Time-frequency analysis of pressure fluctuations on a hydrofoil undergoing a transient pitching motion using Hilbert-Huang and Teager-Huang transforms

In this paper, time-frequency analysis of wall pressure signals of a hydrofoil's suction side undergoing a forced transient pitching motion with incoming flow is conducted. A novel method recently introduced by Huang et al., the Empirical Mode Decomposition (EMD), is first used to decompose resulting non-stationary signals into frequency sub-band components called Intrinsic Mode Functions (IMFs). EMD-filtered pressure coefficient signals are then reconstructed from few selected IMFs from low frequency modes and time-frequency analysis performed on high frequency modes. For this latter purpose, two analysis methods are used. The first one consists in demodulating IMFs into their Instantaneous Amplitude (IA) and Instantaneous Frequency (IF) using the Hubert transform and the second one is based on the Teager energy tracking operator (TEO). The transition occurrence is analyzed using IA and IF of extracted IMFs from chordwise pressure transducer's signals. This transition occurrence is then described in time-frequency domain.