TRANSIENT-BEHAVIOR OF AN AXISYMMETRICAL TURBULENT JET

The prediction of the response of unsteady flows submitted to external excitation is a real challenge for the optimization of industrial pro cesses. As the jet flow is a very basic turbulent flow related to mixi ng and entrainment phenomena via turbulent structure dynamic, we inves tigate the transient behavior of an axisymmetric jet submitted to a la rge and sudden decrease of its ejection velocity. The non stationary f low evolution is studied experimentally. Measurements along the jet ax is based on pure ensemble averaging show clearly the convective motion of the perturbation and the adaptation of the local interaction to th e local jet time scale. A transverse investigation in the non stationa ry region show that the mean flow and its turbulence is deeply affecte d during the local velocity decrease.