Undercurrent: The Alden Blog

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Industrial fluid dynamics insights


Eel Shining to Locate Upstream Passage Routes
Searching for eels is an activity reserved for those who like to stay up late. Only under the cover of darkness is one able to have the best chance to find these nocturnal fish. Surveying for American eels, Anguilla rostrata, with lanterns at night or “shining” is a common method to document their presence in rivers across eastern North America. Juvenile American eels often congregate downstream of obstacles that block their upstream movement (eels are catadromous fish, meaning adults spawn in saltwater and the young move into freshwater to rear and mature before returning to the marine environment to complete the reproductive cycle). Hydroelectric dams are common impediments to upstream migrants along river courses. Finding optimal areas to establish passage routes for eels to move upstream is a primary reason to shine for eels.  Eels, being a fish, become more active as the water temperature rises. When the temperature is above 10 degrees C, which generally occurs from May to October in New England, eels of all ages and sizes become more active. The recently born glass eels, (so called ...

Energy Dissipating Devices: Total Dissolved Gas Production at High Head Dams - Part 3
In Parts 1 and 2 of this series we talked about production of total dissolved gas (TDG) at high head dams, and the use of air supply systems to mitigate cavitation damage to spillways and spillway modifications. In this part, we’ll discuss the structural designs used to reduce TDG during flow release from spillways. Super-cavitating roughness elements, or baffle blocks for short, are designed to break up flow as water travels down a spillway. Depending on the placement of the blocks on the spillway surface, they can also help spread out the jet of water laterally as it exits the spillway, resulting in a larger impact area on the tailrace. Why does this help reduce TDG production? As we discussed in Part 1, dissolved gas supersaturation in the tailrace is a function of how long it takes the bubbles from the aerated flow to reach the water surface. By spreading out the impact zone of the spillway jet, and decreasing the amount of energy the jet has, plunge depth of the jet is reduced and the aerated flow can rise ...

Takeaways from the Alden Forum 2017: Hydropower and Fish Passage
On May 17-18, Alden hosted a forum on hydropower and fish passage that was attended by more than 45 industry, state and federal agency, and NGO representatives.  The forum focused on fish passage issues typically encountered at projects in the Northeast and Southeast U.S.  It was particularly timely because the relicensing of 231 hydropower projects will occur throughout the U.S. between 2018 and 2025, with an additional 100+ projects to be relicensed between 2026 and 2030.  More than half of these projects are located in the Northeast and about 30% are located in the Midwest and South.  All of the projects will need to address a variety of environmental issues associated with their operation and, in many cases, mitigation alternatives will need to be developed to reduce or minimize impacts to affected resources.  The two most prevalent environmental issues addressed during relicensing typically are instream flows and fish passage.  Fish passage can be problematic with respect to biological, engineering, and project operation considerations. It can also be very costly.  Based on these issues, the goal of the Forum was ...

Fluid Dynamics Hobbies IV: Archery
For many employees at Alden, fluid dynamics is part of their life outside the office--in the sports they choose for their free time.  In many cases, a sport was what came first and later helped inform a career choice in fluids and fluid flow.  This ongoing series features some of the various and unique ways our employees spend some of their non-working hours and how CFD and fluid flow analysis is being used to improve techniques used in those sports.   Part IV: Archery - Duncan Phyfe   Duncan Phyfe, a senior CFD engineer at Alden, started enjoying archery thanks to his mother.  She was one of the riflery coaches at Choate-Rosemary Hall prep school.  When the school needed an archery instructor, they assumed she could do it, since she already knew how to get one type of projectile to hit a target!  So Duncan has been shooting arrows since he was about 6 years old.   When Duncan was 10 years old, he started attending The World Archery Center (TWAC), and that is when he started to learn the physics and aerodynamics of archery. ...

Fluid Dynamics Hobbies III: Whitewater Kayaking
You might never know when one seemingly minor decision could change your life. One summer weekend, just before entering my third year in the Civil & Environmental Engineering program at Tufts, I found myself on a whitewater kayaking class for beginners run by volunteer instructors with the Appalachian Mountain Club. A friend recruited me to join at the last minute; they needed more new “boaters” to reach their minimum capacity. Some combination of perfect weather, good company, and new challenges that weekend got me hooked on the sport. The more time I spent on the river, the more folks I met who had degrees and careers related to hydrology or engineering. That would eventually include me, too – my love for this hobby & fluid dynamics led me to work here at Alden. When I returned to school in the fall, I took my first fluid dynamics course. The coursework and the new hobby complemented each other – spending time in a boat made it easier for me to understand certain fluid mechanics topics. One of those topics is ...

