The preferred-mode coherent structure in the near field of an axisymmetric jet with and without excitation

Visualization and phase-locked hot-wire measurements have been used to investigate the preferred-mode coherent structure in the near field of an axisymmetric jet for different Reynolds numbers and for the two limiting asymptotic states of the exit boundary layer: laminar and fully developed turbulent. Distributions of phase-averaged longitudinal and lateral velocities, coherent vorticity, coherent and incoherent turbulence Reynolds stresses, and coherent strain rate and production have been obtained over the spatial extent of the coherent structure for a Strouhal number of 0.3. It is found that these properties are independent of the initial conditions, but weakly dependent on the Reynolds number up to about 100,000. The naturally occurring coherent structure in the unexcited jet, educed via an optimized conditional sampling scheme, shows no clear dependence on the jet Reynolds number up to 800,000.