A.V.Voskoboinick, V.A.Voskoboinick
Vortex motion kinematics on a streamlined surface with a half-cylindrical slot

Acoustic bulletin, Vol. 10 3, (2007) p.30-41
The paper deals with the results of experiments on studying the effect of a local half-cylindrical slot in a hydraulically smooth flat plate on the sources of pseudo-sound fluctuations, structure of the turbulent boundary layer, its kinematical and spectral characteristics. The data of visual investigation of the vortical motion features inside the slot and above the streamlined flat surface are presented. The records by the hot-wire thermoanemometers have shown that coherent vortical systems of various scales occur inside the slot and they are periodically blown out to the boundary layer. As a result of interaction of a turbulent boundary layer, circulatory motion inside the slot and blowout of the vortical systems from it, the local regions of velocity increase and decrease occur, that characterize the processes of acceleration or deceleration the incoming stream near the cavity. In spectral dependencies of velocity fluctuations measured inside the half-cylindrical slot and near it the discrete peaks are revealed. They correspond to the rotation frequency of the large-scale vortex inside the slot, frequency of its blowout to the boundary layer, and first Rossiter shear mode of self-oscillations inside the cavity. Moving off from the slot results in weakening the interaction between the boundary layer and power-intensive pseudo-sound sources of the flow noise generated by vortical motion inside the cavity, that leads to restoring the turbulent boundary layer.
streamlining, a half-cylindrical slot, thermoanemometer, boundary layer, vortex structures