TOO CLOSE OR NOT CLOSE ENOUGH?
By Jeffrey Winters
Ranks of wind turbines turning in the breeze make an iconic image of the application of renewable energy. But the exact spacing of those turbines is coming under renewed scrutiny. The final outcome may determine just how much wind power can contribute to the international energy supply.
How exactly to calculate the land use involved in wind power production itself is a contentious issue. Many estimates, including those by wind power opponents, account for the entire area taken up by wind farms and even some land on the perimeter of the farm when determining the total land use. Others, who point out that the land under the turbines often continues to be used for farming or ranching, claim the actual footprint is much smaller; one much-cited study accounted only for the cross-section of the turbine towers for its land use estimate.
The true measure is probably somewhere in the middle, neither as dire as wind power detractors claim, but neither as negligible as the most optimistic assessments. But while such estimates are good for scoring political points, a real issue is determining the optimal number of turbines you can place onto a parcel of land. Build too few and the power density of the wind farm goes down; build too many and the turbines start interfering with one another, reducing efficiency.
In spite of the efforts made to improve wind turbine technology, the spacing of turbines is still more an art than a science. According to the National Renewable Energy Laboratory in Golden, Colo., spacing is based on the diameter of the area swept by the turbine blades, with the rule of thumb to space the turbines in arrays five diameters by ten diameters. Such a spacing is intended to allow for the turbines to draw as much energy from the wind as possible—up to the Betz limit of 59 percent—without interfering with other turbines situated downwind.
But wind tunnel experiments conducted at Johns Hopkins University in Baltimore suggest that the 5 x 10 spacing may be too close. The work, conducted by Johns Hopkins mechanical engineering professor Charles Meneveau and Johan Meyers of the Catholic University of Leuven in Belgium, placed an array of model turbines in a wind tunnel where the air flow was disturbed to provide a more natural turbulent flow. As the wind passed through the model turbines, high-resolution cameras imaged the air flow that contained puffs of smoke illuminated by strobing lasers.
Meneveau and Meyers found that the energy extracted from a wind turbine array is less a matter of wind passing through one turbine to the next and more of the turbulence created behind one turbine drawing down higher velocity wind from above. Because of this, the engineers believe that the turbines on existing wind farms are too close together to generate maximum power; instead, the turbines ought to be some 15 turbine blade diameters apart.
Another recent experiment, this one conducted in field conditions in California, came to the opposite conclusion—but with a twist. John Dabiri at the California Institute of Technology in Pasadena, found that vertical-axis turbines should be placed as close as four turbine diameters apart to extract the maximum power. That’s because unlike the standard propeller-style turbines, vertical-axis machines can use the vortices in the wind generated by upwind units, much the way that fish swimming in schools can use vortices created by their schoolmates.
Results from field tests over ten days in September showed that vertical-axis turbines spaced four diameters apart had power densities of 30 to 45 watts per square meter—between 10 and 15 times as great as standard wind farms. And the turbines tested were only 10 meters tall, just a fraction of the height of standard wind turbines.
Dabiri hopes that these results could lead to a reassessment of vertical-axis turbines which, if his results prove to scale up to industrial levels, could revolutionize the wind power sector.
BUILDER NAMED FOR TWO U.S. WIND PROJECTS
With two wind energy projects in the works, Western Wind Energy Corp., has hired a contractor to build both wind farms with a total nameplate capacity of 130 MW. The contractor, RMT Inc., will build a 120 MW wind farm called Windstar in Tehachapi, Calif., and a 10 MW project known as Kingman, in Mohave County, Ariz.
According to the companies, RMT will handle engineering, procurement, and construction of the civil and electrical balance of plant for both projects.
Western Wind Energy announced deals with Gamesa earlier to supply turbines. In December it ordered turbines with a total capacity of 120 MW for the Windstar project. In January, it ordered turbines for a total of 10 MW for Kingman.
RMT is a unit of Alliant Energy Corp. and is headquartered in Madison, Wis. Western Wind Energy is based in Vancouver, British Columbia.
Gamesa operates in a number of countries and has its headquarters in Zamudio, in the Vizcaya region of Spain.
