Investigation of Effective Wake Scaling for Unconventional Propellers
Examensarbete för masterexamen
Naval architecture and ocean engineering (MPNAV), MSc
PERAVALI, SURYA KIRAN
At SSPA model tests are evaluated and scaled to full scale using the ITTC 78 performace prediction method. The ITTC 78 method has been validated against the sea trials over more than 35 years and is very adapted to the conventional propellers. However, new type of propellers such as Kappel propeller seem to challenge the traditional method, in particular with wake scaling. Suspicions have been raised that the standard methods for evaluation of the model tests might give misleading results for Kappel propeller . This report presents a comparative study in various aspects of the performance of a conventional propeller with an unconventional propeller (Kappel propeller). The study is carried out using OpenFOAM RANS solver for computing the viscous flow around a ship hull, propellers in open-water and propellers behind the hull. The numerical results are validated by comparing with the model scale experiments performed at SSPA. Further the computations are extended to full scale and the sources of scaling effects are identified. The differences in scaling between the conventional and unconventional propellers are examined and further this relative differences are compared with that of ITTC 78 scaling method. The correlation of CFD results with the experimental study justify the accuracy of the CFD setup in predicting the complex flow between hull and propeller. In full scale the CFD results show a larger Reynolds scaling effect on the unconventional propeller compared with the conventional propeller in open-water condition. The scaling effects on various full scale performance factors such as the effective wake fraction, thrust deduction, hull and total efficiencies are evaluated for the propellers behind the hull using CFD and compared with the full scale estimations from ITTC 78 method. At the design condition the CFD study estimates the unconventional propeller has much lower effective wake and hull efficiency. However the propeller and total efficiencies are higher for unconventional propeller. The CFD estimations in full scale contradict the estimations from the ITTC 78 method. In this current report the differences between CFD (RANS) and ITTC 78 method are presented and the areas of further research are identified in order to uncover the other discrepancies.
Energi , Produktion , Konstruktionsteknik , Energy , Production , Construction engineering