An improved BEMT model based on agent actuating disk with application to ship self-propulsion simulation

Propeller body-force model is a low-cost tool for numerical simulation of the ship self-propulsion test compared with discretized propeller model. As one of the most traditional theories of propeller model, Blade Element Momentum Theory (BEMT) has been proved to have considerable application potential with stability and accuracy. However, it's still hard for BEMT to keep accuracy in a relatively large range of working conditions due to unproved prior assumptions, which limits the application of BEMT in complex inflow conditions like ship self-propulsion. In the application of BEMT, the calculation method of Angle of Attack (AOA) has a great influence on the accuracy. In this paper, an "Agent Actuating Disk (AAD)" method is proposed to determine the AOA. AAD-BEMT method uses AAD to obtain the relationship between local velocity and inflow velocity so that the AOA can be defined by geometric Angle of Attack. This consideration avoids the inaccuracy of determining AOA by local velocity from discretized propeller flow field. The KP505 propeller open-water test is chosen to verify the accuracy of the proposed AAD-BEMT method. Then the numerical simulation of a KRISO Container Ship (KCS) self-propulsion test (Fr = 0.26) is carried out to investigate the performance of the AAD-BEMT body-force model as well as other different propeller models when dealing with non-uniform ship's wake. The open-water curve, propeller load distribution, and self-propulsion factor are presented and compared with the available experimental data. The results show that the predicted load distribution is accurate. In addition, not only the thrust and torque of the AAD-BEMT model can have a stable accuracy in a wide operating condition, but also the wake agrees well with the experimental result, which means that the proposed AAD-BEMT model can economically and accurately simulate the momentum transport of propeller under complex hull-propeller interaction condition.