EXPERIMENTAL INVESTIGATION OF COHERENT STRUCTURE DYNAMICS IN A SUBMERGED FORCED JET

The present work investigates the dynamics of coherent structures, including their scales and intensity, in an initial region of a submerged round forced jet by a Particle Image Velocimetry (PIV) technique for measurements of instantaneous velocity fields and statistical analysis tool Dynamic Mode Decomposition (DMD). The PIV measurements were carried out with 1,1 kHz acquisition rate. Application of DMD to the measured set of the velocity fields provided information about dominant frequencies, contained in DMD spectrum, of velocity fluctuations in different flow regions and about scales of the corresponding spatial coherent structures, contained in DMD modes. Additional calculations of time-spectra from turbulent fluctuations showed good agreement between frequencies of the main harmonics and characteristic frequencies of the dominant dynamic modes. Superposition of relevant DMD modes approximately described nonlinear interaction of coherent structures: vortex formation, their quasi-periodic pairing with modulation amplitude of generated harmonics.

Keywords:
turbulent round jet, periodic forcing, coherent structures, dynamics of vortices, Particle Image Velocimetry, Dynamic Mode Decomposition. 
УДК 532.517.4; 532.525.2; 532.522.2; 533.69.048

EXPERIMENTAL INVESTIGATION OF COHERENT STRUCTURE DYNAMICS IN A SUBMERGED FORCED JET