The Advanced Noise Control Fan shown here is located in NASA Glenn’s Aero-Acoustic Propulsion Laboratory. The 4-foot diameter fan is used to evaluate innovate aircraft engine noise reduction concepts less expensively and more quickly.

Aero-Acoustic Propulsion Laboratory (AAPL). NASA Glenn finished construction of the the Aero-Acoustic Propulsion Facility, a world-class noise-reduction research lab, in 1991.

Modern jet engines are loud, but they used to be much louder. NASA’s Glenn Research Center has been at the forefront of the nation’s efforts to reduce aircraft engine noise for over 70 years. During this time, the center has built an array of test facilities to carry out this work, culminating in the Aero-Acoustic Propulsion Laboratory (AAPL), a world-class noise-reduction research facility. The AAPL, referred to as “the dome,” contains multiple test rigs enclosed in a large, echo-free chamber. The unique 130-foot diameter and 65-foot-high hemispherical structure stands out on Glenn’s campus. Its triangular sections make it appear like a golf ball rising from the ground. The interior is covered in spiky, fiberglass sound-dampening wedges and an overhead array of microphones that capture engine noise data.

The black circle inside the helmet on the right contains some of the new elements of a noise reduction headphone that is part of an Active Noise Reduction system. It helps pilots hear better and improve communication during flight research missions.

Ultra High Bypass Ratio Turbofan model in the 9-by 15-Foot Low Speed Wind Tunnel

Aero-Acoustic Propulsion Laboratory (AAPL)

Pratt and Whitney J57 with a Greatex Nozzle in the Altitude Wind Tunnel

A Pratt and Whitney J57 engine is tested with a Greatex No.1 nozzle in the Altitude Wind Tunnel at the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. At the time the aircraft industry was preparing to introduce jet airliners to the nation’s airways. The noise produced by the large jet engines, however, posed a considerable problem for communities near airports. The NACA had formed a Special Subcommittee on Aircraft Noise to coordinate research on the issue. Preliminary tests showed that the source of the loudest noise was not the engine itself, but the mixing of the engine’s exhaust with the surrounding air in the atmosphere. The pressures resulting from this turbulence produced sound waves. Lewis researchers undertook a variety of noise-reduction studies involving engine design, throttling procedures, and noise suppressors. One of their first efforts focused on new types of nozzles to mix the exhaust with the surrounding air. The nozzles had a variety of shapes designed to slow down exhaust velocity before it combined with the air and thus decrease the noise. From January to May 1957 a Pratt and Whitney J57 engine was equipped with various shaped nozzles, as seen in this photograph, and run in simulated flight conditions in the Altitude Wind Tunnel. A number of nozzle configurations, including several multi-exit “organ pipe” designs, were created. It was found that the various nozzle types did reduce the noise levels, but they also reduced the aircraft’s thrust.

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The Dryden C-140 JetStar during testing of advanced propfan designs. Dryden conducted flight research in 1981-1982 on several designs. The technology was developed under the direction of the Lewis Research Center (today the Glenn Research Center, Cleveland, OH) under the Advanced Turboprop Program. Under that program, Langley Research Center in Virginia oversaw work on accoustics and noise reduction. These efforts were intended to develop a high-speed and fuel-efficient turboprop system.

Fan Noise Test Facility

The Fan Noise Test Facility built at the Lewis Research Center to obtain far-field noise data for the National Aeronautics and Space Administration (NASA) and General Electric Quiet Engine Program. The engine incorporated existing noise reduction methods into an engine of similar power to those that propelled the Boeing 707 or McDonnell-Douglas DC-8 airliner. The new the low-bypass ratio turbofan engines of the 1960s were inherently quieter than their turbojet counterparts, researchers had a better grasp of the noise generation problem, and new acoustic technologies had emerged. Lewis contracted General Electric in 1969 to build and aerodynamically test three experimental engines with 72-inch diameter fans. The engines were then brought to Lewis and tested with an acoustically treated nacelle. This Fan Noise Test Facility was built off of the 10- by 10-Foot Supersonic Wind Tunnel’s Main Compressor and Drive Building. Lewis researchers were able to isolate the fan’s noise during these initial tests by removing the core of the engine. The Lewis test rig drove engines to takeoff tip speeds of 1160 feet per second. The facility was later used to test a series of full-scale model fans and fan noise suppressors to be used with the quiet engine. NASA researchers predicted low-speed single-stage fans without inlet guide vanes and with large spacing between rotors and stators would be quieter. General Electric modified a TF39 turbofan engine by removing the the outer protion of the fan and spacing the blade rows of the inner portion. The tests revealed that the untreated version of the engine generated less noise than was anticipated, and the acoustically treated nacelle substantially reduced engine noise.

