Canadian Dam Association Bulletin - Spring 2018 - 18

Figure 2 - Experimental Results of Orifice Head Loss Coefficient
vs Diameter Ratio (Zhang and Chai 2001)

installed from elevation 425 m up to 440 m.
Initially, the orifice tunnel design considered
passing 390 m³/s at a
reservoir level below
425 m; however, model
testing showed that the
wider operating range
increased cavitation
risk at higher reservoir
levels. The design basis
for the orifice tunnel

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assumed that no upstream regulation would be required; therefore, the
discharge through the orifice tunnel
would increase as the reservoir level
increased. Once the reservoir reaches
elevation 440 m the minimum downstream flows will be maintained by
the spillway low level outlets.

6. HYDRAULIC LOSSES
The first parameter used to define
the initial orifice sizing was the
hydraulic loss. The loss coefficient
for the orifices was assumed using
experimental data from Xiaolangdi
(Zhang and Chai 2001). The head loss
was documented as a function of the
orifice contraction ratio (β = d/D where
d = orifice diameter and D = tunnel
diameter). The head loss coefficient,
k, is defined according to the general
equation H L = k*v2/2g where HL =
head loss across the orifice, v = average velocity through the orifice and
g = gravitational acceleration. The
detailed geometry assumes that the
orifice will have an upstream radius
on the leading edge of r = 0.06 m
(Zhang and Chai 2001) and results
are shown both with and without an
upstream ring intended to improve
cavitation performance. The tunnel
diameters are similar for Xiaolangdi
(D = 14.5 m) and Site C (D = 10.8 m), so
the use of the model test head loss data
was thought to be applicable for initial
Site C design. The model scale that
served as the basis for the head loss
data presented in Figure 2 (Zhang and
Chai 2001) was 1:60 based on Froudescale similitude. The head loss coefficient for the Site C orifice layout was
later adjusted using project specific
physical hydraulic model test results.

7. CAVITATION COEFFICIENT
The second parameter used to
define the initial orifice sizing was
the cavitation coefficient ( ) (Zhang
and Chai 2001). Figure 3 presents the
experimental results of the cavitation
coefficient versus the orifice diameter
ratio for a specific set of orifice geometries. Figure 3 shows that the radius
on the upstream orifice edge and the
addition of the ring resulted in significantly reduced incipient cavitation
18
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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
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