Canadian Dam Association Bulletin - Spring 2018 - 22

*

*

*

*

*

*

not impact the tunnel wall (see
Figure 7). No cavitation is expected
in this region based on PHM and
CFD pressure results. PHM and CFD
results also confirmed that the large
diameter bend does not impact flow
conditions at orifice #2.
The most downstream orifice will
be placed at the downstream limit of
the future tunnel plug. This ensures
the pressure in the tunnel downstream of the main dam centreline
is maintained at or below diversion
levels and will also assist with forming the downstream end of the tunnel plug after reservoir filling.
The spacing between the three
downstream orifices will be set at
five tunnel diameters as model testing showed that a spacing of three
diameters resulted in un-desired
interaction between orifices.
The diameter ratios of the orifices from orifice #1 to orifice #4
in sequence will be 0.68, 0.69,
0.72, 0.75.
The orifices will be formed entirely
of steel plate and infilled with concrete (see Figure 10). The tunnel
concrete liner will also be locally
thickened at each orifice location
to accommodate the thrust.
The discharge through the orifice tunnel will increase from
approximately 390 m³/s at elevation 425 m up to 535 m³/s at elevation 440 m based on PHM results
(CFD discharge measurements were
approximately 10% higher than the
PHM results).
Pressure results show that the
minimum crown pressure is
greater than 0 m (pressure head)
for all orifices except orifice #4

which has a minimum pressure
of −1.1 m +/− 1.0 m at the maximum
head/discharge condition. CFD pressure results were comparable with a
measurement of −2.2 m at the same
location as the PHM pressure tap.
The Site C diversion tunnel and orifice layout are presented in Figures 8,
9 and 10.

11. CAVITATION SCALING
A thorough review of references
from Xiaolangdi and discussions
with cavitation experts concluded
that scaling the cavitation coefficient
for the difference between model
and prototype size was required.
Extensive research and investigations were done with the final scaling assumptions taken from a book
written on the Xiaolangdi project in
Chinese (Lin 2003).
The theoretical cavitation plot
for the proposed Site C four orifice

arrangement is shown in Figure 11.
The following points describe how
the cavitation plot was developed
and define the lines and points
shown:
* The incipient cavitation index for
each orifice was calculated using
the methodology referenced for
Xiaolangdi (Zhang and Chai 2001)
using the orifice head loss coefficients measured in the Site C
PHM study.
* The "Incipient Cavitation - Model"
line represents the Xiaolangdi
model test results performed in a
vacuum chamber which identified
incipient cavitation with a model
tunnel diameter of 0.15 m (Zhang
and Chai 2001).
* A relationship between incipient cavitation and model scale
was developed by Lin (Lin 2003)
based on measurements of incipient cavitation in several different

Figure 8 - Diversion Tunnel Plan

Figure 9 - Diversion Tunnel Partial Section

Figure 7 - Plan view of velocities
downstream of orifice #1 (velocity in m/s)
22

Figure 10 - Orifice Cross Section
View past issues of the CDA Bulletin online at www.naylornetwork.com/cda-nxt/


http://www.naylornetwork.com/cda-nxt/

Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Spring 2018

Board of Directors
President’s Message
Site C Clean Energy Project Diversion Tunnel Orifices for Energy Dissipation During Reservoir Filling
Application for 2018 CDA Scholarships
CDA Presents 2017 Scholarships
ICOLD Corner
CDA Conference 2018
EIC Awards Gala
Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Spring 2018 - 1
Canadian Dam Association Bulletin - Spring 2018 - cover1
Canadian Dam Association Bulletin - Spring 2018 - cover2
Canadian Dam Association Bulletin - Spring 2018 - 3
Canadian Dam Association Bulletin - Spring 2018 - 4
Canadian Dam Association Bulletin - Spring 2018 - 5
Canadian Dam Association Bulletin - Spring 2018 - 6
Canadian Dam Association Bulletin - Spring 2018 - Board of Directors
Canadian Dam Association Bulletin - Spring 2018 - President’s Message
Canadian Dam Association Bulletin - Spring 2018 - 9
Canadian Dam Association Bulletin - Spring 2018 - Site C Clean Energy Project Diversion Tunnel Orifices for Energy Dissipation During Reservoir Filling
Canadian Dam Association Bulletin - Spring 2018 - 11
Canadian Dam Association Bulletin - Spring 2018 - 12
Canadian Dam Association Bulletin - Spring 2018 - 13
Canadian Dam Association Bulletin - Spring 2018 - 14
Canadian Dam Association Bulletin - Spring 2018 - 15
Canadian Dam Association Bulletin - Spring 2018 - 16
Canadian Dam Association Bulletin - Spring 2018 - 17
Canadian Dam Association Bulletin - Spring 2018 - 18
Canadian Dam Association Bulletin - Spring 2018 - 19
Canadian Dam Association Bulletin - Spring 2018 - 20
Canadian Dam Association Bulletin - Spring 2018 - 21
Canadian Dam Association Bulletin - Spring 2018 - 22
Canadian Dam Association Bulletin - Spring 2018 - 23
Canadian Dam Association Bulletin - Spring 2018 - 24
Canadian Dam Association Bulletin - Spring 2018 - 25
Canadian Dam Association Bulletin - Spring 2018 - Application for 2018 CDA Scholarships
Canadian Dam Association Bulletin - Spring 2018 - 27
Canadian Dam Association Bulletin - Spring 2018 - CDA Presents 2017 Scholarships
Canadian Dam Association Bulletin - Spring 2018 - 29
Canadian Dam Association Bulletin - Spring 2018 - ICOLD Corner
Canadian Dam Association Bulletin - Spring 2018 - 31
Canadian Dam Association Bulletin - Spring 2018 - CDA Conference 2018
Canadian Dam Association Bulletin - Spring 2018 - 33
Canadian Dam Association Bulletin - Spring 2018 - EIC Awards Gala
Canadian Dam Association Bulletin - Spring 2018 - 35
Canadian Dam Association Bulletin - Spring 2018 - 36
Canadian Dam Association Bulletin - Spring 2018 - 37
Canadian Dam Association Bulletin - Spring 2018 - Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Spring 2018 - cover3
Canadian Dam Association Bulletin - Spring 2018 - cover4
https://www.nxtbook.com/naylor/CDAQ/CDAQ0119
https://www.nxtbook.com/naylor/CDAQ/CDAQ0418
https://www.nxtbook.com/naylor/CDAQ/CDAQ0318
https://www.nxtbook.com/naylor/CDAQ/CDAQ0218
https://www.nxtbook.com/naylor/CDAQ/CDAQ0118
https://www.nxtbook.com/naylor/CDAQ/CDAQ0417
https://www.nxtbook.com/naylor/CDAQ/CDAQ0317
https://www.nxtbook.com/naylor/CDAQ/CDAQ0217
https://www.nxtbook.com/naylor/CDAQ/CDAQ0117
https://www.nxtbook.com/naylor/CDAQ/CDAQ0416
https://www.nxtbook.com/naylor/CDAQ/CDAQ0316
https://www.nxtbook.com/naylor/CDAQ/CDAQ0216
https://www.nxtbook.com/naylor/CDAQ/CDAQ0116
https://www.nxtbook.com/naylor/CDAQ/CDAQ0415
https://www.nxtbook.com/naylor/CDAQ/CDAQ0315
https://www.nxtbook.com/naylor/CDAQ/CDAQ0215
https://www.nxtbook.com/naylor/CDAQ/CDAQ0115
https://www.nxtbookmedia.com