This paper proposes an original approach to investigate the influence of the geometry of Francis turbines draft tube on pressure fluctuations and energy losses in off-design conditions. It is based on Design of Experiments (DOE) of the draft tube geometry and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The test case is a Francis turbine unit of specific speed Ns=120 m-kW which is required to operate continuously in off-design conditions, either with 45% (part-load) or 110% (full-load) of the design flow rate. Nine different draft tube geometries featuring a different set of geometrical parameters are first defined by an orthogonal array-based DOE approach. For each of them, unsteady and steady CFD simulations of the internal flow from guide vane to draft tube outlet are performed at part-load and full-load conditions, respectively. The influence of each geometrical parameter on both the flow instability and resulting pressure pulsations, as well as on energy losses in the draft tube, are investigated by applying an Analysis of Means (ANOM) to the numerical results. The whole methodology enables the identification of a set of geometrical parameters minimizing the pressure fluctuations occurring in part-load conditions as well as the energy losses in both full-load and part-load conditions while maintaining the requested pressure recovery. Finally, the results of the CFD simulations with the final draft tube geometry are compared with the results estimated by the ANOM, which demonstrates that the proposed methodology also enables a rough preliminary estimation of the draft tube losses and pressure fluctuations amplitude.
In general, Francis turbines are known to last for 40 to 50 years of use. However, exchanging an old turbine for a new is expensive because of modernization costs. Therefore, many modernization projects will take place through new runner changes. The Francis turbine in this paper has a high specific speed of about 330m-kW and a runner diameter of about 4.3m. The new runner can be expected to have a more stable flow and improved performance by flow analysis. In this paper, the performance analysis of the runner was performed using the CFD by Design Of Experiments (DOE). The sensitivity of variables was examined using L18 method. Numerical analysis was performed via BladeGen, Turbogrid, ICEM CFD, and CFX, which are commercial CFD codes. The design goal is to enable not only the best efficiency point but also a more stable operation than before even at partial load conditions. Find out how to find the shape of a runner blade by searching for design points that maximize annual power generation according to newly selected operating conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.