AEDC team provides Pratt & Whitney with cutting-edge turbine engine diagnostic tools

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  A specialized engineering technology team from Arnold Engineering Development Center provided critical support on an advanced diagnostics program and a recent successful F119 engine test at Pratt and Whitney's West Palm Beach engine test facility. 

Dr. Jeffery Lovett, the lead for Pratt & Whitney's Exhaust System Technology group expressed his appreciation for the "excellent support provided by AEDC and Aerospace Testing Alliance on our advanced augmentor diagnostics probe program over the past couple of years, which culminated in a very successful engine test." 

The comments were included in a letter of appreciation to the 717th Test Squadron Technical Director Dr. Charles Vining. Dr. Lovett also credited ATA engineers Gregg Beitel and David Plemmons for their role in working with the company's team in developing and fabricating the traversing rake probe system. He also recognized ATA Combustion Engineer Kent Wilcher for his role in developing and executing the engine tests. 

Don Gardner, ATA's lead engineer on the team, said it's important to understand why diagnostic probes are needed in ongoing augmentor work. 

An augmentor, also known as an afterburner, is a component added to some supersonic military aircraft engines to provide a temporary increase in thrust, both for supersonic flight and for takeoff. 

"There are rules and tools for doing augmentor light off, development and design work that were developed back in the 1950s and 1960s," he said. "Things have changed so much in terms of turbine engine exit conditions with the spacing, the augmentors themselves and the operating temperatures. Those things have changed so much that those rules don't apply very well any more. 

"The new high performance engines are driving this to a point where there is much less oxygen available, the speeds are faster, which results in light-off problems and a lot of engine instability issues." 

Beitel said the challenges to augmentor design and operation are more complicated than some engineers realize. 

"Even the exhaust of these turbine engines drive how that augmentor operates because you've got this turbulent, moderate temperature flow stream coming out of the engine core," he explained. "Now all of a sudden you want to stick this pipe on it and dump fuel in it to get short periods of augmented-plus power for high performance. 

Those working on these engines during the development process don't necessarily know what the exit conditions are from the turbine core to be able to adequately design the augmentor. And then when it's fielded they find these combustion instabilities due to turbulence and the way the fuel flow system works, creating headaches with combustion stability problems and screech and rumble issues." 

Beitel continued, "In an attempt to try to solve some of these issues they have with augmentors, it makes sense that the more measurements you have on these components during its operating envelope the better. More measurements will help them to try to solve some of those issues, particularly with combustion instability and light off. 

"Those are two huge problems that they would like to resolve. A lot of that occurs inside the augmentor around the flame holder which is actually just downstream of the turbine exit - sometimes, eight feet away from the nozzle exit, and it's up inside the engine. So, you have to actually get measurements down inside the engine. So, as a result, the traversing strut concept was first proposed by P&W and AFRL." 

This proposal provided AEDC with a window of opportunity. 

"The requirement to make measurements up inside the engine gave us a unique opportunity to work with the engine manufacturer to develop hardware, diagnostics systems that actually work configured to go inside the engine," Gardner said. "So, the engine manufacturer knew what this hardware was going to look like and could work with their designers to modify the engine casing and the liner (internal)." 

The traversing rake probe designed by the AEDC/P&W team was inserted inside the engine, something aircraft companies are often reluctant to do. 

"To me this collaborative effort was really amazing," said Kent Wilcher. "We were able to make measurements directly in the flow field environment. The probe extracts gas samples to measure products of combustion and fuel and with that data we try to calculate fuel-to-air ratios. This allowed us to make these measurements and improve the rules and tools for augmentor development in the future and allow P&W to set engine schedules and things based on real data instead of some rig data plus some models."