紧急制动及紧急向前时螺旋桨绕流的大涡模拟

船舶在港口停泊或在过驳、动力定位作业过程中需要进行复杂的操纵,此时船舶需要在低速非设计工况下实现后退、紧急制动和紧急向前等运动。在这些低速操纵运动过程中,螺旋桨工作于四象限内,由此产生的侧向力会影响船舶的操纵性能。出于安全考虑,需要评估螺旋桨在四象限内的水动力性能。文章基于CFD方法模拟了螺旋桨在四象限内作业时的紧急制动和紧急向前工况,采取LES方法模拟了紧急制动和紧急向前时剧烈的非定常分离流动。对紧急制动工况进行了网格收敛性分析;所得到的推力和扭矩系数与现有的试验值进行了比较,分析了螺旋桨负荷对螺旋桨性能的影响。通过对桨叶表面的压力分布、一些典型平面上的速度轮廓和流线以及推力的频谱特性进行分析,展示了螺旋桨流动的机理。

LES Simulations of the Flow Around a Propeller in Crash Back and Crash Ahead

Complex maneuvering occurs when a ship berths inside a port or operates during lighter-ing or dynamic positioning.The ship needs to maneuver in off design conditions at low speed like moving backward, crash back and crash ahead. During these low speed operations, the propeller op-erates in four quadrants. Side force is generated, which may affect the ship maneuverability. It is es-sential to assess the hydrodynamic behavior of a propeller under four quadrant conditions for safety issues. In this paper, CFD simulations are performed for a propeller operating in crash back and crash ahead during operation in four quadrants. LES is applied under crash back and crash ahead condi-tions for the resolution of highly unsteady separated flow. Grid dependency study in crash back is car-ried out. The obtained thrust and torque coefficients are compared with available experimental data. The influence of propeller loading on the propeller performance is analyzed. Flow details like pres-sure distribution on the blades, velocity contour with streamlines on some selected planes and spectral characteristics of the thrust are analyzed to show the mechanism of the propeller flow.