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Blast from the Past PUBLIC ACCESS

Building a New Jet Engine test Facitlity to Replicate Decades-old Capabilities.

[+] Author Notes

William Loob is a freelance writer based in New York.

Mechanical Engineering 121(08), 64-66 (Aug 01, 1999) (3 pages) doi:10.1115/1.1999-AUG-6

This article presents a review about the jet engine testing facilities of the Naval Air Warfare Center Aircraft Division in Trenton, NJ, that had to be moved to a base run by another branch of the military, the Arnold Engineering Development Center at Arnold Air Force Base in Tennessee. The jet engine testing complex at Trenton had been built in the 1950s. The restriction effectively ruled out any upgrades so long as the Navy’s engine test requirements could be met by replicating the capabilities of the old facility. The natural tendency of the engineers and planners looking at the project was to think immediately about how the facility could be improved with modern designs. For the restriction on not improving the test capability at Trenton, the project ironically provided an expansion of services. This is built to subject the Navy engines to definite environmental conditions, and as long as the Navy has that kind of test requirement. It is a capability that is available not only to the Navy and Air Force, but to the Army, Marines, and private industry as well.

SAVING TAXPAYERS MONEY is a hot issue in American politics, and it often drives Congress to write specific provisions into new laws that are designed to curtail government spending. The federal Base Realignment and Closure Act was intended to save taxpayers n1.oney by systematically closing military bases that are deemed unnecessary. Unfortunately, the reality of military operations rarely provides clear-cut situations in which all of the functions supported by a single base can be considered superfluous. In deciding to close any base, one usually finds that certain functions have to be shifted to another base somewhere else.

To maintain such essential capabiliti es, Congress mandated that the Department of De fen se take specific measures to transfer to new locations the relevant functions and facilities of a base facing closure. So when the time came to close the US. Navy station in Trenton, NJ, the jet engine testing facilities of the Naval Air Warfare Center Aircraft Division that had been housed on the site had to be moved to a base run by another branch of the military, the Arnold Engineering D evelopment Center at Arnold Air Force Base in Tennessee.

Moving the capabilities of a large testing laboratory to another site is always a major undertaking. But, ironically, one of the biggest problems encountered by the designers and engineers of the new facility at Arnold Center was psycholo gical rather than technical.

"The BRAC law said that the Navy was responsible for moving a similar type of capability from one location to the other, which meant that no improvements could be made," said John K. Lominac, an engineer who managed the Trenton Transition Project.

The idea behind that provision in the law was to limit spending .on the actual transfer of capabilities from one site to another, Lominac explained. The jet engine testing complex at Trenton had been built in the 1950s. The restriction effectively ruled out any upgrades so long as the Navy's engine test requirements could be met by replicating the capabilities of the old facility. The natural tendency of the engineers and planners looking at the project was to think immediately about how the facility could be improved with modern designs.

Thus, the first hurdle was getting the project engineers to break their accustomed ways of thinking-that is, not to think of ways to improve design, but merely to reproduce the capabilities of a facility as faithfully as possible. "That was the biggest handcuff that we fought in the beginning," Lominac said.

Once the design goals were clearly established and communicated to the project team, the problem-solving sessions began. The Navy had different test requirements for its jet engines than were in the regular arsenal of tests for the Air Force faci lity, which meant that facilities at Arnold had to expand the menu of tests to accommodate the N avy's requirements.

Two test cells at the Trenton base were used for conducting environmental tes ts on turbine engines of the size used in fighter aircraft. T he test cells-fundamentally stru ctures built in three sections for air intake, engine test compartment, and exh aust stack-were equipped with ram air inlets and could simulate a variety of sea level environmental conditions, which provided tests for salt-air corrosion and j et ingestion of water, ice, or sand.

"These are tests that the Air Force did not do because we don 't have that requirement for salt spray or sand spray ingestion into the engine," Lominac said. "That was a new way of doing business for us."

Most of the hardware, su ch as measurement equipment, display systems, and piping system components, could simply be transported to the new site. However, the test cells themselves and the control and data processing rooms were integral parts of the building structure and could not be moved. To provide the required testing capability at Arnold, new test cells had to be constru cted.

The overall challenge for Lominac and his project team was to create test cells at Arnold that would perform the kinds of tests that the Navy required and also keep down costs, as mandated by the law. According to Lominac,

"We had to answer, 'What can we find that will mirror the configuration in th e most economical manner?'" A good substitu te test cell in the Air Force inventory, and a good bit of luck, provided that answer. "We were fortunate that, as part of the BRAC '93 action, two Air Force bases had these T-9 test cells that were going to be surp].u sed," Lominac recalled . U nlike the test cells at Trenton, the A/ F32T -9 N oise Suppression System test cells were designed as transportable stru ctures that could be broken down and transferred to Arnold. Major modifications were still needed to replicate some of the functions required fo r specific tests, but the T-9 test cells formed the foundation for the new facility.