Takeaways from the Association of State Floodplain Managers Conference
Testing of Flood Control America’s One World Trade Center flood protection barrier at Alden During the first week in May, I attended the Association of State Floodplain Managers (ASFPM) Conference in Kansas City.  This conference is generally recognized as the key floodplain conference in the U.S. In addition to floodplain managers, associated consulting firms and product vendors regularly attend. We thought it would be a good idea to go, given Alden’s recent activity in flooding related testing and modeling.  Given the nature of my interest, I primarily attended sessions on floodproofing and modeling, and also spent time in the exhibit.  The sessions were well attended and had good quality presentations. For me, the key takeaways from the conference were:   In general, insurance companies shouldn’t be expected to invest in protecting areas from flooding.   Jonathan Goldstick from CH2M gave an excellent presentation on a study aimed at building flood barriers to protect Gowanus Canal and Newtown Creek water treatment plants in New York City from storm surge flooding.  When the City realized ...

Air Supply Ramps and Cavitation: Total Dissolved Gas Production at High Head Dams – Part 2
Part 1 of this series outlined how high concentrations of total dissolved gas (TDG) can occur downstream from high head dams when their spillways are open, and how this TDG can be harmful or even fatal to fish. Alden has been involved in several recent projects for which the objective was to reduce TDG downstream of high head dams. Alden performed the hydraulic and structural design of roughness elements that break up the high velocity jet of flow discharged from the spillway. TDG production is reduced by these roughness elements because they cause the jet to spread out and thereby reduce the plunge depth in the receiving water, which reduces TDG. The roughness elements work very well at reducing plunge depth, but they can cause cavitation, which can damage the spillway surface and the blocks themselves. The design and implementation of the roughness elements will be topic of another article. The present article focuses on reducing the potential for cavitation on the roughness elements. Alden designed roughness elements have been installed on spillways at Cabinet Gorge and Boundary Dams. Cabinet ...

The Economics of Hydro Turbine Performance Testing
Today’s entry comes from a guest blogger, Jim Walsh, President of Rennasonic, a small consulting firm specializing in turbine and pump performance testing and optimization of multi-unit hydroelectric power plants using ultra-sonic multi-path flow meters.  Alden has partnered with Rennasonic for numerous turbine performance tests, providing supplemental flow measurements using dye dilution and current meter profiling. Power output, flow, and head measurements being taken during performance testing As a hydropower electric power generating utility, how do I know when I should, or should not, invest in my equipment?  The answer can be complicated due to many factors, including but not limited to: the current price of power, generating capacity, equipment age, and government regulations.  To determine the performance of an installed hydropower turbine, the measurements of water flow, head, and power must be made within a reasonable amount of uncertainty.  Generally speaking, flow is the most difficult parameter to measure in the field and, consequently, is the most expensive.  The cost of measuring flow can seem unsurmountable for small hydropower owners, so the question becomes when testing expenditures yield a ...

Fluid Dynamics Hobbies II: Sailing
For many employees at Alden, fluid dynamics is part of their life outside the office--in the sports they choose for their free time.  In many cases, a sport was what came first and later helped inform a career choice in fluids and fluid flow.  This ongoing series will feature some of the various and unique ways our employees spend some of their non-working hours and how CFD and fluid flow analysis is being used to improve techniques used in those sports. Part II: Sailing - Dave Schowalter and Kimbal & Becca Hall Sailing is all about using fluid dynamic forces to propel and control a boat.  There is the fluid dynamics of the water against the rudder and the keel or centerboard, which allows the skipper to steer the boat and and to sail upwind.  Then there is the aerodynamics of the wind against the sails, and maximizing the lift on the sails.  As with an airplane, balancing the fluid dynamics forces is a key element to boat design and making a boat responsive and easily controllable. At least three current Alden ...

Improving Water Quality: Total Dissolved Gas Production at High Head Dams – Part I
During spill season at hydroelectric dams, more water flows into the upstream reservoir than can be used to generate electricity in the powerhouses. This excess flow must pass through a number of different flow release structures in order to bypass the dam and powerhouse. Spillways, diversion tunnels, and low-level sluice gates are commonly used to route flow past dams. Open channel spillways are one of the most common flow release structures at high head dams, and create a highly aerated, turbulent jet of water that exits the spillway up to 150 feet above the river downstream of the dam. This waterfall of aerated flow can plunge to the bottom of the tailwater pool, where the bubbles of atmospheric gases are slowly dissolved into solution with the water. The deeper the jet plunges, the more pressure is exerted by the water on the bubbles, dissolving them faster and preventing them from rising to the surface. This is why we see a frothy white plume of flow that can stretch up to half a mile downstream of a dam when flow ...