随轴系做复杂空间运动的船舶螺旋桨水动性能计算

The calculation of the hydrodynamic performance of propellers undergoing complex motion due to the shaft

船舶航行时,附在转轴上的螺旋桨通常做复杂的空间运动。这是因为一方面螺旋桨和转轴不可避免地存在偏心,使得在不平衡激励下转轴在绕自身中心线旋转的同时又发生空间涡动(又称为进动);另一方面,螺旋桨通常工作在不均匀的流场中(即使来流均匀,轴系涡动亦会导致流场的不均匀),桨叶表面的脉动力也会导致转轴的空间振动。对具有复杂三维运动的螺旋桨的水动性能预报是一个难点。本文建立了螺旋桨在流场中随轴系做复杂空间运动时的水动力预报数学模型,并利用不定常面元法求解了这一问题。该方法按时间步顺序求解,考虑了不均匀流场、轴系振动、尾涡的非线性运动及卷曲等因素。利用本文提出的方法并结合结构动力学模型,可以方便地研究流体-螺旋桨-轴系双向流固耦合等问题。同时该方法也可以用来预报船舶转弯、船舶升沉及纵摇振荡、螺旋桨启停及加速等复杂工况下的螺旋桨水动性能。文中通过一个算例验证了算法的有效性。最后,预报了轴系纵向振动幅值为1 mm,振动频率为3 Hz并伴有微量回旋振动时所引起的4381螺旋桨的脉动力。研究表明推力脉动分量大约为其静态分量的4.5/1 000,扭矩脉动分量大约为其静态分量的4/1 000。

The propeller attached at the shaft usually undergoes very complex motion. This is because the propeller and the shaft have inescapable eccentricity, and then the shaft has two kinds of motions under unbalance excitation i.e. rotation and whirling. On the other hand, the propeller usually operates in a spatially nonuniform wake (even the incoming flow is uniform, the shaft whirl motion also leads to the nonuniformity), then the fluctuant pressure of blades causes the vibration of the shaft. It is very difficult to predict the hydrodynamic performance of the propeller undergoing the complex motion. In this paper, the mathematical model for hydrodynamic performance prediction of the marine propeller, which has a complex motion with the shaft, is established and solved by unsteady potential panel method. The time stepping algorithm, the non-uniform wake field, the vibration of the shaft, the free wake modeling and so on are considered in this method. The method can be used to solve the fluid-structure interaction of fluid-propeller-shaft system. In addition, it also can be applied to predict the hydrodynamic performance of a propeller when it suffers complex circumstances, such as the turning of ships, the vibration of ships, the start-stop and speeding up of propellers. The validity is verified by a numerical example. At last, the pulse force of propeller 4381 is predicted when the axial vibration amplitude of the shaft is 1 mm and the frequency is 3 Hz. The result shows that the pulse thrust is 4.5/1 000 of the static thrust and the pulse torque is 4/1 000 of the static torque.