Water flow model turbine flow visualization study of the unsteady interaction of secondary flow vortices with the downstream rotor

This article presents detailed flow visualization photographs, root mean square processed photography, and computational fluid dynamics (CFD) results of the interaction of the vane passage vortex and horseshoe vortex with the rotor of an axial flow turbine model. Different modes of vortex breakdown behaviour have been experimentally observed inside the rotating passage of the turbine blade. These are spiral vortex mode and bubble mode breakdown. The breakdown mode changes as the vortices are influenced by the periodic pressure field of the rotor. The measurements were taken in a vertical water channel with ink injection for flow visualization. Unsteady CFD analyses have been made with some success in prediction of the unsteady flow structures. In particular, the pre-instability behaviour of the passage vortex in the experiments matches the results of the numerical investigations.