EXPERIMENTAL INVESTIGATION OF THE STRUCTURE INTERACTION IN AN EXCITEDCOAXIAL JET

On the basis of the conditional sampling measurement technique that in corporates the phase information between the flow signals, the develop ment of the flow structures in the initial region of a coaxial jet wit h mean velocity ratio lambda-1 (inner to outer) of 0.3 under acoustic excitation at a frequency of 1.45 kHz and a forcing level of 107 dB we re investigated. It was found that a preferred jet column mode for exc itation existed. Vortical structures were found in the mixing layers o f the jet. Interactions between these structures near the end of the o uter potential core of the coaxial jet resulted in the formation of az imuthal structures. Also, the dominant structures beyond the end of th e inner potential core were found to be generated from the interaction s between the noncoalesced vortices in the outer mixing layer. Their d ominance persisted for several diameters downstream of the end of the inner potential core. Results also revealed the importance of the rela tive positions of the vortices in the development of the coaxial jet