When the vortex line is not positioned at the centric Iine of water tunnel, it is found through numerical calculation that this vortex line will move along a trace of approximate spiral in the cross section plane.

• 当涡线不位于水筒中心线上时,数值计算表明,涡线在水筒截面平面上将沿近似螺旋线的轨迹运动。