Experimental and Numerical Study of Pre-Swirl Stators PSS

Abstract

Energy saving within shipping is gaining more attention due to environmental awareness, financial incentives, and, most importantly, new regional and international rules, which limit the acceptable emission from the ships considerably. One of the measures is installation of energy saving devices (ESD). One type of such a device, known as pre-swirl stator (PSS), consists of a number (usually 3 to 5) of fins, which are mounted right in front of the propeller. By modifying the inflow and swirl into the propeller, the fins of a PSS have the possibility to increase the total propulsion efficiency. However, at the same time, they may introduce additional resistance either due to changes in pressure distribution over the aft ship or due to its own resistance of fins. In this paper, the authors present experimental and numerical investigation of a PSS for a chemical tanker. Numerical analysis of the vessel with and without PSS is performed in the model and full scale. Model testing is performed with and without PSS to verify the power savings predicted numerically. Among other quantities, 3D wake field behind the hull is densely measured at different planes, starting from the PSS plane to the rudder stock plane. 3D wake measurements are also conducted with a running propeller. The measurements show considerable improvement in the performance of the vessel fitted with PSS. On the numerical side, analyses show that scale effect plays an important role in the ESD performance. Investigation of the scale effect on the vessel equipped with an ESD provides new insight for the community, which is investing more into the development of energy saving devices, and it offers valuable information for the elaboration of scaling procedures for such vessels.

Pre-swirl fins design for improved propulsive performances: application to fast twin-screw passenger ships

“…The in-plane component of the velocity is negligibly more oriented in the vertical direction when considering the influence of the free surface, and the shaft vortices development is slightly different. Overall, the results resemble the conclusions of Koushan et al (2020) and Gaggero et al (2017), allowing for reasonable predictions of the unsteady propeller performance behind the hull regardless of the inclusion of the free surface effect.…”

“…In the framework of the EU project GRIP (Streckwall and Xing-Kaeding 2017;Schuiling and van Terwisga 2017;Prins et al 2016), pre-swirl stators reached an energy-saving of 6%, that in the particular case of a twin-screw passenger vessel was close to 4%. Koushan et al (2020) developed pre-swirl stators for a chemical tanker and their numerical results, claiming a power savings of 2.5%, were confirmed during a dedicated model-scale experimental campaign. The usage of flapped and "controllable" pre-swirl stators was proposed to cope with non-constant operative conditions (slow steaming, fouling, weather, change of draft) and to ensure the highest possible energy-saving, which reached a shaft power reduction of 4% in the case of a bulk carrier (Nielsen and Jin 2019).…”

“…Since the mutual interactions between the wave pattern and the pre-swirl appendages can be considered negligible, at least in the preliminary design phase, an additional simplification for the self-propulsion estimation concerns the calculation of the current ship resistance (i.e., in presence of the ESD) starting from the double-model assumption, as successfully done in many similar cases (Gaggero et al 2017;Koushan et al 2020). A "constant" wave resistance contribution, i.e., independent of the propeller working condition and ESD, can be computed by subtracting the double model drag to the total hull resistance calculated in towing conditions with the free surface.…”

Study on Compact Pre-Swirl Duct for Slender Aft-Body Crude Oil Carrier

“…Kim et al [7] developed an asymmetric pre-swirl stator better performance, efficiency, and cavitation in consideration of the upward flow stern body of a ship [13][14][15]. Koushan et al [16] published a paper about the exper and numerical study of PSS for chemical tanker, and Su et al [17] studied the influ a PSS and rudder bulb system on the propulsion performance of a large-scale ship Recently, the structural performance of PSS is also being actively studied. Bakica e proposed a numerical analysis method that could predict the hydrodynamic lo structural responses of PSS.…”

Simulation strategy of the full-scale ship resistance and propulsion performance

“…However, the scale effect causes a large error in the process of converting the model test data for the difference in the Reynolds number (Raven et al, 2008). Although there are empirical formulas that can be used to correct this error, serious problems concerning the wake adapted propeller design (Wang et al, 2017(Wang et al, , 2018 and energy-saving effect analysis for the energy-saving device exist (Song et al, 2020;Koushan et al, 2020). With the recent developments in computer software, hardware technology, and numerical simulation methods for fluid mechanics (Salih et al, 2019;Su et al, 2019), the powering performance of full-scale ships, which is based on computation fluid dynamics (CFD), is being actively researched.…”