DON'T FEAR THE DRILL
By Jean Thilmany
Can a gadget that cancels out the noise of the dental drill help usher in an age of lessened dental anxiety? Perhaps, according to a King’s College London researcher who pioneered the invention.
The prototype device works in much the same was as those noise-canceling headphones so popular for airplane use, though it’s specially designed to deal with the very high pitch of the dental drill.
Dental patients plug the device into their MP3 players or mobile phones, and then plug the headphones into the device, so they can listen to music while the unpleasant sound of the drill and suction equipment are completely blocked out, said Brian Miller, professor of blended learning at King’s College London’s dental institute, who created the noise-canceling device.
A patient can still hear the dentist or other members of the dental team speaking, but the gadget filters unwanted sounds like drilling, he said.
The device contains a microphone and a chip that analyzes the incoming sound wave. It produces an inverted wave to cancel unwanted noise. It also uses adaptive filtering technology, in which electronic filters lock onto sound waves and remove them, even when the drill’s amplitude and frequency change, Miller said.
Miller said he was inspired to create the device by Lotus Cars’ efforts to develop a system that removes unpleasant road noise, but still allows drivers to hear emergency sirens. He then spent more than a decade collaborating with engineering researchers at Brunel University of London and London South Bank University.
Although the product is not yet available to dental practitioners, Miller and his team are searching for an investor to help bring it to market.
“Many people put off going to the dentist because of anxiety associated with the noise of the dentist's drill,” Miller said. “This device has the potential to make fear of the drill a thing of the past.
“The beauty of this gadget is that it would be fairly cost-effective for dentists to buy, and any patient with an MP3 player would be able to benefit from it, at no extra cost,” he added.
STUDENT ROBOTICS COMPETITION AT DESIGN CONFERENCE
By Brian Trease
ASME will sponsor the Student Mechanism and Robot Design Competition in conjunction with the 2011 International Design Engineering Technical Conferences in Washington , D.C., this August. Deadline for submitting a letter of intent to participate is April 1.
This competition, which is open to graduate and undergraduate students, as teams or individuals, consists of two rounds. In the first round, competitors submit reports of their designs. Final written reports are due by May 2.
Judging of the reports determines the projects that will proceed to the second round. Finalists will be notified by June 17.
In round two, selected competitors are invited to present their designs during the conference, August 28-31, in Washington.
The competition is part of the 35th ASME Annual Mechanisms and Robotics Conference, which meets during the design engineering conferences. Winners of the competition will be recognized during the Mechanisms and Robotics luncheon at the conference, and will receive awards, which in the past have included both cash and software prizes.
For purposes of the competition, a mechanism is: “Any device that transmits a force or a motion to perform a mechanical task. It may consist of rigid or deformable bodies connected with kinematic or flexural joints. It may be constructed of any type of materials, including smart and other active materials. It may be actuated by means of any transduction principle and employ any form of energy input. The size of the device can range from the nano-scale to macro-scale.”
A robot is: “An electromechanical system which, by its appearance or movements, conveys a sense that it has intent or agency of its own. A robot should be able to do some or all of the following: move around, operate a mechanical linkage, sense and manipulate its environment, and exhibit intelligent behavior, such as behavior that mimics humans or other animals. The size of a robot can range from the nano-scale to macro-scale.”
The National Science Foundation has provided funding to support the travel costs of up to two participants from each design team that makes it to the final round. The funds will cover the ASME IDETC registration, hotel stay, air fare, and a per diem allowance for meals. Students from all U.S.-based institutions are eligible for this funding.
Details on how to participate can be found at the contest Web site, http://sites.google.com/site/asmesmrdc.
The author is coordinator for the Mechanisms—Undergraduate Division of the competition.
MODIFIED CHOPPERS FOR AIRLIFT MISSIONS
A transport services company has received two Sikorsky S-92 helicopters modified to carry cargo and passengers at the same time. It will use them in Afghanistan under a contract with the U.S. government.
They transport company, AAR Corp. based in Wood Dale, Ill., ordered the aircraft for a new contract, awarded last October, for airlift services in Afghanistan. The contract came from the U.S. Transport Command and has a one-year initial term with four one-year renewal options. The value of the contract could total approximately $450 million over the five-year term.
