Rediscovery Of A Special Type of Separation Pier · Sedimentation tank Gate Initial Situation: Best...
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Design of Separation Piers 4 1 7 0 , c , ≤ ≤ a) Type Gabrecht and Wittmann b) Type Rouvé (with design rules): c-e) Realized Special types f) Patent after model test based on model tests c) d) e) f) At low head river hydropower plants the optimal flow to the turbines is of great importance for maximum power production. Specially in the case of bay power plants, the flow must be redirected toward the turbine inlet. In order to minimize loss free as possible, great attention is put on the design of the separation pier. In the literature only a few design rules can be found. Optimal geometries are mainly found by model tests. In the course of full model tests of a projected bay power plant, a special pier type was rediscovered as the best design solution for inflow optimization. Rediscovery Of A Special Type of Separation Pier Michael Pucher and Peter Tschernutter Scientific questions • influence of pier, inlet and trash rack on the flow characteristic • impact of flow characteristic on power production • best and economic type of pier, inlet and trash rack • design rules and constructive recommendations Goals • establishment of underlying physical behavior in models and in nature • clarification of the impact of flow characteristic on power production • verification or rejection of existing design formulas • design rules and design recommendations Approach • literature study • investigation of existing structures • model tests Summary • Experience with hydraulic characteristics • Design is sophisticated process • Existing design formula not practicable for today´s design • Power output only indirect criteria Outlook • Further tests with • different river and bay geometries • Different pier and guidance wall geometries • Parallel numerical investigations • Measurements at existing structures 1 2 3 4 5 6 7 8 1 Generator bulb 2 Turbine 3 Draft tube 4 Trash rake 5 Power house 6 Penstock 7 Pool 8 Tailwater Magnitude of energy losses and electric power equation Generator Transmission Own Consumpt. N H g Q p P ⋅ ⋅ ⋅ ⋅ = η Mech./Electr. Losses lm Upper Res. Trash rake/Intake Turbine Inflow Low. Res. Hydr. Losses hv1 Outflow Losses hv2 Potential Energy HP Netto Energy HN P….Electric Power [MW] η….Overall efficiency η=100%-lm p....Density of water [kg/m³] g….Gravity [m/s] Q….Water Flow [m³/s] HN…Netto energy height [m] HN = HP-hv1-hv2 Requirements and Criteria a) General criteria of turbine makers - per centage criteria - flow direction - vortices b) Criteria of Fisher and Franke c) Velocity head correction factor (α - Value) d) Mean gravity of horizontal flow component ∫ ⋅ + ⋅ ⋅ = = A theor , kin real , kin dA ) v v ( A ³ v E E 3 1 Δ α Built piers of e.on (left) and RWE (right) The chosen model scale was 1 : 40 in accordance with Froud´s Law, which resulted in a maximum design flow of 20 l/s for two turbines. The resulting inflow conditions were evaluated qualitatively using strings visualizing flow conditions. Qualitative performance evaluation could be achieved by examining velocity (v) distributions. The width of the separation pier could not be increased, as calculated according to [Rouvé]; therefore only slight improvements could be obtained with standard pier geometries. Finally, only special solutions with additional guidance walls in front of separation piers resulted in acceptable inflow conditions to the turbines. Up to a point all guidance walls/split pier solutions resulted in similar performance. In further tests it became apparent that the position of the guidance wall is the dominating factor. The physical model tests were performed in a temporary flume of approximately 25 m length and 3,75 m width in the institute’s own laboratory. These distributions, derived from a 10 x 10 raster at each turbine intake was evaluated according to the Fisher & Franke (F&F) criteria and the alpha value. By using different criteria it was possible to order the alternatives according to the quality of the inflow conditions. The original design showed unfavorable inflow conditions into and at the turbine next to the weir. In a set of model tests first the intake shape was changed and then the separation pier geometry was varied. Model sight (above) Section trough penstock with Measuring section and 10x10 raster (lower left). Hydrometric vane (lower right) Legend River bed Rip rap Model wall Sedimentation tank Gate Best Alternative Initial Situation: Isotach field Turbine 2 Isotach field Turbine 2 QI QII QIII QIV QI QII QIII QIV Ranking of alternatives Original Rank Pier setting α- value upper bound lower bound Geometry • Several possible designs • Designs with split pier/guidance wall dominate - Good with one or two turbine flow - Less dependent on discharge 5 2 Q c B ⋅ = Flow around pier Longitudinal Flow downwards Step towards bottom of inlet Vortices Longi t udinal vor ti ces effects cause Vortex loss Trash rack loss Turbine loss consequence Over flow Angled flow Parallel Flow backflow Trash rack area unused flawed pier design Trash rack blockage Trash rack evenly used Even inflow even velocity profile uneven velocity profile Unused areas Trash rack Power house Separation pier Weir detachme nt vortex 7 5 1 Upp. Bound +/- Low. Bound +/- Area “in” = positiv Area “out” = negativ [% Area] Quadr. +/-10% vm T1 T2 WFA Flow direction 330,80 max. pool M e as u r em e nt s e ct ion Turbine blade section
Transcript of Rediscovery Of A Special Type of Separation Pier · Sedimentation tank Gate Initial Situation: Best...
