Active Flow Control of Vortex Rope in a Conical Diffuser

Paper in proceeding, 2015

The vortex rope in a flow similar to 70% of Francis turbine part-load is controlled using the active jet flows injected from the runner crown. The study is undertaken with numerical modeling using hybrid RANS-LES method. The comprehensive study of Javadi and Nilsson (J. Flow, Turbulence and combustion, 2015) is considered as the base case and the effectiveness of the flow control technique used in this paper is compared with the validated numerical results presented in that study. The continuous jets with different momentum fluxes are used. The investigation shows that the pressure pulsation, turbulent structures and the size of the vortex rope decrease with the injected jet from the runner crown. Although the volume flux of the jet is about 4% of whole flow rate of the swirl generator, the momentum flux and the jet position are decisive factors in the effectiveness of the technique.