Model-scale Parametric Investigation of the Effects of Propeller Boss Cap Fins on the Hub Vortex and Open Water Efficiency in addition to a Controllable Pitch Propeller Study and a Full-scale Comparison.
Authors
Dam, Patricia ; Jørgensen, Mikkel
Term
4. term
Education
Publication year
2023
Submitted on
2023-06-02
Pages
92
Abstract
Cutting CO2 emissions from shipping is important because the sector contributes about 3%. One option is energy-saving devices such as propeller boss cap fins (PBCF)—small fins on the propeller hub that weaken the hub vortex and reduce energy losses. This thesis uses numerical flow simulations (RANS) to study PBCF performance in open-water conditions and with a downstream rudder. The Q-criterion, a method for identifying vortices in the flow, is used to visualize the PBCF’s effect on the hub vortex. A validated, grid-independent setup supports a parametric study varying four PBCF parameters: chord length, height, pitch, and rake. The best design increased open-water propulsive efficiency by 0.76 percentage points, achieved with a chord length equal to 9% of the propeller diameter. Using this best PBCF, the interaction with a controllable pitch propeller was examined and showed efficiency gains when the pitch-to-diameter ratio exceeded 0.9. Scaling from model- to full-scale simulations with the same PBCF indicated an additional 1.71 percentage-point gain at full scale.
At reducere CO2-udledninger fra skibsfarten er vigtigt, da sektoren står for cirka 3 %. En mulig løsning er energibesparende udstyr som propellerboss-kappefinner (PBCF) – små finner på propellerens nav, der svækker navhvirvlen og mindsker energitab. Denne afhandling undersøger PBCF med numeriske strømningsberegninger (RANS-simuleringer) både i frit vand og med ror nedstrøms. Q-kriteriet, en metode til at identificere hvirvler i strømningen, bruges til at visualisere PBCF’ens effekt på navhvirvlen. En valideret, gitteruafhængig opsætning danner grundlag for et parametrisk studie, hvor fire PBCF-parametre varieres: kordelængde, højde, stigning (pitch) og rake (hældning). Den bedste udformning gav en forbedring af fremdrivningsvirkningsgraden i frit vand på 0,76 procentpoint, opnået med en kordelængde svarende til 9 % af propellerdiameteren. Med denne bedste PBCF blev samspillet med en justerbar stigningspropel (controllable pitch propeller) undersøgt; der blev fundet effektivitetsgevinst for stigning-til-diameter-forhold over 0,9. En skalering fra model- til fuldskalasimuleringer med samme PBCF indikerede yderligere 1,71 procentpoint i gevinst i fuld skala.
[This apstract has been rewritten with the help of AI based on the project's original abstract]
Keywords
PBCF ; CFD ; RANS ; Propeller ; Vorticity ; Maritim ; Model-skala ; Full-skala ; Parameterstudie ; CPP