NACA's Lockheed F-94B Starfire with Audio Recording Devices

A Lockheed F-94B Starfire being equipped with an audio recording machine and sensors at the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. The NACA was investigating the acoustic effects caused by the engine’s nozzle and the air flowing along the fuselage. Airline manufacturers would soon be introducing jet engines on their passenger aircraft, and there was concern regarding the noise levels for both the passengers and public on the ground. NACA Lewis conducted a variety of noise reduction studies in its wind tunnels, laboratories, and on a F2H-2B Banshee aircraft. The F2H-2B Banshee’s initial test flights in 1955 and 1956 measured the noise emanating directly from airflow over the aircraft’s surfaces, particularly the wings. This problem was particularly pronounced at high subsonic speeds. The researchers found the majority of the noise occurred in the low and middle octaves. These investigations were enhanced with a series of flights using the F-94B Starfire. The missions measured wall-pressure, turbulence fluctuations, and mean velocity profiles. Mach 0.3 to 0.8 flights were flown at altitudes of 10,000, 20,000, and 30,000 feet with microphones mounted near the forward fuselage and on a wing. The results substantiated the wind tunnel findings. This photograph shows the tape recorder being installed in the F-94B’s nose.

Sonic Inlet for the Quiet Engine Program

Brent Miller, of the V/STOL and Noise Division at the National Aeronautics and Space Administration (NASA) Lewis Research Center, poses with a sonic inlet for the NASA Quiet Engine Program. NASA Lewis had first investigated methods for reducing aircraft engine noise in the mid-1950s. Those efforts were resurrected and expanded in the late 1960s. The researchers found that the use of a sonic, or high-throat-Mach-number, inlet was effective at reducing the noise from the engine inlet. The device accelerated the inlet air to near-sonic speeds which kept the forward moving sound waves away from the inlet. The device also deflected the sound waves into the wall to further reduce the noise. NASA Lewis researchers tested models of the sonic inlet in their 9- by 15-Foot Low Speed Wind Tunnel. They found that the general level of aerodynamic performance was good. The tests during simulated takeoff and landing conditions demonstrated the sonic inlet’s ability to provide good aerodynamic and acoustic performance The researchers then successfully tested two full-scale sonic inlet designs, one from Pratt and Whitney and one from General Electric, with fans. A full-scale engine was installed on a thrust stand to determine the sonic inlet’s effect on the engine’s performance. The amount of noise reduction increased as the inlet flow velocity increased, but the full-scale tests did not produce as great a decrease in noise as the earlier small-scale tests.

Accoustic Casing Treatment Test

Title: W-8 Fan Acoustic Casing Treatment Test on the Source Diagnostic Test Rotor Alone Hardware Program: Advanced Air Vehicles Program (AAVP) Project: Advanced Air Transport Technology (AATT) Sub-project: Aircraft Noise Reduction (ANR) Weekly Highlight: · Acoustic Casing Treatment Testing Completed in the W-8 Single Stage Axial Compressor Facility: Testing of Acoustic Casing Treatments on the Source Diagnostic Test (SDT) rotor alone hardware which had begun in early January was completed on Thursday, February 16th. Four different over-the-rotor acoustic casing treatment concepts were tested along with two baseline configurations. Testing included steady-aerodynamic measurements of fan performance, hotfilm turbulence measurements, and inlet acoustic measurements with an in-duct array. These measurements will be used to assess the aerodynamic and acoustic impact of fan acoustic casing treatments on a high bypass ratio fan at TRL 3. This test was the last of 3 planned tests of potential over-the-rotor acoustic casing treatments. The first treatment test was completed in the Normal Incidence Tube (NIT) at Langley Research Center (LaRC) in Fall 2015 and the second was completed on the Advanced Noise Control Fan (ANCF) in the Aero-Acoustic Propulsion Laboratory (AAPL) in Winter 2016. This work is supported by the Aircraft Noise Reduction (ANR) subproject of the Advanced Air Transport Technology (AATT) Project. (POC: LTV/ Rick Bozak 3-5160)

