Three-component vectorial POD of an axisymmetric wake behind a disk

One-component scalar, two-component vectorial and three-component vectorial proper orthogonal decompositions (POD) of the axisymmetric turbulent wake have been studied to investigate possible effects of the number of components constituting the two-point correlation tensor as the kernel of the POD integral equation. A wind tunnel experiment has been performed at 50 diameters downstream of the wake generator, which is a disk of diameter 20 mm. The Reynolds number based on disk diameter is 20 000. 12 cross hot-wires were used to obtain the simultaneous multi-point measurements. 6 of the probes were located on a fixed rake and the other 6 probes were located on a movable rake which was traversed from 10° to 180° in 10° increments. Two experiments were carried out to obtain first the streamwise and azimuthal components of the velocity , and then to obtain the streamwise and radial components of the velocity. The remaining two two-point spectra were extracted from the data using the continuity equations. The one-component scalar, and two- and three-component vectorial decomposition results are essentially the same. For these cases eigenvalues integrated over frequency showed that Fourier mode-2 has a clear dominance. Azimuthal mode-2 has a peak at the near-zero frequency, while azimuthal mode-1 has a peak at a frequency which corresponds the vortex shedding frequency.