Study on Vortex Structures and Intermittency in Two-Oscillating Grid Turbulence With Viscoelastic Fluids Based on Wavelet Analysis

In this paper, two-oscillating grid turbulence with/without viscoelastic additives was performed experimentally by particle image velocimetry. Two classical drag-reducing additives-polymer (Polyacrylamide, PAM) and cationic surfactant (cetyltrimethyl ammonium chloride, CTAC) were chosen. The experiments were carried out under the classical concentration (25ppm) and three different grid oscillation frequencies. Two-dimensional wavelet transform was utilized to investigate multi-scale characteristics of vortex structures and intermittency based on wavelet coefficient. The results showed that at the same decomposition level, the existence of viscoelastic additives attenuates the high-frequency components of fluctuation velocity. The small-scale intermittency is remarkably inhibited by viscoelastic additives especially for scale parameter smaller than 2⁴. Besides, CTAC additives show different effect from PAM additives. Therefore, turbulent drag reduction with additives also happens in two-oscillating grid turbulence without wall effect.