Investigation of the effects of a fan-shaped Mewis duct before a propeller on propulsion performance

Abstract

To define the guidelines for the design of a Mewis duct for a small bulk cargo ship, a numerical study was carried out to investigate the effects of a fan-shaped Mewis duct on propeller performance of a 38,000 t bulk cargo ship with a three-blade propeller. Calculations were performed using the STAR-CCM+ software based on the solution of the Reynolds averaged Navier-Stokes (RANS) equation. Computations were carried out for a wide range of locations from 0.11D to 0.21D upstream from the propeller disc, a radius of trailing edge from 0.65R to 1.05R, and angle of attack of the inner fins, where from 0° to 10° of the fan-shaped Mewis duct, where D is the diameter of the propeller and R is the radius of the propeller. With the installation of the duct, the axial mean wake fraction on the propeller disc decreased, while the tangential mean wake fraction increased significantly. As the installation position was far away from the propeller, the axial mean wake fraction varied in a wave pattern, while the tangential mean wake fraction increased. With the increase of the radius and the angle of attack of the inner fins of the duct, the axial mean wake fraction first decreased and then increased, while the tangential mean wake fraction increased gradually. Correspondingly, the propeller force coefficients and efficiencies with the duct were all more than those without the duct and changed with the variations of the duct parameters. When the propeller and duct were taken as a propulsion system, the efficiency of the system was less than that of only the propeller. At the same time, with variations of the location, radius, and angle of attack of the inner fins of the duct, the efficiency of the system first increased and then decreased gradually, which indicates that there was an optimum design value for all of the duct parameters. Moreover, only when the design of these duct parameters are reasonable can energy savings be achieved; otherwise, the opposite effect is produced. Eventually, with the installation of the fan-shaped Mewis duct, the wake harmonic degree on the propeller disc can be significantly improved.

Numerical Simulations of the Hydrodynamic Performance of the Propeller with Wake Equalizing Duct behind the Ship

“…𝜀 and k are found by semi-experimental Eqs. ( 10) and (11). In the following relation, 𝜎 𝜀 is the turbulent Schmidt number and equal to 1.3, 𝜎 𝑘 is the Prandtl number and equal to 1, G (shear production term) is the turbulence kinetic energy produced by the average flow-turbulent flow field interaction and B is the production-buoyancy loss due to the flow fluctuating density field.…”

“…Many numerical and experimental works were carried out to analyze and design the ESD [6][7][8][9][10][11]. Using the vortex lattice method (VLM) and defining a propeller blade surface replaced by the vortex distribution.…”

Analyzing the performance of hull and water jet propeller under mooring conditions: effects of shallow water depths and varying inflow speeds

“…As the interaction between the water jet propeller system and the hull differs significantly from a traditional, separate water jet propeller system, CFD technology can be useful in simulating and predicting the model prior to experimentation. Chang et al (2018) utilized Reynolds average stress method (RANS) solution to explore the effect of energy-saving ducts on propeller performance in hulls with sector-shaped ducts installed in front of the propeller. Their findings revealed that the presence of the energy-saving ducts enhanced the propeller efficiency.…”

Pre-Swirl Ducts, Pre-Swirl Fins and Wake-Equalizing Ducts for the DTC Hull: Design and Scale Effects

“…Often, indeed, improvements observed at the model scale were not completely confirmed in full-scale, suggesting the need to account for Reynolds effects in the very preliminary phase of the process to exploit possible additional savings. Systematic analyses of several ESD concepts [25] have evidenced the strict connection of the hull shape (and relative flowfield) to the ESD geometry and its capability to provide positive effects on the propulsion system. Self-propulsion modeling, in a similar way in this context, appeared as the most appropriate framework for the evaluation (and the exploitation, during the design process) of the ESD-propeller-hull interactions and to account for the most suitable "key performance indicators" driving the design of the device.…”