APPLICATION OF A WAVELET CROSS-CORRELATION ANALYSIS TO DNS VELOCITY SIGNALS

A wavelet cross-correlation analysis is applied to the velocity signal s derived from axisymmetric direct numerical simulations of a coaxial jet configuration. It is shown that this technique allows determinatio n of the time intervals and scales contributing to the Reynolds stress es, and thus an assessment of the level of intermittency of this contr ibution at the Various scales. The availability of the vorticity field from the numerical simulations makes possible association of the roll -up, passage and pairing of vortical structures with average, spectral and instantaneous contributions to the Reynolds stresses. High values of Reynolds stresses are found in;he roll-up region, where the axial and radial velocity fluctuations have a small phase lag for significan t times intervals. Conversely, further downstream the passage of appro ximately symmetrical vortices, although giving rise to high velocity f luctuations, does not produce significant Reynolds stresses because th e two velocity signals are nearly orthogonal for most of the time. Thi s demonstrates that eduction schemes based on the energy of the veloci ty fluctuations might not adequately reproduce the flow features chara cterizing the Reynolds stress production.