Estimating the energy contribution of coherent structure in a cylindrical near-wake flow using proper orthogonal decomposition

Abstract

This study identifies the coherent structure and determines its energy contribution in the upstream near-wake behind a long circular cylinder using proper orthogonal decomposition of data that is measured using particle image velocimetry. Members of the harmonic-frequency family (if they exist), which are large-scale, quasiperiodic motions, are firstly identified in the Fourier power spectrum of each mode coefficient. The other large-scaled, organized frequencies of the coherent structure in each mode coefficient are next identified by means of a condition of their peak magnitudes greater than the smallest magnitude of the identified harmonic-frequency family. The kinetic energy that is contributed by the coherent structure is then calculated. Calculation of the kinetic energy of the coherent structure in the first 39 modes, which contribute 80.04% of the total kinetic energy for all eigenmodes, is performed. An estimated 29% of the total kinetic energy is contributed by the coherent structure.

Keywords

• particle image velocimetry (piv)
• proper orthogonal decomposition (pod)
• near wake
• coherent structure
• kármán vortex