National Aeronautics and Space Administration

Glenn Research Center

Combustion Air Flow
PSL exterior showing air flow system
Air Flow System

Although not a wind tunnel, PSL could create high-speed airflow through the interior of the engine. Large compressors pushed the air through the system, heating or refrigerating equipment was used to heat or cool the air to the desired temperature, and air dryers were used remove moisture from the air. The system was linked to the lab’s central air system, which allowed it to augment the compressors in other test facilities.

Compressed Air System
Front of Access Building with Inlet Pipes
Airflow Inlet Pipes

Air flow was generated by large Elliott Company air compressors in the Equipment Building to simulate the speeds and altitude of flight. The compressors forced the air rapidly through the pipes towards the test section. After passing through temperature adjusting equipment, it was pumped through a pipe to the Shop and Access Building. The pipe split and wrapped around both sides of the building before entering it from the front on the second floor level. The air then entered the north end of one of the two test chambers. It passed through the chamber’s air-straightening vanes, then a bellmouth cowl in the bulkhead, and finally through the test section and the engine.

Over the years the air compression system was continually being upgraded and modified. In 1956 there were three 16,500 horsepower centrifugal compressors capable of delivering 112 pounds of air per second at 45 psig for a total 336 pounds of air. Each of these possessed three wheels in each of their three casings: two casings in the first stage and one in the second stage. A separate booster compressor could provide 183 pounds of air per second at 150 psig. Pressure-regulating valves in the test chambers kept the air supply at the desired range.

Combustion Flow
Air System Footage
Control Room
Control Room
Air Temperature Control
Air dryer tank
Air Dryer Tank

Depending on the type of test being run, the air flow into the engine would have to be either heated or refrigerated. Ramjets and engines, which would be operated at supersonic speeds, would need to be tested in hot conditions to simulate the heat generated by their velocity. Jet engines traveling at subsonic speeds would need to be tested in cold conditions to simulate the high-altitude air temperature.

The combustion air heaters located on the exterior of the Equipment Building were used to create the high temperatures. Ambient air was taken into the heaters and passed through vertical tubes that had been heated by a natural gas flame. PSL No. 1 and 2 contained three gas-powered heaters. Each heater would heat 125 pounds of air per second from 40 °F. Later a pebble bed heater was added to a test chamber to create extremely high temperatures found at hypersonic speeds.

Air heater
Air Heater

The refrigeration system for the high-altitude testing was not in the original PSL construction, but added soon afterwards. Temperatures found at 50,000 feet at speeds of Mach 0.6 to 1.5 could be recreated without the refrigeration equipment, but slower speeds required colder conditions. The refrigerated air was generated with expansion turbines located in the Equipment Building. Up to 112 pounds of air per second could be cooled by 100 °F as it passed through an expansion turbine.

The air at high altitudes was very dry, so the air flow had to be dehydrated before entering the test section. There were two dehydrator units that could reduce the moisture of 125 pounds of air per second 100,000 cubic feet of air per hour at temperatures between 40 and 600 °F. The air flowed up through a vertical tank and cascade trays with the liquid cooling medium. The air could be dried to 1 grain of moisture per pound as it passed through the dryer. The dryer contained 190,000 pounds of activated alumina.

Heater Footage
Dryer Controls
Dryer Controls
Air Heaters
Air Heaters