AEDC's LDV technology pioneers meet the future

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  A recent gathering at AEDC's laser technology laboratory brought five of the center's pioneers on laser Doppler velocimetry together with Dr. Todd Lowe, whose company's subminiature three-component laser Doppler velocimeter (SM3 LDV) had undergone acceptance testing there.

"The people we were meeting with are pioneers, not only [with] flow measurements, but instrumentation in general," said Dr. Lowe, vice president of and lead investigator with Applied University Research, Inc., located in Blacksburg, Va. "They solved initially difficult problems using technology that was just coming along and it's an inspiration for me to be here hosting them."

ATA's Fred Heltsley, an engineering specialist in applied technology, said, "The SM3 LDV represents the very latest in laser Doppler velocimeter (LDV) flow diagnostics hardware and was developed under a Small Business Innovation Research (SBIR) program for use in AEDC's Tunnel 16T."

The fact that this system is capable of measuring three components of velocity sets it apart from most other LDV systems at this scale, according to Dr. Lowe.

Dr. Lowe said his team's success in developing their hardware is due in large part to the pioneering work done in the past by those he met in the lab.

"There were folks here who are aerodynamicists, computer scientists, programmers and electrical engineers," he said. "It really shows it's a multidisciplinary [effort] to get instrumentation, specifically laser instrumentation in this case, to work. It meant a lot to see these folks here and to know that they worked so closely together with all these different backgrounds and have success."

Dr. Lowe said it is clear that the group's expertise preceded and went beyond their laser-related work.

"I am certain that these folks have experience using other types of instrumentation," he said. "This could be probes such as hot wire anemometers [and] pressure probes in the wind tunnels. Then, as laser diagnostics came along, that really changed the game in the way that we measure flows."

AEDC's personnel became involved at the beginning of LDV technology development more than 50 years ago, according to Heltsley.

"AEDC holds U.S. patents for both the first and second generation LDV data acquisition/processing systems," he said. "Counter processor technology, the first patent, was the industry standard for LDV for many years, as was the more recent Fourier transform processor technology. A modified version of Fourier transform processing continues to be the LDV standard in industry."

Heltsley added, "The former AEDC employees included optical and electronics designers, instrument technicians, software developers, system operators and data analysts who have been involved in the AEDC LDV system development over the past decades.

"The primary electronic designer and holder of both of the aforementioned patents, Henry Kalb, is currently living and growing his roses in Florida. Another prime contributor, Les Crossway, has only recently passed away."

Dr. Lowe said he was aware of AEDC's contributions to LDV technology prior to the recent get together.

"I did not know all of the folks involved, but [had been] following some of the old literature," he said. "I've always been excited to see what's been done before."

Dr. Lowe said he owes much of the success for the recent SM3 LDV development to both the pioneering work done by AEDC's pioneers and people like Heltsley.

"Fred Heltsley has been involved with this [the SM3 LDV development] project from the beginning and seen that here's something that 16T (AEDC's 16-foot transonic wind tunnel) can really use."

Dr. Lowe said reading the literature that included work done by AEDC's pioneers established the foundation that led to the current technology.

"This link is so important because I'd be making a ton of mistakes if I didn't use [the] experience of these pioneers in the field to push things forward," he said. "I've done my homework. You absolutely have to - you don't want to repeat anybody's mistakes, you don't want to make them again and you need to be doing things the best way possible."

Donald Brayton, an electrical engineer who retired from AEDC in 1995, enjoyed seeing old friends, meeting Dr. Lowe and seeing the latest laser diagnostics technology.

"Well, I had a personal patent or two on self-aligning optics which made setting up a system very simple," recalled Brayton, who first came to AEDC in 1965. "I also came up with a dual scatter principle that increased the efficiency of the systems as far as collecting radiation goes and getting a strong signal."

Brayton said he and many of his colleagues spent the first 12 years working toward the development of an LDV system. The first one was based on an early reference beam system NASA had developed.

"We were in an experimental research group, just trying to get that technology working here at the center," he said. "Then we put an active system in the one-foot transonic tunnel 1T here at the base. Virgil Cline was the project engineer on the first one-foot tunnel application. We also put an active system in the four-foot transonic wind tunnel 4T here to measure the free stream velocity. Les Crossway was the project engineer for that experiment."

Brayton said an improved LDV system installed in the supersonic Tunnel A proved to be more useful than originally anticipated.

"It turned out the Tunnel A application was more than a free stream experiment, with the possibility of looking at flow around a model in the tunnel," he said. "Our system there was forward scatter. The original systems in tunnel 1T were all back scatter, which have a much weaker signal. During the early 1T experiments no particulates were injected into the tunnel for scattering light and measuring their velocity, just natural particles that are in the air. We were able to measure boundary layers around the Tunnel A model by injecting sub-micron sized particles into the flow.

He said that later they did a lot of successful model flow and boundary layer work in both 1T and Tunnel A, mainly with forward scattered light and injected particles. The forward scatter light is very intense, compared to backscatter light.

Brayton was impressed by what he saw during his visit to the laser lab.

"The component technologies of the SM3 LDV are so advanced compared to where we were," he said. "We used water cells, now they're using solid material Bragg Cell models. It's really amazing the point that technology has progressed."

For Dr. Lowe, meeting these AEDC pioneers was the highpoint of the visit.

"This was a major honor, and you can probably tell it in my voice, how excited I am," he said.