排水型船於變負荷條件下推進試驗與模擬比較

Abstract

本研究以船模試驗及計算流體力學方法CFD探討排水型船在變動負荷中推進因子及推進效率變化。國際船模拖曳水槽會議ITTC建議船舶推進性能除了在自推點推估實船效率，還能透過變負荷試驗獲得環境負荷變動對於推進效率的影響。 船模試驗以一油輪船模作為研究目標，分別進行阻力試驗、螺槳單獨性能試驗及推進試驗，其中推進試驗採用英式法之試驗流程，並透過給定螺槳轉速，由零推力點至零拖力點為試驗範圍進行變負荷試驗，以計算各組船速下推進係數與轉速的關係，用以進一步求得變負荷相依係數。 CFD則以相同船模之CAD檔進行模擬，透過計算流體力學軟體Star-CCM+求解暫態自由液面Reynolds-averaged Navier-Stokes方程。螺槳採用致動盤模型進行模擬，以節省計算時間。選用船模試驗中之一組船速模擬變負荷試驗，以自推點為參考，在更高和更低的螺槳轉速下，探討推進因子及推進效率與螺槳轉速間之關係，從而計算阻力-推進效率相依係數 ζ_P 與馬力-轉速相依係數 ζ_N ，並與試驗進行比較和探討。 我們可以發現，船模試驗與CFD模擬之各推進係數變化趨勢一致。當船體阻力上升時，螺槳之轉速、推力及推力係數隨之提升，前進係數、推減係數和跡流係數則有下降的趨勢。在推進效率方面，船殻效率、螺槳單獨效率及準推進效率隨阻力增加而下降，試驗中的螺槳對轉效率亦有下降的趨勢。

This study investigates the variation of propulsion factors of a displacement ship under various ship loading conditions by using model tests and Computational Fluid Dynamics (CFD) methods. The International Towing Tank Conference (ITTC) suggests that ship propulsion performance can be evaluated not only by estimating ship efficiency in full-scale at the self-propulsion point, but also by carrying out load variation tests to understand the effect of load variation on propulsion efficiency. The model test selected a tanker model as the research subject, and resistance tests, open-water tests, and propulsion tests are conducted. The propulsion tests followed the British method, with the load variation test conducted by adjusting the propeller rotation rate to determine the relationship between propulsion factors and the rotation rate under different ship speeds. This allowed the calculation of load variation coefficients. CFD simulations were performed with the same model as the model tests, using the software Star-CCM+ to solve the transient free-surface Reynolds-averaged Navier-Stokes equations. The propeller was simulated using the actuator disk model to save computation time. One of the ship speeds from the model tests was chosen for simulation, with load variation tests conducted at higher and lower rotation rates than the self-propulsion condition. The load variation coefficient then be calculated and compared with the results of the model tests for further analysis and discussion. Both the model tests and simulation results show that when hull resistance increases, propeller speed must increase accordingly to maintain ship speed. As the resistance rises, hull efficiency and open water efficiency decrease, the relative rotative efficiency also decreases in the model tests, leading to a reduction in quasi-propulsion efficiency.