The object of investigation was the one-strand tundish with flow control device such as gas permeable barrier (GPB). The aim of this flow control device was to activate the motion of liquid steel in the tundish longitudinal axis region. Computer simulation of the liquid steel flow and argon behaviour in isothermal turbulent motion conditions was done using the Ansys-Fluent computer program. For the validation of the hydrodynamic patterns obtained from computer simulations, a isothermal tundish glass model was used. Tundish glass model enables the recording of the visualization of fluid medium motion through the particle image velocimetry (PIV) method. Based on computer simulations, the liquid steel flow path lines in the tundish with GPB was obtained. For explain the hydrodynamic phenomena occurring in the tundish working space, the Buoyancy number has been calculated.