General Electric 32-Spoke Nozzle on the Convair F-106B Delta Dart

National Aeronautics and Space Administration (NASA) Convair F-106B Delta Dart with a 32-spoke nozzle installed on its General Electric J85 test engine. Lewis acquired a Delta Dart fighter in 1966 to study the components for propulsion systems that could be applied to supersonic transport aircraft at transonic speeds. The F-106B was modified with two General Electric J85-13 engines under its wings to study these components. The original test plan was expanded to include the study of boattail drag, noise reduction, and inlets. From February to July 1971 the modified F-106B was used to study different ejector nozzles. Researchers conducted both acoustic and aerodynamic tests on the ground and in flight. Several models were created to test different suppression methods. NASA Lewis’ conical nozzle was used as the baseline configuration. Flightline and sideline microphones were set up on the ground. The F-106B would idle its own engine and buzz the recording station from an altitude of 300 feet at Mach 0.4 with the test engines firing. Researchers found that the suppression of the perceived noise level was usually lower during flight than the researchers had statistically predicted. The 64 and 32-spoke nozzles performed well in actual flight, but the others nozzles tended to negatively affect the engine’s performance. Different speeds or angles- -of-attack sometimes changed the noise levels. In the end, no general conclusions could be applied to all the nozzles.

Refan Engine in the Propulsion Systems Laboratory

A refanned Pratt and Whitney JT-8D-109 turbofan engine installed in Cell 4 of the Propulsion Systems Laboratory at the National Aeronautics and Space Administration (NASA) Lewis Research Center. NASA Lewis’ Refan Program sought to demonstrate that noise reduction modifications could be applied to existing aircraft engines with minimal costs and without diminishing the engine’s performance or integrity. At the time, Pratt and Whitney’s JT-8D turbofans were one of the most widely used engines in the commercial airline industry. The engines powered Boeing’s 727 and 737 and McDonnell Douglas’ DC-9 aircraft. Pratt and Whitney worked with the airline manufacturers on a preliminary study that verified feasibility of replacing the JT-8D’s two-stage fan with a larger single-stage fan. The new fan slowed the engine’s exhaust, which significantly reduced the amount of noise it generated. Booster stages were added to maintain the proper level of airflow through the engine. Pratt and Whitney produced six of the modified engines, designated JT-8D-109, and performed the initial testing. One of the JT-8D-109 engines, seen here, was tested in simulated altitude conditions in NASA Lewis’ Propulsion Systems Laboratory. The Refan engine was ground-tested on an actual aircraft before making a series of flight tests on 727 and DC-9 aircraft in early 1976. The Refan Program reduced the JT-8D’s noise by 50 percent while increasing the fuel efficiency. The retro-fit kits were estimated to cost between $1 million and $1.7 million per aircraft.

Advanced Combustor in the Four Burner Area

Engineer Frank Kutina and a National Aeronautics and Space Administration (NASA) mechanic examine the setup of an advanced combustor rig inside one of the test cells at the Lewis Research Center’s Four Burner Area in the Engine Research Building. Kutina, of the Research Operations Branch, served as go-between for the researchers and the mechanics. He helped develop the test configurations and get the hardware installed. At the time of this photograph, Lewis Center Director Abe Silverstein had just established the Airbreathing Engine Division to address the new propulsion of the 1960s. After nearly a decade of focusing almost exclusively on space, NASA Lewis began tackling issues relating to the new turbofan engine, noise reduction, energy efficiency, supersonic transport, and the never-ending quest for higher performance levels with smaller and more lightweight engines. The Airbreathing Engine Division’s Combustion Branch was dedicated to the study and mitigation of the high temperatures and pressures found in advanced combustor designs. These high temperatures and pressures could destroy engine components. The Lewis investigation included film cooling, diffuser flow, and jet mixing. Components were tested in smaller test cells, but a full-scale augmenting burner rig, seen here, was tested extensively in the Four Burner Area test cell.

