The Wake Flow Behind Azimuthing Thrusters: Measurements in Open Water, Under a Plate and Under a Barge

Abstract

The wake flow behind a ducted azimuthing thruster was investigated. The thruster wake is an important factor in thruster interaction effects. Model tests were carried out for 3 different configurations; a thruster in open water conditions, a thruster under a flat plate and a thruster built into a barge. Two different thrusters were considered, a ‘normal’ thruster with a horizontal propeller axis and a ‘tilted’ thruster with a propeller axis and nozzle oriented 7 deg down-wards. In the tests the propeller thrust and torque were recorded, as well as the nozzle thrust and unit thrust. The velocities in the wake of the thruster were measured using a PIV (particle image velocimetry) system, for down-stream locations up to x/D = 19. The influence of the thruster tilt, the plate above the thruster and bilge radius on the thruster wake flow were investigated. Detailed PIV measurements were carried out on the wake flow behind the thruster in open water conditions. The PIV system used can measure 3D velocities in large set of points in a 2D plane, which is illuminated by a laser light beam. The flow velocities were measured in a large number of cross sections at different distances from the thruster. The PIV measurements provide a detailed image of the flow velocities in the thruster wake, showing the axial velocities, as well as the rotation and divergence of the wake. Subsequently, PIV measurements were carried out for the thruster under a flat plate and the thruster under a barge. The measurement results show a thruster wake that is deformed by the presence of the plate and the barge. The plate and the bottom of the barge form a flat plane above the thruster, clearly flattening the cross section of the thruster wake. Furthermore, the wake flow at the side of the barge, near the bilge radius, results in a low pressure region, causing the wake flow to diverge up as it flows from under the barge into the open water. This phenomenon is known as the Coanda effect and is strongly dependent on the bilge radius and the distance between the thruster and the side of the barge. The effect of both these parameters was confirmed in the model test results presented. The typical flow patterns observed as a result of the Coanda effect are illustrated in Figure 1 below. The results of the present model test research are used to further improve the understanding of the physics of thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations.

Effects of a nozzle on the propeller wake in an oblique flow using modal analysis

“…The wake dynamics of a four-bladed, fixed-pitch, right-handed propeller (S5810 R) with and without a nozzle (1393 type 19A) operating in axisymmetric and oblique flows are compared in this study. The propeller and nozzle models are chosen because they are designed to eliminate the undesirable hub vortex (Cozijn et al 2010;Cozijn & Hallmann 2012;Maciel et al 2013;Koop et al 2017) and allow us to investigate wake destabilization in the absence of hub vortex interference. Figures 2(a per second).…”

“…The Reynolds number based on the rotational speed is Re n = nD 2 /ν = 1.765 × 10 5 , where D = 0.1 m is the propeller diameter. The model parameters, rotational speed and Reynolds number are chosen to match previous experimental settings (Cozijn et al 2010;Cozijn & Hallmann 2012) and numerical settings (Maciel et al 2013;Koop et al 2017).…”

“…In the present work, numerical research on the wake dynamics of an NP and DP with the same propeller geometry working at five inflow angles (α = 0°, 15°, 30°, 45°and 60°) is conducted to evaluate the effect of the nozzle on the wake deflection and to explore the differences in the evolution characteristics and destabilization mechanisms between NP wakes and DP wakes in an oblique flow. The propeller (S5810 R) and nozzle (1393 type 19A) geometries are chosen, as the DP is designed to eliminate the undesirable hub vortex (Cozijn, Hallmann & Koop 2010;Cozijn & Hallmann 2012;Maciel, Koop & Vaz 2013;Koop et al 2017) and it gives us a chance to evaluate the far-wake meandering in yawed conditions without interference from a hub vortex. A moderate advance coefficient of J = 0.4 is chosen because this operating condition is full of rich destabilization mechanisms (Magionesi et al 2018;Zhang & Jaiman 2019;Shi et al 2022).…”

Effects of Parallel-Middle-Body Relative Length and Stern Form on the Wake Fraction and Ship Resistance

“…A larger value of wake fraction results in a less efficient propeller [2]. Thus, a ship with a larger wake fraction will require a larger power than a similar ship (with the same displacement) with a smaller wake fraction in order to achieve the same ship speed [3].…”

Thrust allocation algorithm considering hydrodynamic interactions and actuator physical limitations.

“…Computational Fluid Dynamics (CFD) (Cozijn and Hallmann 2012) and model based (Arditti and Tannuri 2012) tests show that hydrodynamic interactions can drastically influence the net thrust. The work presented in Arditti et al (2014) and Arditti et al (2015), with some simplifications in the representation of hydrodynamic interaction, illustrates that by considering these phenomena in the thrust allocation higher reliability and minimization of power consumption can be achieved.…”