Coherent structure extraction in turbulent channel flow using boundary adapted wavelets

This article is dedicated to Professor Javier Jimenez on the occasion of his 70th birthday. The computations were carried out on the FX100 systems at the Information Technology Center of Nagoya University. M.F. and K.S. acknowledge support by the French Research Federation for Fusion Studies within the frame- work of the European Fusion Development Agreement (EFDA).International audienceWe present a construction of isotropic boundary adapted wavelets, which are orthogonal and yield a multi-resolution analysis. We analyze direct numerical simulation data of turbulent channel flow computed at a friction Reynolds number of 395, and investigate the role of coherent vorticity. Thresholding of the vorticity wavelet coefficients allows to split the flow into two parts, coherent and incoherent vorticity. The coherent vorticity is reconstructed from their few intense wavelet coefficients. The statistics of the coherent part, i.e., energy and enstrophy spectra, are close to the statistics of the total flow, and moreover, the nonlinear energy budgets are very well preserved. The remaining incoherent part, represented by the large majority of the weak wavelet coefficients, corresponds to a structureless, i.e., noise-like, background flow whose energy is equidistributed