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考虑气核生长溃灭效应的螺旋桨梢涡空化初生数值模拟研究

NUMERICAL SIMULATION OF PROPELLER TIP VORTEX CAVITATION INCEPTION CONSIDERING THE EFFECT OF NUCLEI GROWTH AND COLLAPSE

  • 摘要: 梢涡空化是螺旋桨最早发生的空化类型, 其一旦发生会显著增强舰船辐射噪声水平. 因此, 螺旋桨梢涡空化初生的预报是军舰临界航速确定的关键, 长期以来受到船舶领域诸多专家学者的重点关注. 微观气核受涡心低压作用而发生暴发式生长是梢涡空化初生的重要机制, 而传统欧拉框架下的宏观空化模型用经验参数模化了微观气核的影响而无法对该过程准确模拟, 影响对螺旋桨空化初生的准确预报. 为了弥补传统模拟方法的不足, 本研究发展并使用一种基于气泡动力学并考虑水相可压缩效应的欧拉−拉格朗日空化初生数值预报方法对螺旋桨梢涡空化初生进行了数值模拟研究. 与实验结果对比表明, 该模型能够准确地预报螺旋桨梢涡空化初生. 此外, 本研究不仅从微观气核角度探究不同来流气核尺寸对空化初生的影响, 还进一步研究梢涡流动特性对气核演变的影响机制, 初步探究初生空化在螺旋桨梢涡流场中的发声机理. 在空化初生光学判断准则下尺寸越大的气核越容易被梢涡捕获而暴发式生长. 气核在梢涡卷吸作用下逐渐靠近涡心低压区. 在涡心低压区的持续作用下气核开始暴发式生长, 并在半径达到最大后迅速收缩溃灭, 产生强烈的正声压脉冲信号.

     

    Abstract: Tip vortex cavitation (TVC) is the earliest type of cavitation that occurs on propellers, and it significantly enhances the underwater radiated noise level of ships once it happens. Therefore, TVC inception prediction is vital for cavitation inception speed determination and has attracted much attention from experts and scholars in the ship field. The explosive growth of microscopic nuclei under the action of low pressure of vortex core is an important mechanism for tip vortex cavitation inception, while the conventional macroscopic cavitation models in Eulerian framework use empirical parameters to model the influence of microscopic nuclei and cannot accurately simulate this process, which affects the accurate prediction of propeller cavitation inception. To overcome the limitations of traditional simulation methods, this paper develops and applies an Eulerian-Lagrange cavitation inception numerical method based on bubble dynamics and water phase compressibility to simulate TVC inception. Comparison with experimental results shows that this model can accurately predict propeller TVC inception. This paper not only investigates the effects of different incoming nuclei sizes on cavitation inception from a microbubble perspective, but also studies the significant influences of tip vortex flow characteristics on nuclei evolution, and thus reveals the sound generation mechanism of cavitation inception in propeller tip vortex flow field. Under optical criterion for cavitation inception, larger-sized gas nuclei are more likely to be captured by tip vortices and grow explosively. Nuclei gradually approach the vortex core low-pressure region under tip vortex suction. Nuclei grow explosively under continuous low-pressure action at the vortex core, and rapidly contract and collapse rapidly after reaching maximum size, producing strong acoustic pressure pulse.

     

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