Low-Frequency Unsteadiness in Turbulent Elliptic Wakes

Velocity fluctuations in the near wake of an elliptic disk are analyzed by the wavelet transform with Morlet wavelet. The wavelet transform demonstrates two dominant periodic components in the velocity fluctuations. The periodic components, which correspond to an alternate vortex shedding in the minor plane and a meandering motion in the major plane, are found to have a low-frequency unsteadiness. The modulus of the wavelet transform reveals that the low-frequency unsteadiness has a central frequency of approximately one-fifth of the frequency of the corresponding periodic component in each plane. Moreover, the unsteadiness is in phase on both sides of the wake in the same plane but out of phase in the different planes. The unsteadiness is of large spatial extent in that the representative wavelength of the low-frequency unsteadiness is of the order of 30 minor diameters.