Harmonic perturbations in turbulent wakes

A theoretical model of harmonic perturbations in far turbulent wakes is considered. The proposed model is based on the triple decomposition method. It is assumed that the instantaneous velocities and pressures consist of three distinctive components: the mean (time-averaged), the coherent (phase-averaged), and the random (turbulent) motion. The interaction between incoherent turbulent fluctuations and large-scale coherent disturbances is incorporated by means of a Newtonian eddy viscosity model. For high-amplitude perturbations, the nonlinear feedback to the mean flow is taken into account by means of the coherent Reynolds stresses. The equations for the mean flow are coupled with the linearized equations for the disturbances, taking into account the mean flow nonparallel effects. The model resolves uncertainties noted in previous theories and provides a correct comparison with available experimental data. The effect of the harmonic perturbations on the turbulent wake growth at high amplitudes is investigated as well.