Analysis of multi-scale fractal characteristics of severe slugging based on Hurst exponent
Based on the multi-scale method and Hurst analysis,the multi-scale structure and nonlinear characteristics of severe slugging flow were studied in the present work.Experimental investigation on severe slugging were performed in pipeline-riser system using air and water and the signal of pressure difference was recorded.Based on db4 wavelet,the signal of pressure difference was decomposed and reconstructed at 1-8 scales.The dynamics characteristics of gas-liquid two-phase flow at each individual scale were extracted.It was found that the transient process of gas blowout and liquid fallback in severe slug flow was mainly reflected in the detail signals at d5—d8 scales.The result of Hurst exponent analysis on the decomposed signals of pressure difference fluctuation shows that severe slug flow has significant bi-fractal characteristics,which are constrained by two dynamic factors,i.e.positive persistence and anti-persistence.However,the approximate component and the detail component exhibit completely opposite fractal structures.The approximate component has positive persistence,while the detail component has anti persistence.The detail component at scale d1 describes the interaction between micro-scale bubbles.The meso-scale interaction between liquid phase and gas bubbles was reflected by the detail components at the d2—d5 scales.The macro-scale interaction between gas-liquid phase and the pipe wall was described by the detail components at the d6—d8 scales.The energy of the pressure difference fluctuation signal is mainly distributed at the macro-scale.
severe sluggingdifferential pressuremulti-scalefractalgas-liquid flowHurst exponent
万方数据
维普
