident vortex after penetration (see, e.g., Liu & Marshall 2004;Muscari et al 2017). x + ω 2 y + ω 2 z in the rotational upper region of the rotor.…”

“…The propeller was a reference propeller model, namely the INSEAN E779a propeller (figure 1). This propeller, widely studied by earlier wake surveys (see, e.g., Cenedese, Accardo & Milone 1985;Felli et al 2006Felli et al , 2009Felli, Grizzi & Falchi 2014;Muscari et al 2017;Felli & Falchi 2018), is a four-bladed, fixed-pitch, right-handed propeller characterised by a nominally constant pitch distribution and a very low skew. These characteristics makes the propeller highly loaded at the tip sections and, thus, generate strong tip vortices, which is an important requisite for the subject of the present study.…”

The wake structure of a propeller operating upstream of a hydrofoil

“…In addition, on both upper and lower areas of the hydrofoil a significant deformation of the tip vortices occurs at the leading edge, where the two branches on the two opposite sides of the rudder keep connected. All these results are consistent with earlier experimental and numerical studies in the literature for similar configurations (see, for instance, Muscari et al 2017;Hu et al 2019;Wang et al 2019), where the spanwise displacement of the tip vortices was mainly explained via the image vortex model. Moving across the chord of the hydrofoil the tip vortices tend to lose their coherence, compared to the upstream locations.…”

A DES-SST Based Assessment of Hydrodynamic Performances of the Wetted and Cavitating PPTC Propeller

“…The main advantage of the viscous flow solution method is the possibility of a complete description of the flow features for a wide spectrum of applications, ranging from simple propeller analyses at both model and full scales [16][17][18] to self-propulsion in waves [19] or during maneuvers [20]. They can be relatively easy to apply for various problems such as ventilation of the propellers [21][22][23], oblique flow [24][25][26], wake analysis [27][28][29] and cavitation [30][31][32][33].…”