Generation of flow periodicity in a wind-tunnel experiment

The paper presents an experimental analysis of the unsteady velocity field generated by the Periodic Flow Generator (PFG) installed at the wind-tunnel. The measurements were performed for two different designs of PFG which consisted of a row of either cylindrical bars or symmetric profiles. It was found that the wakes generated by the PFG with cylindrical bars were substantially distorted by Karman vortices. The reason responsible for this distortion was the fact that the Karman vortices appeared to be somewhat synchronized with the cylinder-wakes. The PFG built of symmetric profiles proved in turn to be an effective tool for generating the flow unsteadiness which, to some extend, could simulate the flow periodicity encountered at the inlet to the real axial-flow turbine stage.
It was also proved that this periodicity hardly changed the mean flow pattern behind the cascade of turbine blade, but, on the other hand, significantly modified the distributions of both the random and periodic flow disturbances.