Recent approach to refurbishments of small hydro projects based on numerical flow analysis

1. Recent approach to refurbishments of small hydro projects based on numerical flow analysis byJacek SwiderskiSwiderski Engineeringwww.secfd.com, Ottawa, Canada • Virtual hydraulic laboratory, developed in collaboration with turbine manufacturer • Computational Fluid Dynamics (CFD) already established its strong presence in the hydropower industry as trusted engineering tool. • Study and analysis of the results allow developing an upgrade strategy • Selected practical applications of Computational Fluid Dynamics (CFD) based on commercial CFX-TASCflow software package.

2. Why would older turbines need to be upgraded – would classical design methods be a reason ? (a)Aerodynamics theories adequate for a very limited range of water turbines (compressibility) (b)Existence of 3rd dimensioncomponent of the flow within the blade-to-blade space of a turbine runner (c) The upstream influence no classical, published design method takes it into account.

3. Design based on CFD verification Major design strategies exercised by the industry: A)Classical design approach: (i) model tests– modifications (loop: lab-shop) (ii) CFD analysis-model tests–modifications (loop:CFD-lab-shop) B)Newer approach – generic algorithms: model generation – CFD analysis – decision on shape modification (loop: CFD - Decision Program - CFD) C) Attempts to solve reverse problem: should there be a strict mathematical solution to the N-S equations,finding a shape of flow channel to achieve certain effect would be possible.

4. Practical methodology for an upgrade 1)Numerical model – full geometry of the turbine including -          Intake -          Spiral casing -          Distributor (all stay vanes and wicket gates) -          Runner -          Draft tube 2)Tune-up of the numerical model -          Grid quality: verification and refinement. Based on couple of runs of the flow analysis, the nodes distribution is adjusted according to the velocity/pressure field. -          Operating parameters. In the non-dimensional factors, the CFD results must be within a certain range from the field measurements. 3)CFD analysis – flow solver 4)Analysis of results -          Energy dissipation field (losses). -          Pressure gradients – estimate possibilities for cavitation -          Determination of the flow areas, where the velocity field has highest non-uniformity 5)Strategy for upgrade based on expected cost/benefit ratio -          Intake shape -          Distributor (wicket gates profile, stay vanes set-up) -          Runner design -          Draft tube shape

8. Upgrades implementedSpiral Case Kaplan Unit – stay vanes replacement Modification of the stay vanes position resulted in 8% increase of energy production

9. Upgrades implementedSemi-spiral Case Kaplan Unit – blades replacement Hnet = 41 ft Generator output = 3000 kW Courtesy of NORCAN hydraulic turbine inc. OLD NEW

10. Courtesy of NORCAN hydraulic turbine inc.

11. Upgrades implemented Francis turbine – runner replacement Hnet = 50m Generator output guaranteed = 1615 kW (was 1500 kW) Generator output achieved = 1725 kW Output increase: 15% Courtesy of NORCAN hydraulic turbine inc.

12. Upgrades implementedFrancis turbine – runner replacement Hnet = 105m Output before the upgrade = 4500 kW Output after the upgrade = 5200 kW (only runner replaced) Courtesy of NORCAN hydraulic turbine inc.

13. CFD diagnosticsClassical Kaplan – erosion on the throat ring Tracking reason for cavitation

14. CFD diagnosticsClassical Kaplan – leading edge tip: reasons for erosion

15. CFD diagnostics Semi - Spiral Case Kaplan Unit Bad inflow conditions on one side of the runner and very good on the other side