NONLINEAR-ANALYSIS OF NEAR-WALL TURBULENCE TIME-SERIES

We present the results of the nonlinear analysis of a near-wall turbul ence signal, measured using a Laser Doppler Anemometer. Despite being preliminary in part, the results highlight some interesting aspects of the dynamics of coherent structures. Careful reconstruction of the dy namics from the scalar time series highlight particular phases of the bursting cycle, corresponding to the VITA detections, immersed in the overall high-dimension dynamics: the possibility to distinguish these trajectories in the embedding space provides indications for condition al sampling techniques on the reconstructed attractor. The application of nonlinear prediction to a system of high-dimension produces foreca sts of rapidly decreasing quality over time, with no consequences for practical applications. Much more interesting instead is the analysis of the forecast errors for very short forecast intervals, where we obs erved a greater difficulty to predict the beginning of coherent struct ure instability probably due to the quasi-random forcing of the outer flow.