Propagating helical waves as a building block of round turbulent jets
R. I. Mullyadzhanov (Novosibirsk State University, Institute of Thermophysics SB RAS)
R. D. Sandberg (University of Melbourne)
Sergey S. Abdurakipov (Institute of Thermophysics SB RAS, Novosibirsk State University)
W. K. George (Imperial College London)
K. Hanjalic (Novosibirsk State University, TU Delft - ChemE/Transport Phenomena)
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Abstract
Turbulent jets are known to support large-scale vortical wave packets traveling downstream. We show that a propagating helical wave represents a common form of the "optimal" eigenfunction tracking these structures from the near to the far field of a round jet issuing from a pipe. Two first mirror-symmetric modes containing around 5% of the total turbulent kinetic energy capture all significant large-scale events and accurately replicate the full shear-layer dynamics of the azimuthal wave number m=1. A family of the most energy-containing traveling waves represents low wave numbers and is described in terms of "empirical" dispersion laws.