Wavelet analysis of coherent structures and intermittency in forced homogeneous isotropic turbulence with polymer additives

Large eddy simulation was performed for forced homogeneous isotropic turbulence with/without polymer additives. Wavelet transform in one dimension and two dimensions were performed to investigate the multi-resolution features of coherent structures and intermittency in forced homogeneous isotropic turbulence based on large eddy simulation database. Using wavelet decomposition in one dimension and two dimension, it is found that polymer additives behave inhibitive effect on the intermittent pulse and the amount of coherent structures in forced homogeneous isotropic turbulence. The reconstructions of velocity waveform for coherent structures with strongest intermittence were surveyed at the scale a=2⁶ obtained by maximum energy criterion, showing that the quasi-periodicity and intermittence for coherent structures in polymer solutions are not as distinct as that in the Newtonian fluid. To detect intermittency, the flatness factor and local intermittency measure for velocity fluctuation signals were calculated by wavelet coefficients. The results for flatness factor in one-dimensional wavelet transform and LIM in both one-dimensional and two-dimensional wavelet transform intuitively show that the local contribution to intermittency in polymer solutions flow is relatively smaller, leading to the suppression of intermittency in forced homogeneous isotropic turbulence with polymer additives. The robustness of wavelet transform method has been demonstrated in exploring the characteristics of turbulent structures and intermittency, which are of key importance in understanding the mechanism of turbulent drag reduction.