NEAR-FIELD OF A COAXIAL JET WITH AND WITHOUT AXIAL EXCITATION

An experimental study was undertaken to determine the effect of an annular jet on the near-field vortex structure and dynamics of an incompressible axisymmetric jet issuing into a quiescent ambient fluid. The effect of varying the velocity ratio between the two streams was investigated for a single nozzle exit area ratio, a single core flow Reynolds number, and uniform density. A thin laser sheet was used to illuminate the flow for instantaneous photographs of natural and axially excited flow. Natural jet evolution results indicated the initial vortex development in the shear layers occurred independently, but the large-scale structures in the outer layer ultimately controlled the core flow. Axial excitation of the annular flow demonstrated a strong coupling between the large-scale structures in the outer layer and the evolution of the inner layer. Core flow axial excitation produced periodic structures in the inner layer but did not have a significant effect on the evolution of the outer layer.