Undercurrent: The Alden Blog

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Industrial fluid dynamics insights


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 ...

Fluid Dynamics Hobbies Part I: Synchronized Swimming
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 new and 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 1 - Synchronized Swimming - Amie Humphrey Facendola I have loved swimming and being in or on the water since I was very young.  I was fortunate enough to join the local synchronized swimming team in my early teens and the sport has played a significant role in my life.  I competed with the Synchro-Maids of Central Massachusetts for 6 years in middle/high school and again as a masters swimmer for 4 years after college. A love of water is the reason I chose the concentration of civil and environmental engineering in college and was one reason ...

Fluid-Structure Interaction: Sloshing
Sloshing is something that everyone is familiar with on a very basic level.  The classic example is trying not to spill a full cup of coffee – but I’ve had a similar experience with enthusiastic children at bath time.   The basic idea is that you have liquid in some sort of a container with a free surface.  When there is a force applied to the liquid – like walking with the coffee cup, or kids splashing around in the tub – the liquid starts moving.  The container confines the motion of the liquid, and sets up a back-and-forth oscillation, which we know as sloshing.   Spilling your coffee is usually just a minor inconvenience, but with larger containers sloshing can have real consequences.  Some bigger examples of sloshing include: Jet fuel sloshing inside the wing tank of an airplane. Harbors sloshing as a result of a tsunami (e.g. Hilo, Hawaii or Crescent City, CA). Large lakes sloshing as a result of a large storm. Tides sloshing in ocean ...

From Mountain Clouds to River Plumes: Observations and modeling of turbulent mixing in stratified flows
Mixing between fluids of different properties goes on all around us every day (e.g., think of stirring milk into your coffee or smoke billowing from a chimney).  In many flows of engineering relevance, velocity differences between fluid bodies generate turbulent motions that, in turn, greatly enhance the mixing process; small-scale chaotic eddies that characterize the turbulence are much more effective than molecular diffusion at mixing fluid properties such as momentum, heat, salinity, sediment load, or pollution concentration. When fluid bodies are of different densities the effects of gravity weigh heavily on the turbulent mixing process (pun intended).  For example, when warm air escapes from a chimney it accelerates upward in a turbulent billow because it is lighter (less dense) than the cooler air around it, and gravity acts to drive turbulence through buoyant convection.  On the other hand, in a stably-stratified lake, gravity acts to suppress turbulence at the thermocline where lighter, warm water overlies heavier cold water. The signatures of turbulent mixing in stratified flows are perhaps most obvious in the sky above us.  Clouds provide a convenient flow visualization ...

The Changing Energy Climate - Part II
In the last installment of this series, we discussed energy demand, energy supply, and the impact of the rapid growth of solar power on changing energy sources.  Today, we continue with the effects of power prices, the importance of power storage, and offer some conclusions. Price of Power A significant portion of the United States electricity markets is split into hubs.  Each hub is an independent energy market in which supply and demand set the price of electricity on a real time basis.   A map of United States hub zones is shown in the following figure. Daily electricity demand is primarily based upon the time of day and climate.  As shown in Part I, more electricity is used during daylight and evening hours than night time.  Very cold or very warm weather can add demand due to heating and cooling.  Additional constraints on fuel costs and available supply add an extra layer of complexity.  The cost of environmental mitigations for coal fired power plants, the lack of sufficient natural gas supply in certain markets like New England, and the recent addition ...

The Changing Energy Climate - Part I
As we discussed in our first blog post, there are many challenges facing the nuclear industry. One of the greatest is the current energy climate.  There are many contributing factors to the general state of flux in energy production, which we would like to explore today.  These challenges don’t just impact the nuclear industry, but also affect energy producers across generation types. Energy Demand It may surprise you, but US energy consumption has effectively plateaued over the last 15 years.  Below is a plot generated with the US Energy Information Administration Open Data Embedded Visualization Library.  The EIA provides a wide range of information and data products covering energy production, stocks, demand, imports, exports, and prices; and prepares analyses and special reports on topics of current interest. There are four sectors that are included when looking at total energy consumption.  These include Residential, Commercial, Industrial, and Transportation, all of which are shown in the figure.  As you can see, starting around the year 2000 the Total Energy Consumption has plateaued.  The largest changes in trends  have been experienced by the Industrial Sector, ...

NIAC Annual Meeting
In November 2016, the Alden Quality Assurance department attended the NIAC (Nuclear Industry Assessment Committee) annual meeting.  NIAC is the supplier equivalent to NUPIC (https://www.aldenlab.com/News/Blog/PostId/9/nuclear-procurement-issues-committee-annual-meeting) and the main benefit of membership is for suppliers to share audits of their sub-suppliers.  NIAC membership is open to suppliers with a 10CFR50 Appendix B or equivalent DOE quality program, and who demonstrate and agree to compliance with the NIAC Charter.  Alden joined NIAC in the fall of 2014 and the membership has helped reduce quality assurance costs while also staying in touch with current industry issues and maintaining a high quality product for our clients. The meeting was held in Jacksonville, Florida and featured the necessary business of setting the audit schedule for the upcoming year and providing auditor training.  The auditor training is important to ensure consistent and accurate audits that all members can share and rely on.  Additionally, there was a keynote address by Ben Marguglio of High Technology Seminars (http://hightechnologyseminars.com/).  Mr. Marguglio is a leading authority on human performance factors and human errors, including error prevention and reduction.  He ...