Two S-92 helicopters with modified interiors are entering airlift
service in Afghanistan.
Sikorsky Aircraft Corp. modified the interiors, which have been certified by the Federal Aviation Administration. They are reconfigurable and can accommodate seating for passengers and space for up to three cargo pallets measuring 4 feet in each dimension. The pallets can be secured to rings in the seat tracks and cabin walls to assure crashworthiness. Sikorsky also developed special fire containment cargo covers that will contain and suffocate flames. The containment covers include smoke detectors.
Sikorsky designed a fabric partition to separate passenger seating from the cargo space, and added a fire extinguisher and protective breathing equipment for passengers and crew.
AAR already operates 15 Sikorsky S-61N aircraft in various mission roles, including Afghanistan.
Sikorsky said it has delivered 129 S-92 helicopters since September 2004 to commercial customers. At the end of January this year, the worldwide S-92 fleet had accumulated 285,000 flight hours, more than any other commercial fleet of Sikorsky helicopters in the same period of time.
A military version of the S-92 airframe, the CH148 helicopter equipped for naval operations, is being designed and produced for the Canadian government. Sikorsky and Lockheed Martin have proposed a variant to the U.S. Navy for the next Marine One helicopter fleet, which transports the president of the
IN PURSUIT OF PIPELINES
In a bid to strengthen its position in the pipeline components business, EnPro Industries Inc., a manufacturer of seals, engines, and other industrial goods, has agreed to acquire the business of Pipeline Seal and Insulator Inc. and its affiliates. EnPro’s principal products include industrial gaskets and sealing systems, bearings, wheel-end components, sealing components reciprocating compressors, and diesel engines and dual-fuel engines.
PSI is a privately-owned group of companies that manufacture products used in oil, gas, water, and wastewater pipelines. Its products range from flange sealing and isolation products to a modular system for sealing pipeline penetrations into walls, floors, ceilings, and bulkheads. It has facilities in the United States, Germany, and the United Kingdom, and will operate as part of EnPro's Garlock group of companies, which make a variety of industrial sealing products.
The purchase price is $100 million and the deal is expected to close by the end of March, a spokesman said.
According to Steve Macadam, EnPro’s president and chief executive officer, the acquisition of PSI will strengthen the Garlock Group’s business with global oil and gas markets and with the water and wastewater markets, where substantial demand is expected to materialize with increasing infrastructure improvements in coming years.
EnPro is based in Charlotte, N.C. PSI employs about 200 people with primary manufacturing locations in Houston, Texas; St. Neots, U.K.; and Nehren and Furth, Germany. The company also has operations in Dubai and Malaysia.
The International Gas Turbine Institute has lined up three keynote speakers for the opening day of ASME Turbo Expo 2011, to be held June 6-10 in Vancouver, British Columbia. Walter DiBartolomeo, vice president of engineering at Pratt & Whitney Canada; Roland Fischer, chief executive officer, business unit products, fossil power generation, Siemens Energy, and Gary Mercer, senior executive of engineering at GE Energy, will discuss “Clean and Efficient Turbomachinery Technologies for Future Low Carbon Economies” at the Vancouver Exhibition and Conference Centre. /// The National Institute of Standards and Technology has discontinued calibration services for mercury thermometers, as part of a larger effort in collaboration with government agencies and private organizations to phase out the use of mercury thermometers and reduce the amount of mercury in the environment. /// Creative Dimension Software Ltd. of Guildford, England, has released 3DSOM Pro version 3, a tool that creates 3-D models from photographs. It allows users to build concave models of objects including vases, bowls, and complex objects that are hard to model. /// A maker of 3-D modeling software, Ashlar-Vellum of Austin, Texas, is now shipping service pack 3 for Graphite version 8, software for 2-D and 3-D wireframe drafting. /// EMCOR Group Inc., based in Norwalk, Conn., has acquired Bahnson Holdings Inc., a privately held mechanical construction services company headquartered in Winston-Salem, N.C. Terms of the transaction were not disclosed.