Recent approach to refurbishments of small hydro projects based on numerical flow analysis
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Recent approach to refurbishments of small hydro projects based on numerical flow analysis. by Jacek Swiderski Swiderski Engineering www.secfd.com, Ottawa, Canada. Virtual hydraulic laboratory , developed in collaboration with turbine manufacturer.

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


Why would older turbines need to be upgraded would classical design methods be a reason
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.


Design based on cfd verification
Design based on CFD verification classical design methods be a reason ?

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
Practical methodology for an upgrade classical design methods be a reason ?

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


Upgrades implemented classical design methods be a reason ?Spiral Case Kaplan Unit – stay vanes replacement

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


Upgrades implemented classical design methods be a reason ?Semi-spiral Case Kaplan Unit – blades replacement

Hnet = 41 ft

Generator output = 3000 kW

Courtesy of

NORCAN hydraulic turbine inc.

OLD

NEW


Courtesy of classical design methods be a reason ?

NORCAN hydraulic turbine inc.


Upgrades implemented classical design methods be a reason ? 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 classical design methods be a reason ?Francis 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.


CFD diagnostics classical design methods be a reason ?Classical Kaplan – erosion on the throat ring

Tracking reason for cavitation


CFD diagnostics classical design methods be a reason ?Classical Kaplan – leading edge tip: reasons for erosion


CFD diagnostics classical design methods be a reason ? Semi - Spiral Case Kaplan Unit

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


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