Pavel Jonáš

Dynamics of turbulent spots in transitional boundary layer

The turbulent spots appearance, topology and dynamics on a flat-plate boundary layer in zero pressure gradient during its transition to turbulence is investigated experimentally using time-resolved PIV technique. The intermittently appearing turbulent spots are subjected to detailed study. The hairpin packets organized in regular streamwise rows having fractal structure in the same time are identified in spots. Elongated vortical structures have been recognized in the spots rear-part. The calmed region is characterized by presence of low-velocity streaks originating between the elongated structures.

Some properties of boundary layer under the joint effect of external flow turbulence and surface roughness

Experimental investigation of the boundary layer development on the rough plate (80-grits sandpaper) under external turbulent flows with a grid turbulence of various turbulence scales proved existence of the laminar/transitional region, regardless the surface roughness. Both the outset and the length of the transitional region are affected by the external flow turbulence.

Dynamical structure of the turbulent boundary layer on rough surface

The experiments on structure of turbulent boundary layer on the plane rough wall without pressure gradient are presented. Sand roughness of the wall is considered. Measurements are carried out using Time-Resolved PIV technique in planes parallel and perpendicular to the wall. The results on rough wall are compared with the base case of boundary layer on smooth wall. Hairpin vortices have been detected. Topology and typical size of those structures substantially differ in the cases in question. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Jet in Cross-Flow: A Few Remarks on the Cross-Flow Structure Influence

The results of an experimental investigation of the jet in cross-flow mixing zone are presented. The jet emanates perpendicularly from a circular nozzle in a wall with parallel cross-flow, and a jet to cross-flow velocity ratio of 4 is chosen. The cross-flow was of either low turbulence or high turbulence in nature. The influence of the turbulence level on structures arising in the mixing zone has been studied in detail.