Hydrodynamics of cavitating and vortical flows in hydraulic turbomachines in off-design conditions: inception and mitigation

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The working principle of turbomachines, based on generating or extracting swirl, is a fertile ground for the development of vortices and flow instabilities. Those structures take the form of vortices, cavitating regions, and periodic flow separations. Examples are cavitating inter-blade channel vortices or rotating stalls. They generally induce pressure fluctuations that can either locally damage the runner or cause dangerous oscillations of the entire hydraulic circuit. Most of the time, those damaging flow phenomena occur in off-design conditions. The rationale for studying off-design conditions stems from the need to increase the operating range of hydraulic turbomachines to enable finer modulations of energy demands versus production. For hydraulic turbines, the introduction on electrical grids of large quantities of random energy sources such as solar and wind translates into more time spent in off-design conditions. Hence developing mitigation strategies of damaging flow structures in off-design operation will improve the reliability and efficiency of hydraulic turbomachines. Using experimental facilities and numerical tools of the Hydraulic Machine Laboratory of Laval University (LAMH), the research program “Hydrodynamics of cavitating and vortical flows in hydraulic turbomachines in off-design conditions: inception and mitigation” intends to study and develop mitigation strategies of damaging flow structures in hydraulic turbomachines based on parametrization of their inception mechanisms through measurements and simulations on reduced-scale models. The long-term objectives of the research program are to: Identify and parametrize inception mechanisms of damaging flow structures in turbomachines for off-design conditions using specialized reduced-scale models. Develop Reduced-Order Models representing the inception dynamics of those structures. Study and develop efficient mitigation strategies. The first five years of the program will focus on columnar vortex array in no-load conditions of hydraulic turbines and vortex-related cavitation surge present in hydraulic pumps and turbines. Studies will be initiated to identify the tools required to build the Reduced-Order Models of the columnar vortex array. Reduce-Order Models will eventually provide tools to improve flow analysis and develop efficient mitigation strategies. Scientific contributions from the short-term objectives will be detailed descriptions of the inception mechanism of the columnar vortex array, the evaluation of the mass flow gain factor and cavitation compliance for full-load cavitation surge and, novel analysis methods for industrial flows based on POD and DMD. Importantly, this proposal will lead to 15 new Highly Qualified Personel with training in active research domains such as deep learning, computer vision, advanced flow measurements, and analysis.