On the relevance of the runner crown for flow instabilities in a Francis turbine

Abstract The precessing vortex core (PVC), also known as rope, in a draft tube of Francis-99 hydro turbine is investigated. goal to increase our comprehension the root PVC order attenuate or suppress PVC, thus extending stable operational range below best efficiency point at part load conditions. Unsteady Reynolds-averaged Navier– Stokes simulations are conducted and used basis for all analyses performed this work. discrete Fourier transform (DFT) spectral proper orthogonal decomposition (SPOD) data-driven methods linear stability analysis (LSA) physics-based, operator-driven method examine detail. With DFT SPOD, two dominant modes found inside tube. Likewise, LSA reveals distinct instabilities single-helical double-helical shape, which agree with findings SPOD terms spatial shape temporal frequency. A particular focus laid upon region upstream An adjoint-based sensitivity that both instability highly sensitive mean flow modifications transitional segment between runner tube, such induced by passive control devices. knowledge these sensitivities will guide an optimized design controlling mode.