"We liked the size, shape, and configuration of the test cell, but by virtue of the N avy's requirements, modifications had to be made," Lominac said. The architecture and engineering firm Burns & McDonnell in Kansas City, Mo., was chosen to design the necessary structural modifications, and the firm worked on the construction site under supervision of the Army Corps of Engineers. Once the designs were approved, the two test cells- one from North Dakota and the other fi'om a base in New York-were disassembled and sent to the original manufacturer, Vital Link Inc. in Sealy, Texas, to make the modifications.

Most of the modifica tions to the test cells involved adding capability to accommodate ram air testing, which involves directing forced, conditioned air from compresso rs to be fed to the engine intake thro ugh a du ct. Conditioning both temperature and pressure of the air that the engine breathes simulates a variety of operating conditions. The T-9 test cells were not designed to accommodate a ram air duct, and so needed a major structural modification.

To determine the feasibility of the proposed modifications, however, a scale model study needed to be approved. "This is not normal, where we would physically construct a scale model replica of a facility," Lominac said. One area of uncertainty was how the airflow would be affected by the shape of the ram air duct. "It was a smart thing for us to do," he said. "When we came up with this concept, we were concerned about how the structural modifications would work, so the Navy authorized and funded a scale model test to see."

Artist's rendering of the plan for the A/F32T-9NSS test cell: Sections from left are the primary air intake, engine test section, exhaust gas augmentor, and exhaust stack.

The bell mouth of an engine is covered with a wire mesh to prevent foreign object debris from entering the turbine during testing.

Grahic Jump LocationThe bell mouth of an engine is covered with a wire mesh to prevent foreign object debris from entering the turbine during testing.

To build a working 1 I 12-scale model, project leaders ended up talking to ITF Services of Cincinnati. The firm had experience in constructing working scale models for companies that used the models to study engineering hypotheses. It showed that ITF could work well with the aeronautical engineers who were modeling the airflow in the modified system, Lominac said. Once the scale model was built, the airflow studies were conducted using an FII0 engine simulator at the Ohio State University Aeronautical and Astronautical Research Laboratory in Columbus.

A simulator stood in for a real engine during the initial trial runs of a test cell at the Arnold Engineering Development Center at Arnold Air Force Base, Tenn.

Grahic Jump LocationA simulator stood in for a real engine during the initial trial runs of a test cell at the Arnold Engineering Development Center at Arnold Air Force Base, Tenn.

"We simulated flow in the scale model using a smoke generator to look at the turbulence in cells and it turned out that fine-tuning was needed," Lominac said. The T-9 test cells were not originally designed specifically to provide a smooth airflow into the test chamber, a feature that was needed for some of the Navy's test purposes. Analysis of the scale-model test data revealed that additional modifications were needed to reduce the front cell velocity distortion in the modified T-9s. In their original configuration, the T-9 test cells had more than twice the distortion than that measured at the Trenton facility. The scale-model studies demonstrated that two flow-smoothing screens, installed before and after the primary acoustic baffies, would reduce the velocity distortion to levels comparable with the test cells at Trenton.

The scale model study also verified that a known problem with the exhaust system of the T-9 test cell would pose an even greater maintenance problem when conducting environmental tests in a modified version of the cell. High levels of low-frequency vibration inherent in the T-9 can cause physical damage to the control room and equipment adjacent to the test cell.

Problems with the vibrations in the exhaust system are related mostly to "the vibration and harmonics established running an engine in afterburner mode," Lominac said. "We always have to be cognizant of what the structure is doing when we run these tests ." The problem was addressed by enclosing the augmentor tube leading to the exhaust stack in concrete and modifYing the tube itself.

In all, the transition of jet engine test capabilities from Trenton took five years to complete. The total cost of nearly $9 million could well be far less than it might have cost without the restrictions set by law. The new facilities at Arnold, now complete and fully operational, have added a new bank of test options to those conducted by the Air Force.

For the restriction on not improving the test capability at Trenton, the project ironically still provided an expansion of services, Lominac said. "This is built to subject the Navy engines to definite environmental conditions, and as long as the Navy has that kind of test requirement, we can provide the capability." And it is a capability that is available not only to the Navy and Air Force, but to the Army, Marines, and private industry as well.

Copyright © 1999 by ASME
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