Missile on Display at the 1957 NACA Lewis Inspection

A researcher examines a model being installed in the test section of the 10- by 10-Foot Supersonic Wind Tunnel during the 1957 Inspection of the National Advisory Committee for Aeronautics (NACA) Lewis Flight Propulsion Laboratory. The NACA held its annual Inspection at one of its three research laboratories. Representatives from the military, aeronautical industry, universities, and the press were invited to the laboratory to be briefed on the NACA’s latest research efforts and tour the state- of- the- art test facilities. Over 1700 people visited the NACA Lewis in Cleveland, Ohio during the October 7 - 10, 1957 Inspection. NACA researchers Leonard Obery, seen here, James Connors, Leonard, Stitt, David Bowditch gave presentations on high Mach number turbojets at the 10- by 10 tunnel. It had been only 15 years since a jet aircraft had first flown in the US. Since then the sound barrier had been broken and speeds of Mach 2.5 had been achieved. In the late 1950s NACA researchers sought to create an engine that could achieve Mach 4. This type of engine would require an extremely long inlet and nozzle which would have to be capable of adjusting their diameter for different speeds. A Mach 4 engine would require new composite materials to withstand the severe conditions, modified airframes to hold the longer engines, and high temperature seals and lubricants. The 10- by 10-foot tunnel, which had only been in operation for a year and a half, would play a critical role in these studies. NACA researchers at other facilities discussed high energy aircraft fuels and rocket propellants, aircraft noise reduction, hypersonic flight, nuclear propulsion, and high temperature materials.

Convair F-106B Delta Dart with Research Engines

A Convair F-106B Delta Dart rolls to the right to reveal the two research engines installed under its wings by the National Aeronautics and Space Administration (NASA) Lewis Research Center. Lewis acquired the aircraft in October of 1966 to study inlet and nozzle designs for the supersonic transport engine program. Two General Electric J85 engines were mounted beneath the F-106B’s wings and operated from Mach 1 to 1.5. The right wing always carried reference nozzle for which the performance was known. Six supersonic nozzle variations and two inlets were tested on the left engine. The designs had already been studied in the Lewis wind tunnels, but those tests were limited by shock waves in the tunnels. Most F-106B flights were flown in a 200-mile path over the lake between Buffalo and Sandusky, known as the Lake Erie Corridor. The 1100-mile-per-hour flight took only 11 minutes at an altitude of 30,000 feet. The aircraft almost always returned with a depleted fuel supply so a Visual Flight Rules operation was required. Following the crash of another jet fighter at Lewis in July 1969, the F-106s were stationed at Selfridge Air Force Base in Michigan. NASA pilots flew transport planes each morning to the base before commencing the F-106B missions. After the supersonic transport program was cancelled, the F-106B was used as a test bed for additional engine exhaust nozzle configurations. The F-106B was also used to test inlet configurations for the noise reduction program.

The Doppler Spike of Asteroid 2021 PJ1

This figure represents the 1,000th near-Earth asteroid (NEA) to be detected by planetary radar since 1968. Being only 65 to 100 feet (20 to 30 meters) wide, asteroid 2021 PJ1 was too small to be imaged in any detail, but the powerful 70-meter (230-foot) Deep Space Station 14 (DSS-14) antenna at the Deep Space Network's Goldstone Deep Space Complex near Barstow, California, was able to measure the Doppler frequency of the radio waves that reflected off the object's surface. The data was recorded for 16 minutes between 2:26 p.m. and 2:42 p.m. PDT on Aug. 14, 2021. The figure shows radar echo signal strength on the vertical axis versus Doppler frequency (in units of hertz, or Hz) on the horizontal axis. The strong spike at a value of minus 70 Hz is the reflected signal (or "echo") from 2021 PJ1; the other, smaller spikes are receiver noise, which is like the static on an AM radio if there aren't any nearby stations. Using this information, scientists at NASA's Jet Propulsion Laboratory in Southern California could more accurately calculate the asteroid's velocity, its distance from Earth and its future motion around the Sun. These observations used a prediction – known as an "ephemeris" – that had relatively large uncertainties because the asteroid had been discovered only a few days earlier. If the original prediction had been perfect, the radar echo would appear at zero Hz. The fact that the radar echo is at minus 70 Hz indicates a correction could be made to the predicted velocity of minus 2.7 miles per hour (minus 1.2 meters per second). This measurement also reduced the uncertainty in the asteroid's distance from Earth from 1,300 miles (2,100 kilometers) to 5.2 miles (8.3 kilometers) – a reduction of a factor of about 250. https://photojournal.jpl.nasa.gov/catalog/PIA24563