To understand the vortex-ring state and to develop an approach for predicting its boundary, a series of model rotor tests of vertical descent and oblique descent have been conducted on a newly-built test apparatus - t...To understand the vortex-ring state and to develop an approach for predicting its boundary, a series of model rotor tests of vertical descent and oblique descent have been conducted on a newly-built test apparatus - the Whirling Beam. The test results showed some unsteady aerodynamic behavior of the model rotor operating in the vortex-ring state. A very irregular variation of the rotortorque at low rate-of-descent was observed here for the first time. We considered it to be the start of the 'power settling' and determined the critical descent velocity according to this observation. A previous criterion for the vortex-ring state was modified to give a semi-empirical method for predicting the entire vortex-ring state boundary. The computed boundary shows a good correlation with the model test results and the flight experiences.展开更多
为探究水下气体涡环生成及演化的物理机制,运用流体体积(Volume of Fluid,VOF)法两相流模型对涡环生成条件和发展过程进行了模拟,并开展了水下气体涡环发生实验,对比验证了数值模拟结果的准确性。研究表明,水下气体涡环生成及发展需要...为探究水下气体涡环生成及演化的物理机制,运用流体体积(Volume of Fluid,VOF)法两相流模型对涡环生成条件和发展过程进行了模拟,并开展了水下气体涡环发生实验,对比验证了数值模拟结果的准确性。研究表明,水下气体涡环生成及发展需要经历夹断、射流、拉伸和变形4个阶段。通过实验及数值结果数据拟合得到形成有效涡环需要满足的通气压强、通气时间等参数范围,揭示了涡环的结构特征和动力学特性满足Fr相似性准则以及涡量、环量随时间变化的趋势,可为探究水下气体涡环生成及演化规律提供理论借鉴。展开更多
文摘To understand the vortex-ring state and to develop an approach for predicting its boundary, a series of model rotor tests of vertical descent and oblique descent have been conducted on a newly-built test apparatus - the Whirling Beam. The test results showed some unsteady aerodynamic behavior of the model rotor operating in the vortex-ring state. A very irregular variation of the rotortorque at low rate-of-descent was observed here for the first time. We considered it to be the start of the 'power settling' and determined the critical descent velocity according to this observation. A previous criterion for the vortex-ring state was modified to give a semi-empirical method for predicting the entire vortex-ring state boundary. The computed boundary shows a good correlation with the model test results and the flight experiences.
文摘为探究水下气体涡环生成及演化的物理机制,运用流体体积(Volume of Fluid,VOF)法两相流模型对涡环生成条件和发展过程进行了模拟,并开展了水下气体涡环发生实验,对比验证了数值模拟结果的准确性。研究表明,水下气体涡环生成及发展需要经历夹断、射流、拉伸和变形4个阶段。通过实验及数值结果数据拟合得到形成有效涡环需要满足的通气压强、通气时间等参数范围,揭示了涡环的结构特征和动力学特性满足Fr相似性准则以及涡量、环量随时间变化的趋势,可为探究水下气体涡环生成及演化规律提供理论借鉴。
