ИСТИНА

In the linear stability theory of shear flows, only a few classical results have been carefully tested experimentally (Blasius boundary layer, Poiseuille flow in a round pipe, the plane Poiseuille flow). Stability of free shear flows, e.g. jets and wakes, and perturbation growth in such flows are much less studied experimentally, because of low critical Reynolds numbers (4.02 for the Bickley jet and 37.6 for axisymmetric jet of ”far-downstream” profile) and free jets breakdown near the orifice. Recently, we invented a novel method for the formation of laminar jets producing the jet of D = 0.12 m in diameter, which stays laminar at the distance 5.5D from the orifice for the Reynolds number ∼ 10 000. Such characteristics provide a convenient way to investigate experimentally the perturbation growth in a free jet. In this study we start such an investigation. By comparing experimental results with theoretical stability analysis, we conclude that the perturbation growth follows the prediction of the linear stability theory up to the transition region of the jet.