|Insanu Abdilla Cendikia Abar||Institut Teknologi Sepuluh Nopember, Jl. Raya ITS, Keputih, Kec. Sukolilo, Kota Surabaya 60111, Indonesia|
|I Ketut Aria Pria Utama||Institut Teknologi Sepuluh Nopember, Jl. Raya ITS, Keputih, Kec. Sukolilo, Kota Surabaya 60111, Indonesia|
In order to understand the effect of modifying the traditional form of propeller hub into the propeller boss cap fins (PBCF) form, a series of tests was conducted to discover the best type. Analysis was made using the computational fluid dynamic (CFD) approach, together with ANSYS CFX code. Two types of hub were employed, namely convergent and divergent. Both types were made using slope angles of 5, 10 and 15 degrees. Comparative analysis of the data was made, combined with validation by published papers. The overall results indicate that compared to a normal hub, the traditional convergent type has an increased efficiency of around 1.4%, while the divergent type decreases efficiency by approximately 1.2%. Furthermore, the PBCF convergent hub results in increased efficiency of around 0.8%, whereas the divergent type decreases efficiency by about 1.0%. This study is in good agreement with previous papers, with a discrepancy of approximately 2%.
Energy saving devices; Hub vortex; Propeller boss cap fins
Propeller boss cap fins (PBCF) have been used since 1988 as an innovative energy saving device in marine transportation, according to the International Towing Tank Conference (ITTC). The addition of PBCF can improve the efficiency of a ship's propeller. The other function of PBCF is to eliminate the vortex phenomenon on the hub part of the rotor. It has been evidenced by Dang et al. (2011), Kawamura et al. (2012), Cheng and Hao-Eng (2014), Molland et al. (2014), and Sun et al. (2016) in research based on field studies, lab trials and computational fluid dynamic (CFD) simulations that PBCF can eliminate the vortex and improve the efficiency of ships’ propellers. Considering design parameters, PBCF will influence propeller efficiency noticeably (Seo et al., 2016; Mizzi et al., 2017).
In the past few decades, research on PBCF geometry has been conducted to discover which components of PBCF are highly sensitive to efficiency and the hub vortex phenomenon. Several papers (Ghassemi et al., 2012; Druckenbrod et al., 2015; Kimura et al., 2018) have found that variations in PBCF fin position are highly influential on propeller efficiency and added hub configurations indicate can affecting vortex in the hub cap area. This has led to the indication that the shape of the hub geometry has an effect on the shape and magnitude of the vortex, as stated by Katayama et al. (2015). The geometry of the hub propeller is divided into three parts, convergent, straight and divergent, with each type having a different vortex characteristic.
In addition, Katayama et al. (2015) undertook
research on the addition of updated PBCF using convergent hub types, and obtained
good efficiency. However, this does not apply to the research on the type of
divergent hub conducted by Lim et al. (2014),
who found decreased propeller system efficiency. These two issues are the basis
for this research.
CFD simulation focuses on varying the inclined angle of the hub cap (convergent and divergent types) and then converting it into PBCF. Furthermore, each type of hub cap has varying incline angles of 5, 10 and 15 degrees. Comparison is made between each type of conventional and PBCF hub in order to obtain the best results.
CFD has been fairly successfully used to simulate and demonstrate the use of PBCF on propeller hub caps. The results are excellent for the convergent hub, whilst the divergent one shows a disappointing output. The convergent hub increases efficiency by around 1.4% compared to conventional one, which rises further by approximately 0.8% after being converting into PBCF. On the other hand, the divergent hub decreases efficiency by around 1.2%, with a further decrease of approximately 1% after being converting into PBCF.
In addition, the incline angle can influence the increase or decrease in efficiency. The reason for this is attributed to the decrease in the pressure area on the convergent hub and the increase on the divergent one. This occurs because in the case of divergent hubs the pressure drops and the shape of the flow is affected, resulting in the emergence of hub vortices.
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