AEDC engineer’s energy reduction plan to save the test customer 6 percent

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  When Mike Mills, an ATA Propulsion Wind Tunnel Facility performance engineer, shared his plan for reducing power consumption in the facility's 16-foot transonic tunnel (16T), ATA General Manager Steven Pearson wanted to learn more.

Mills said communicating the idea, first to ATA's leadership and then to a test team at 16T was critical to getting buy-in from all those involved to give the plan a try.

"There's a whole host of folks who are involved with the tunnel operation, who you work with," he said. "You work with the project, test and plant engineers who operate the facility and prepare an agreement.

"You think through the safety issues [to] make sure there's no risk you're adding. We went through that whole process with the folks who operate the facility before we went out there and tried this."

Mills added, "The project engineers' staff estimated they would reduce the cost of this test by $26,000. It was a win-win for everybody. AEDC will use less energy, which is one of our big goals and it's a big emphasis of the commander and the customer saved a little money."

Mills had conducted testing in PWT's 16T and 16-foot supersonic wind tunnel (16S) early in his career at AEDC, which began in 1978.

"My primary job over the years has been to conduct the [air] flow calibrations of 16T, 16S and 4T (4-foot transonic wind tunnel) and now that's actually taking in von Kármán Gas Dynamics Facility (VKF) Wind Tunnels A, B and C," he said. "When I say calibrate it's when we put probes in the test section.

"We measure the flow speed and the quality and uniformity and the angularity of the flow. I've calibrated 16T, 16S, 4T and Tunnels B and C in VKF, the only one I haven't is Tunnel A. And that's coming up soon."

Mills has also worked in other test facilities at AEDC over the years.

"I worked in the P plant for several years back in the late 1980s or early 1990s and learned a lot about how the facilities operate and all the equipment that drives the flow in the tunnels," he recalls. "I've always done the same thing, calibration and studies to improve the flow and feasibility studies to increase performance or capability."

His current project on 16T began in 2010, when the interest in reducing energy consumption at AEDC started gaining traction.

"Steve Pearson, ATA's general manager, had some money to do some studies of how we might reduce energy in 16T," Mills said. "We made a pitch to him for some ideas that we would like to try. We had already begun looking at energy reduction using funds provided by Lt. Col. Davis and Jack Walters in the Air Force TSTW (Propulsion Wind Tunnel Ground Test Complex) office. The funds provided by Steve Pearson allowed us to expand this work and prove the ideas in the tunnel."

The idea that showed the most promise involved reducing the tunnel pressure ratio. A recent store separation test being conducted in 16T provided an opportunity to assess this approach, Mills said.

"We discussed this idea with the customer and proposed that he pay for a short run in the tunnel with the potential of reducing the cost of his test," he said. "Once the test customer agreed, Dave Anderson, ATA's Captive Trajectory System (CTS) project engineer, integrated the proposed runs into the day's test plan.

"He [the customer] did a few runs to demonstrate that reducing the pressure ratio in the tunnel would not affect the data."

Mills said his goal was to achieve energy reduction without sacrificing the quality of the test data.

"We were able to reduce the power for this test by 3 megawatts," Mills said. "We were running about 50 megawatts on the main motor drive, and were able to reduce that by about 6 percent."

A large compressor, approximately 30 feet in diameter, drives the airflow around the inside of 16T.

"The compressor provides a rise in pressure to push air around the circuit," he said. "There are losses around the circuit caused by friction and different elements in the circuit. We're talking about the overall pressure ratio, which is the ratio of the stagnation pressure as measured at the front and rear of the compressor in the wind tunnel."

He said this translates to the ratio of the highest and lowest pressures in the circuit or tunnel.

"We have some flexibility on the ratio we can run," he said. "We've been setting it conservatively over the years. The idea was to see if we could reduce some of that conservatism, eat into that margin a little bit, because the emphasis is on energy reduction."

The escalating cost of electricity prompted Mills to consider the current effort.

He said the recent project to reduce energy demands at 16T is addressing challenges that he and other engineers have been dealing with for years, including measuring airflow pressure losses in the wind tunnel.

"This has been done in the past, this isn't a new idea," Mills said. "16T's energy has always been an issue, from day one. There are lots of reports - lots of studies have been done over the last 56 years. But we'd like to look at it in more detail, since there's a renewed interest in energy reduction."

Mills said more can be done to save energy, which is worthwhile, but he also cautioned against over-stating the expectations.

"We need to focus on other things we can do in the circuit of 16T," he said. "Those solutions may apply to other tunnels, to reduce those losses, because the power it takes to drive that compressor is directly affected by the rise in pressure provided by the compressor.

"This rise in pressure required is simply the inverse of the losses around the circuit and the compressor is making up the losses. If we can reduce the losses, we can reduce the power. If the rise required by the compressor is lowered, then we can reduce the energy consumption."

Mills said the recent project was simple to implement and test.

"The angle of the stator or stationary compressor blades can be changed at the computer console in the control room," he said.

Mills said making the pressure ratio change while continuing the test and comparing the data under the changed conditions took approximately 20 minutes.

Pete Macaluso was AEDC's Air Force primary project manager on the test used for the recent energy reduction effort.

"Mike [Mills] contacted me with his proposal for investigation," Macaluso said. "He and I discussed the data gathering options with the customer and the expected cost and potential future cost savings. Mike, Craig and I then participated in the data gathering during the test. Finally, Mike and Craig verified the power reduction savings, and I estimated the cost savings impact to the customer's test.

"Based on my estimates from the point in time of the investigation to the end of the test, my customer realized a cost savings of approximately $31,000. The technique used to reduce power costs is now implemented for all future tests that use the Captive Trajectory System (CTS)."

Macaluso said it is important to put the benefits of the method into perspective.

"The individual cost savings to each future test is dependent on the specific test conditions and customer matrix," he said.

Mills believes the methods for saving energy and reducing test costs, although these provide an ongoing challenge, are clearly worthwhile, especially to the taxpayer.

"The whole emphasis on reducing the energy burden on the infrastructure at AEDC, on TVA and the country may involve lots of small steps, but they do add up and that's what we're doing," Mills said.