ARNOLD AIR FORCE BASE, Tenn. -- After a compressor in their facility went down, personnel at Arnold Engineering Development Complex Hypervelocity Wind Tunnel 9 in White Oak, Maryland, moved swiftly to install a system capable of picking up the slack.
From the initial conceptualization to the finalization of operating procedures, the Tunnel 9 team completed all of the steps necessary to integrate the new Containerized Vacuum System into the site over a 10-month period in 2019.
The primary purpose of the Containerized Vacuum System, or CVS, is to reduce the pressure in the 200,000 cubic foot Tunnel 9 Vacuum Sphere, which acts as a low-pressure reservoir for pressurized nitrogen propelled through the nozzle and test chamber. By using the CVS, the pressure in the vacuum sphere is reduced to levels at which test operations can be performed. The CVS can be operated both independently and in conjunction with the remaining functional compressors.
The award-winning team project that brought the CVS to fruition was executed in parallel to the vacuum compressor repair effort.
The compressor that required repair is one of four vacuum compressors located within the Tunnel 9 Vacuum Compressor Plant, a four-stage plant used by Tunnel 9 to generate the low backpressure required to test at extreme speeds and conditions. The events that led to this unit being taken out of commission began in mid-October 2018 when bearing vibration levels reached alarm levels and the compressor was idled.
From that point through the end of 2018, inspections were conducted and adjustments were made in an effort to address the vibrations and return the compressor to operation status as quickly as possible. This included sending the compressor rotor to the Model and Machine Shop at Arnold Air Force Base, the AEDC headquarters, for repair. Vibrations levels, however, continued to exceed limits and the compressor rotor was sent to technicians with a company that specializes in rotating machinery to be balanced.
Upon the return of the rotor in late January 2019, the compressor was in operation again. Vibration levels, although reduced, still exceeded the limits. Test operations were halted in February 2019 until a root cause of the vibration issues could be determined.
Prior to this, Tunnel 9 personnel had begun exploring other solutions that would enable test operations to resume. In January 2019, they investigated the possibility of renting a compressor and also began working with vendors to identify an alternate solution. These vendors included Cummins-Wagner, a company that had provided other subsystems to Tunnel 9 in the past. They suggested the use of a large vacuum pump system integrated into a shipping container that could be delivered as a “plug and play” solution.
The Tunnel 9 team also contacted members of the Air Force Research Laboratory team working in Tunnel D at Arnold AFB, who provided quotes from other similar vendors. Following discussions with the vendors, it was concluded that the direct replacement of the compressor was not feasible with a vacuum pump system.
“Perfect had become the enemy of good enough,” said Tunnel 9 Technical Director John Lafferty. “We needed backup capability and had initially held the capabilities of the four-stage Vacuum Compressor Plant up as the standard. A good enough system that provided some capability was needed to maintain operability. It may be slower, but one run a day is infinitely better than no runs a day.”
The Tunnel 9 team then began developing requirements for a standalone system. This alternative vacuum source - the CVS - would need to be located in an area where it could be easily connected to existing vacuum piping and electrical infrastructure while contained in its own housing, as there was no room in the Vacuum Compressor Plant for new vacuum pumps. The system would also need to be capable of being used in conjunction with the existing Vacuum Compressor Plant and, if used alone, capable of reducing the pressure in the vacuum sphere to a level to meet testing conditions in a short enough time to allow at least one run per day.
“In the event that we could not get the vacuum compressor repaired in a timely manner, the CVS was intended to allow Tunnel 9 to resume test operations at the expense of operational efficiency,” said Nicholas Fredrick, Tunnel 9 Chief Facility Engineer.
Following this initial conceptualization of the system, the CVS Procurement and Installation statement of work was submitted to AEDC Contracting in early March 2019.
Service Life Extension Program, or SLEP, money was identified as a funding source for the CVS.
Site preparation for the system began at Tunnel 9 in June 2019. Later that month, the fourth compressor was returned to operational status. However, this did not last as the compressor developed new vibration problems in mid-October 2019 and had to again be taken offline.
The CVS containers were delivered in late September and the system was installed. Following the loss of the compressor, efforts immediately pivoted to expedite completion of this project. An initial commissioning test was completed in late October, and procedures for hybrid CVS and Vacuum Compressor Plant operations were finalized in November.
The CVS was able to achieve the redundancy needed to fill in for the downed compressor and minimize facility downtime. The three existing compressors are used to reduce sphere pressure, at which point the CVS can be brought online to complete the process of achieving the desired pressure. Three tunnel runs per day are possible with the three compressors and the CVS operated in synchrony.
One tunnel run per day is possible if operations are conducted solely with the CVS. Fredrick said the possibility of increasing this number will require further efforts.
“The CVS reduces the pressure in the vacuum sphere at a much lower rate than the Vacuum Compressor Plant,” he said. “With our currently-approved procedures and hazard analyses, we can achieve one run a day without overtime using solely the CVS to reduce the pressure in the sphere. We believe that there is a path forward that will improve the operational efficiency of the CVS that will allow us to achieve two or three runs per day using solely the CVS, but this will require revisions to existing procedures and hazard analyses, as well as new procedures. We are currently attempting to implement these changes but have not yet validated that we can achieve two or three runs per day using only the CVS.”
The Vacuum Compressor Plant will soon be taken offline for approximately three months for a planned maintenance. During that time, the CVS will serve as the sole vacuum source and will allow for the continuation of test operations during the maintenance outage.
“The CVS can operate independently of the Vacuum Compressor Plant,” Fredrick said. “This will allow Tunnel 9 to continue test operations during a time of increased customer demand and still proceed with much-needed maintenance activities in the Vacuum Compressor Plant.”
During this outage, Tunnel 9 personnel are planning to perform the Initial Operational Capability Calibration Test for the Mach 18 capability using the CVS.
“This project was completed just in time and has allowed us to maintain operability during this historic increase in hypersonic ground testing,” Lafferty said. “The Vacuum Compressor Plant is 1930s and 40s vintage hardware and technology, requiring significant SLEP maintenance to keep it operational. We have already reaped the benefit of this investment, and it has helped us look at other parts of our operation to determine where we might do things differently to improve our operational efficiency in the future.
“It was an amazing team effort.”
Those involved with the CVS were recently recognized. In February, the Tunnel 9 team, along with AEDC team members in Contracting and Financial Management and Dr. Jerrod Hofferth with AFRL, received an AEDC Annual Award for Technical Achievement for their work on the project.
“The success of this project was a result of the tremendous effort put forth by the entire team,” Fredrick said. “This includes the Tunnel 9 System Engineers and Engineering Technicians, the Air Force Project Managers, the safety team, the contracting officers, Huang-Gaghan personnel, Airtech/Cummins-Wagner, and everyone else who provided support.
“I’m proud to have been a small part of it and am glad that it turned out as well as it did.”