Numerical design methodology for reversible Deriaz turbine with high energy performance and reduced fish impacts

Abstract

The increased interest for further exploitation of hydropower and pumped hydro storage sites of lower head and capacity, and the tightening on the other hand of the environmental terms and restrictions, would require the design of corresponding hydro turbines and reversible machines with improved environmental performance. This work presents a numerical methodology to optimize the design of a Deriaz turbine in order to achieve high energy efficiency and improved fish friendly behaviour in both pump and turbine operation modes. Various numerical simulation and optimization software and tools are used, while the geometry of the machine is fully parameterized to allow for wide design modifications and corresponding numerical tests. At first, the most important design parameters and their variation range limits are identified by a sensitivity study. Next, several multi-objective optimization procedures are carried out, using general quantitative targets for a comparative evaluation of the various machine runner designs. The results show a complex interdependence or competitiveness of the machine efficiency and the various fish impact performance indices that requires careful analysis. The developed and applied methodology can produce one or more candidate designs that satisfactorily meet all the desired objectives.

Simulating Fish Motion through a Diagonal Reversible Turbine

“…An optimized reversible diagonal turbine has been the focus of the present investigation. The design has been a result of optimization, as discussed in previous publications by the authors [20]. The design features a five-bladed rotor and two series of stator blades, an outer one with 17 blades and an inner one with 20 blades.…”

“…Three layers of prismtype cells are included at all wall boundaries to capture near-wall gradients. The total computational mesh consists of 2.3 million cells, as demonstrated by a mesh-independence study conducted through prior work of the authors [20].…”

“…In this histogram, a comparison of turbine mode and pumping mode operation is shown. Forces between [20,400] N are much more probable in pumping mode, whereas forces between [400, 1000] N are somewhat more pronounced in turbine mode. However, in the latter case they represent a tiny fraction of samples, nearly 0.5%.…”

“…The study of a reversible, diagonal-type (Deriaz) turbine in both turbine and pumping modes. The model under consideration is a five-bladed turbine previously optimized in its energy recovery characteristics [20]. Diagonal turbines could be considered an advantageous solution compared to relatively low-head Francis turbines in sites with significant flow rate variation or when variable operation and flexibility are desired, thanks to their double regulation feature, as well as when the survivability of the passing fish is an important environmental issue, thanks to the mixed flow design and the smaller blade numbers of the runner.…”

State of the Art in Designing Fish-Friendly Turbines: Concepts and Performance Indicators

“…A recent variant [108] to the more computationally expensive 6-DoF techniques decouples the flow field from the body tracking. This decoupling makes it possible to solve the flow field with steady-state moving reference frames, which greatly speeds up the solution by roughly two orders of magnitude, allowing for the derivation of statistics (see indicatively Figure 10, where a specifically designed reversible, fish-friendly Deriaz turbine [109] was tested). Since the flow is decoupled from the body motion, the pressure field around the moving body is approximated through the dynamic pressure of the slip velocity.…”