Scale effect propeller calculations : twin screw wake field

Abstract

This Master Thesis is all about scale effects which appears in results after performing model and full scale simulations of a twin screw vessel hull, which is anchor handler (STX-413). In this project main purpose is to perform towing tank tests where main considerations are done on results which contain resistance force coefficients and nominal wake fraction on a propeller plane. These are compared to each other in a range of Froude numbers. Simulations for model and full scale ship are done by software called STAR CCM+. Computations has been performed on a case where hull does not have ability to sink and trim. In general all set up for computations was given by Marintek as an example. Because there is no experimental data to validate computational results, in thesis are done several different calculations to compare with: two different turbulence models are tried, calculations made with several different time steps to determine which is best for each case (model and full scale), and few simulations containing different domain size in number of cells. Main results shows that pressure force coefficients are lower in full scale up to 17% and wake fraction distribution follows the same: in full scale averaged values in propeller plane in certain Froude numbers are up to 28% lower than in model scale computations. Conclusions gives an indication that it needs to have further investigation regarding these scale effects on this particular vessel which is under investigation.