Experimental investigation of the structure interaction in an excited coaxial jet

On the basis of the conditional sampling measurement technique that incorporates the phase information between the flow signals, the development of the flow structures in the initial region of a coaxial jet with mean velocity ratio Λ-1(inner to outer) of 0.3 under acoustic excitation at a frequency of 1.45 kHz and a forcing level of 107 dB were investigated. It was found that a preferred jet column mode for excitation existed. Vortical structures were found in the mixing layers of the jet. Interactions between these structures near the end of the outer potential core of the coaxial jet resulted in the formation of azimuthal structures. Also, the dominant structures beyond the end of the inner potential core were found to be generated from the interactions between the noncoalesced vortices in the outer mixing layer. Their dominance persisted for several diameters downstream of the end of the inner potential core. Results also revealed the importance of the relative positions of the vortices in the development of the coaxial jet.