Date of Degree
MS (Master of Science)
The purpose of this thesis was to perform a comprehensive evaluation of proposed sluiceway deflectors in Hells Canyon Dam with the use of Computational Fluid Dynamics (CFD). A CFD model developed and validated by Politano et al. (2010) was used to assess the downstream performance of the deflectors. Relative performance is measured by effects of the deflectors on the flow field, Total Dissolved Gas (TDG) production, and probability of mechanical fish injury.
The deflectors evaluated in this model included the deflector with dimensions determined from a physical model as well as three additional deflector geometries that adjusted elevation, length and transition radius based on the physical model deflector. Physical model testing, at a 1:48 scale, of deflectors on Hells Canyon Dam performed by Haug and Weber (2002) provided a baseline deflector for the deflectors modeled in this study. The physical model was built and tested by the IIHR Hydroscience and Engineering.
The performance study that this thesis focuses on was performed at two different tailwater elevations, established with two different total river flowrates of 25 kcfs and 45 kcfs. Each deflector was evaluated considering the spillway jet regime, tailrace flow pattern, and total dissolved gas (TDG) production. According to the model, decreasing the deflector length or increasing the transition radius results in more TDG production at all tailwater elevations. At 45 kcfs, the height of the deflector does not appreciably affect the spillway jet regime or the TDG distribution in the tailrace. However, increasing the deflector elevation at this river flow increases the amount of powerhouse entrainment and induces a recirculation in the western region of the tailrace. The baseline deflector performed best because it had the smallest impact on the tailrace flow pattern and produced the least TDG.
The performance of the selected deflector was further evaluated for additional river flow rates of 37 kcfs, 45 kcfs and a 7Q10 flow condition of 71.5 Kcfs, with the 7Q10 condition being tested with and without the deflector. Although the deflector was able to prevent the spillway flow from creating a large amount of downstream TDG the 7Q10 flow condition significantly increased the TDG values downstream of the deflector relative to the other tested conditions. With the chosen deflector TDG values returned to forebay levels after 1 and 3.5 miles for the 37 kcfs and 45 kcfs river flowrates, respectively. With the deflector installed the 7Q10 flow condition creates considerable TDG production however the deflectors are able to reduce TDG production by 10% from the test without a deflector installed.
For all evaluated river flows, with the chosen deflector, entrainment from the powerhouse is observed in the simulations; this entrainment is caused by the sluiceway surface jets. As powerhouse flow increases there is an observed decrease in entrainment. This is due to the increase of flow velocity in the streamwise direction, or perpendicular to the direction of entrainment. An important western recirculation that is prominent in the 7Q10 flow condition is also caused by the introduction of deflectors onto the spillways. Reversed flows near the fishtrap region and water directed back into the aerated section of the spillway are consequences of this recirculation. The effect causes a 25% percent increase of entrained flow relative to the no deflector 7Q10 flow.
Injury of fish traveling over the spillway and through the sluiceway was estimated with the use of inert spherical particles and the computed flow field. Acceleration and strain experienced by the particles was calculated over the length of the spillway region. Numerical results were compared against literature values published by Deng (2005). Including the deflectors in the design increases the probability that fish will be injured. The most extreme cases of fish injury probability were 37 kcfs and the 7Q10 kcfs flowrates. For these cases, injuries experienced by the fish were 10% and 3% for minor and major injuries respectively. With comparison of the 7Q10 flows it appears that the inclusion of the deflector increases the induced minor injury induce from 5% to 10% and the major injury from 1% to 3%.
Fish tailrace residence time was calculated using inert particles introduced to the computed fluid flow field. These particles were tracked for 650 feet past the sluiceway inlets and their time to completion was recorded. Particles were released from the sluiceways as well as the powerhouses for the 37 kcfs, 45kcfs and 7Q10 flow conditions. Particles released from the sluiceways reduced in residence time with an increase in sluiceway flowrate. With some amount of powerhouse entrainment increasing the residence time of the particles released from the powerhouse. These particles follow the entrainment to the deep low velocity region in the stilling basin. As the lateral flow increases some of the particles released from the spillway will join the high speed jets produced by the deflectors and their residence time will be reduced. According to the model, deflectors consistently reduce overall residence time and are therefore not expected to increase fish migration time.
Water surface elevation near the fishtrap was measured for the 25 kcfs, 37 kcfs, 45 kcfs and 7Q10 flow conditions. The wave height near the fishtrap for the 7Q10 deflector case was predicted to be about one foot above the estimated water surface elevation. According to the model the inclusion of the deflector reduces the wave height.
Deflectors, Hells Canyon, TDG, Total Dissolved Gas
x, 162 pages
Includes bibliographical references (pages 160-162).
Copyright 2013 Michael Joseph Carbone