摇摆条件下自然循环流动不稳定性非线性演化特性研究

摘要

针对摇摆运动下自然循环流动不稳定性的非线性演化特性进行了分析.应用非线性时间序列分析方法对不同流动状态的时间序列进行幅度谱分析、吸引子重构,并基于相空间重构理论,计算包括关联维数(CD)、Kolmogorov熵(K熵)和最大李雅普诺夫指数(MLE)在内的几何不变量的值,根据计算结果分析了摇摆运动下两相自然循环系统流动不稳定性的非线性演化特性.分析结果表明:随着无量纲功率的增大,系统几何不变量的值先增加后减小,系统由极限环运动经倍周期分岔发展成混沌振荡,最终回到稳定流动；系统非线性特征先增强后减弱,是由于热驱动力、流动阻力和摇摆引起的驱迫外力之间的相互反馈及耦合程度不同所致.%Nonlinear evolution characteristics of natural circulation flow instabilities under rolling motion conditions were studied. Experimental time series of different flow states were analyzed with frequency spectrum and reconstructed phase space. The geometric invariants, including correlation dimension (CD), Kolmogorov entropy (K entropy) and maximal Lyapunov exponent (MLE), were determined based on phase space reconstruction theory. Evolution characteristics of natural circulation flow instabilities under rolling motion conditions were studied based on the results of geometric.