Chaotic Phenomena and Analysis of Natural Circulation Flow Instability under Rolling Motion Condition

Experimental study on natural circulation flow instability under rolling motion is carried out and the results show that the complex flow oscillations are formed due to the overlapped effect of the rolling motion (trough instability) and density wave oscillation. The system becomes more instable because of the occurrence of complex flow oscillations. Complex flow oscillations only occur in the case of high subcooling and may be divided into two types: regular and irregular complex flow oscillations. Under the same then-no hydraulic conditions, the marginal stability boundary (MSB) of regular complex oscillations is similar to that of density wave oscillation without rolling motion. And the influences of rolling amplitude and rolling period on its MSB are slight. Chaotic characteristics are found in irregular complex oscillation flow under rolling motion condition. Based on the experimental data and G-P method, correlation dimension and Kolmogorov entropy are gotten with time series analysis. The results show that complex oscillation has fractal dimension and positive Kolmogorov entropy and is typical chaotic time series.