A Multifractal Cascade Model for Energy Evolution and Dissipation in Ocean Turbulence

Abstract

Scale properties and energy dissipation in the turbulent energy transfer process play an important role in deeply understanding the features of ocean turbulence. In this paper, a universal multifractal cascade model is applied to investigate scale and intermittency properties of a turbulent flow, and two sets of measured turbulence datasets in horizontal and vertical directions are performed for comprehensive experimental verification. First, an empirical mode decomposition method is utilized to adaptively decompose microstructure shear time series into several intrinsic mode functions. Then, the multifractal spectrum is calculated to extract multifractal features for different time scales. The ocean microstructure field shows an asymmetric structure with a left truncation and a long right tail in different directions. This proves that most energy transfer processes occur on small scales. Finally, the calculated multifractal indexes of all intrinsic mode functions for two datasets show that the intermittency of turbulence decreases with the increase in time scales, which reflects the multifractal intensity and the level of intermittency of turbulence. The multifractal cascade model can successfully build a bridge between intermittency and dissipation in the multiscale energy cascade process.