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

Virtual hydraulic laboratory, developed in collaboration with turbine manufacturer

byJacek SwiderskiSwiderski Engineeringwww.secfd.com, Ottawa, Canada

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.

Computational Fluid Dynamics (CFD) already established its strong presence in the hydropower industry as trusted engineering tool.

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 dimension component

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.

 

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.

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 tube2)     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 solver4)     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

Modification of the stay vanes position resulted in 8% increase of energy production

Upgrades implementedSpiral Case Kaplan Unit – stay vanes replacement

Clark Falls ProjectExpectd performance curve

Hnet = 41 ft

76%

77%

78%

79%

80%

81%

82%

83%

84%

85%

86%

87%

88%

89%

90%

91%

92%

93%

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6

Turbine Output [MW]

Eff

icie

ncy

[%

]

Efficiency (index test 1987)

adjusted CFD results (original blade)

adjusted CFD results (new blade)

Expected new efficiency curve

Upgrades implementedSemi-spiral Case Kaplan Unit – blades replacement

OLD NEW

Hnet = 41 ft

Generator output = 3000 kW

Courtesy of

NORCAN hydraulic turbine inc.

Courtesy of

NORCAN hydraulic turbine inc.

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.

Upgrades implemented Francis turbine – runner replacement

Courtesy of

NORCAN hydraulic turbine inc.

Hnet = 105m

Output before the upgrade = 4500 kW

Output after the upgrade = 5200 kW

(only runner replaced)

CFD diagnostics Classical Kaplan – erosion on the throat ring

Tracking reason for cavitation

CFD diagnosticsClassical Kaplan – leading edge tip: reasons for erosion

Bad inflow conditions on one side of the runner and very good on the other side

CFD diagnostics Semi - Spiral Case Kaplan Unit