Transcript Axial Flow turbine development for Ultra Low

Recent approach to refurbishments of small
hydro projects based on numerical flow analysis
by
Jacek Swiderski
Swiderski Engineering
www.secfd.com, Ottawa, Canada

Computational Fluid Dynamics (CFD) already
established its strong presence in the hydropower industry
as trusted engineering tool.

Virtual hydraulic laboratory, developed in collaboration
with turbine manufacturer

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 ?
(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)
2)
-
3)
4)
5)
-
Numerical model – full geometry of the turbine including
Intake
Spiral casing
Distributor (all stay vanes and wicket gates)
Runner
Draft tube
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.
CFD analysis – flow solver
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
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
Spiral Case Kaplan Unit – stay vanes replacement
Modification of the stay vanes position resulted in 8% increase of energy production
Upgrades implemented
Semi-spiral Case Kaplan Unit – blades replacement
Hnet = 41 ft
Generator output
= 3000 kW
Clark Falls Project
Expectd performance curve
Hnet = 41 ft
93%
92%
91%
90%
89%
88%
Efficiency [%]
87%
86%
85%
84%
83%
82%
81%
80%
79%
Efficiency (index test 1987)
adjusted CFD results (original blade)
78%
77%
adjusted CFD results (new blade)
Expected new efficiency curve
76%
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]
OLD
NEW
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
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 Kaplan – erosion on the throat ring
Tracking reason for cavitation
CFD diagnostics
Classical Kaplan
–
leading edge tip: reasons for erosion
CFD diagnostics
Semi - Spiral Case Kaplan Unit
Bad inflow conditions on one side of the
runner and very good on the other side