Investigation of Efficient Optimization Approach to the Modernization of Francis Turbine Draft Tube Geometry

Abstract

The installation of new and revitalization of existing hydropower requires the optimal design of hydraulic turbine parts, which were previously mostly based on simplified analytical methods and engineering practices. With the increase in computational power, optimization methods now present an effective approach to the improvement of the geometry of turbine parts, thus enabling fine geometry-tuning adjustments of site specifics. However, despite continually increasing computational power, such numerical optimizations still require substantial resources and time. Therefore, in the proposed paper, extensive analysis of different numerical simplifications was conducted to determine the best trade-off between accuracy and the required computational resources for draft tube optimization. Additionally, the influence of geometry parametrization in terms of greater geometry flexibility, different goal functions, and optimization parameters was investigated. Within the considered constraints, a novel draft tube geometry was obtained, with the elbow displacements toward the draft tube exit, a shape that could not be obtained with the usual draft tube parametrization. It was also observed that geometry improvements for a single operating point did not provide improvements for other operating points. The obtained findings regarding the numerical and optimization setup can be used as guidelines for future optimization research, where multiobjective optimization for multiple operating points should be further investigated.

Optimization of Elbow Draft Tubes for Variable Speed Propeller Turbine

“…The velocity field at the exit from the runner is often taken from a detailed CFD simulation of the entire turbine with the primary conical draft tube due to the limited computing resources. Several authors confirm the reliability of this method for optimisation [11,14,16].…”

“…Other papers deal with the minimization of hydraulic losses in EDT. A combination of those attitudes is most frequent [11,12]. Our article uses a modified c p criterion, which we call the pressure regeneration efficiency η p (Equation ( 2))-our main output parameter.…”

“…Steady-state RANS calculations are still the only way to offer relatively high-quality results with less computational effort [9]. Most authors optimize DT for the operation of the given turbine unit-for a single operation point [11][12][13] or for multiple operation points [14]. The key for multiple operation points optimization, is to assign weight to each operating point, which is understandable for optimisation where hydrological parameters are known.…”

Influence of Runner Downstream Structure on the Flow Field in the Draft Tube of a Small-Sized Water Turbine

“…Changing the draft tube structure is mainly achieved by changing the profile and adding grooves [21][22][23]. Changing the diffusion section of the draft tube to an inclined cone can eliminate vortex strips, reduce flow instability, disrupt the development of strong swirls, and reduce related pressure fluctuations [24,25].…”