Design of Separation Piers
4170 ,c, ≤≤
a) Type Gabrecht and Wittmann b) Type Rouvé (with design rules):
c-e) Realized Special types f) Patent after model testbased on model tests
c) d) e) f)
At low head river hydropower plants the optimal flow to the turbines is of great importance for maximum power production. Specially in the case of bay power plants, the flow must be redirected toward the turbine inlet. In order to minimize loss free as possible, great attention is put on the design of the separation pier. In the literature only a few design rules can be found. Optimal geometries are mainly found by model tests. In the course of full model tests of a projected bay power plant, a special pier type was rediscovered as the best design solution for inflow optimization.
Rediscovery Of A Special Type of Separation Pier Michael Pucher and Peter Tschernutter
Scientific questions
• influence of pier, inlet and trash rack on the flow characteristic
• impact of flow characteristic on power production
• best and economic type of pier, inlet and trash rack
• design rules and constructive recommendations
Goals
• establishment of underlying physical behavior in models and in nature
• clarification of the impact of flow characteristic on power production
• verification or rejection of existing design formulas
• design rules and design recommendations
Approach
• literature study
• investigation of
existing structures
• model tests
Summary
• Experience with hydraulic characteristics
• Design is sophisticated process
• Existing design formula not practicable for today´s design
• Power output only indirect criteria
Outlook
• Further tests with
• different river and bay geometries
• Different pier and guidance wall geometries
• Parallel numerical investigations
• Measurements at existing structures
1
23
4 5
6
7
8
1 Generator bulb2 Turbine
3 Draft tube
4 Trash rake5 Power house
6 Penstock7 Pool
8 Tailwater
Magnitude of energy losses and electric power equation
GeneratorTransmissionOwn Consumpt.
NHgQpP ⋅⋅⋅⋅=η
Mech./Electr. Losses lm
Upper Res.
Trash rake/Intake
Turbine
Inflow
Low. Res.
Hydr. Losses hv1
Outflow Losses hv2
Po
ten
tia
l E
ne
rgy H
P
Nett
oE
nerg
y H
N
P….Electric Power [MW]η….Overall efficiency
η=100%-lmp....Density of water [kg/m³]g….Gravity [m/s]Q….Water Flow [m³/s]HN…Netto energy height [m]
HN = HP-hv1-hv2
Requirements and Criteria
a) General criteria of turbine makers
- per centage criteria
- flow direction
- vortices
b) Criteria of Fisher and Franke
c) Velocity head correction factor (α - Value)
d) Mean gravity of horizontal flow component
∫ ⋅+⋅⋅
==A
theor,kin
real,kin dA)vv(A³vE
E 31∆α
Built piers of e.on (left) and RWE (right)
The chosen model scale was 1 : 40 in accordance with Froud´s Law, which resulted in a maximum design flow of 20 l/sfor two turbines. The resulting inflow conditions were evaluated qualitatively using strings visualizing flow conditions. Qualitative performance evaluation could be achieved by examining velocity (v) distributions.
The width of the separation pier could not be increased, as calculatedaccording to [Rouvé]; therefore only slight improvements could be obtained with standard pier geometries. Finally, only special solutions with additional guidance walls in front of separation piers resulted in acceptable inflow conditions to the turbines. Up to a point all guidance walls/split pier solutions resulted in similar performance. In further tests it became apparent that the position of the guidance wall is the dominating factor.
The physical model tests were performed in a temporary flume of approximately 25 m length and 3,75 m width in the institute’s own laboratory.
These distributions, derived from a 10 x 10 raster at each turbine intake was evaluated according to the Fisher & Franke (F&F) criteria and the alpha value. By using different criteria it was possible to order the alternatives according to the quality of the inflow conditions. The original design showed unfavorable inflow conditions into and at the turbine next to the weir. In a set of model tests first the intake shape was changed and then the separation pier geometry was varied.
Model sight (above)Section trough penstock with Measuring section and 10x10 raster (lower left). Hydrometric vane (lower right)
Legend
River bed
Rip rap
Model wall
Sed
ime
nta
tion
tan
k
Ga
te
Best AlternativeInitial Situation:
Isotach field Turbine 2 Isotach field Turbine 2
QI QII
QIII QIV
QI QII
QIII QIV
Ranking of alternatives
Original
Ran
k
Pie
r
setting
α-
va
lue
upper
bound
lower
bound
Geometry
• Several possible designs
• Designs with split pier/guidance wall dominate
- Good with one or two turbine flow
- Less dependent on discharge
52QcB ⋅=
Flow around pier
Longitudinal Flow downwards
Step towards bottom of inlet
Vortices
Lo
ng
itud
inal v
ortic
es
effects
cause
Vortex lossTrash rack
loss Turbine loss
consequence
Over flow
Angled flow
Parallel Flow
backflow
Trash rack area
unused
flawed pier design
Trash rack
blockage
Trash rack evenly used
Even inflow even velocity profile
uneven velocity profile
Unused areas
Trash rack
Power house
Separation pier
Weir
detachment
vortex
7 51
Upp. Bound +/-
Low. Bound +/-
Area “in” = positiv
Area “out” = negativ
[% Area]
Quadr.+/-10%
vm
T1 T2 WFA
Flow direction
330,80 max. pool
Measu
rem
en
t secti
on
Tu
rbin
e b
lad
e
sectio
n
