Postdoc MyungJun Song (left) and doctoral student Allie Gagne work in the Short Takeoff and Vertical Landing (STOVL) lab at the Florida Center for Advanced Aero-Propulsion (FCAAP) in the Aero-Propulsion Mechatronics & Energy (AME) building at FAMU-FSU College of Engineering in Tallahassee, Florida. (Scott Holstein/FAMU-FSU College of Engineering)
College researchers publish findings in the Journal of Fluid Mechanics; work could lead to methods for reducing intense noise that threatens aircraft and ground crews
Researchers at the FAMU-FSU College of Engineering have developed a new model for understanding how supersonic jets of air collide with the ground or other structures to create a resonant feedback loop that produces extreme and potentially dangerous noise levels, a breakthrough with significant implications for military aviation safety.
The research, conducted in collaboration with the Florida Center for Advanced Aero-Propulsion (FCAAP) and published in the Journal of Fluid Mechanics, examined jets like those found in Short Takeoff and Vertical Landing (STOVL) aircraft, such as the F-35B Lightning II. The ability to operate without a traditional runway gives these aircraft critical tactical advantages, but as they descend toward the ground, exhaust plumes interact with landing surfaces and generate intense noise, often exceeding 140 decibels, which poses serious dangers to both aircraft structure and nearby personnel.
“Only a tiny fraction of the jet’s energy is transformed into sound, but this small fraction has a major impact,” said Farrukh S. Alvi, professor in the Department of Mechanical and Aerospace Engineering and former founding director of the Institute for Strategic Partnerships, Innovation, Research, and Education (InSPIRE) and founding director of FCAAP. “The intense noise produced by jet engines can cause structural damage to the aircraft and damage the hearing of personnel on the ground. We are trying to understand the physics behind these supersonic jets and the noise they produce so that we can develop tools that can reduce their impacts. In fact, we have already had some success in developing techniques that can reduce jet noise.”
Supersonic Jet Noise Poses Structural and Safety Risks Exceeding 140 Decibels
When high-speed air from jet engines mixes with ambient air, it creates large-scale disturbances that hit the ground, producing strong sound waves that propagate back toward the jet engine. This establishes a repeating, back-and-forth interaction—a feedback loop—causing loud and repeating resonant noise. For aircraft, these resonant vibrations accelerate structural fatigue and can generate hazardous low-pressure zones that pull the aircraft toward the ground.
For crewmembers on the ground, sustained exposure to sound levels over 140 decibels can cause permanent hearing damage, even when wearing protective equipment. At peak intensities, extreme acoustic pressure can cause organ damage.
Acoustic Standing Waves Found to Govern Noise Pitch in Supersonic Impinging Jets
The research team tested a supersonic, Mach 1.5 jet—1.5 times the speed of sound—and adjusted nozzle pressure and the jet’s distance from the ground to simulate takeoff and landing conditions across a range of measurements.
To visualize the airflow, they used a high-speed camera and schlieren imaging, a specialized technique that allows researchers to see the jet flow, including its large-scale disturbances and the sound waves generated in real time. A highly sensitive microphone simultaneously recorded the sound produced by the jet.
When the jet is loud, the jet flow and sound waves repeat at a regular rhythm—a characteristic of a resonant cycle. By matching images to a specific point in the cycle, the researchers developed a clear picture of the airflow and measured how fast large-scale disturbances moved and how sound waves traveled back toward the nozzle.
The researchers found that for many cases, the pitch of the noise was primarily governed by acoustic standing waves, which appear stationary in space between the body of the plane and the ground. The findings reveal that pitch is not primarily governed by disturbance velocity, offering another perspective on the existing understanding of resonance feedback. They also found that slower disturbances tend to be larger and consequently create louder noise.
“That was surprising,” said postdoctoral researcher Myungjun Song, the study’s lead author. “We found that these acoustic standing waves are much more important in determining the pitch, while the size and speed of the disturbances decide the level or ‘loudness’ of the noise produced.”
Because disturbance speed has little effect on pitch, information about acoustic standing waves is sufficient to predict noise pitch—a key insight that enables engineers to predict noise frequencies more easily during aircraft and landing pad design, a critical step toward protecting both aircraft structures and personnel from acoustic trauma.
FCAAP Facilities at FAMU-FSU College of Engineering Enable Cutting-Edge Aerospace Research
The experiments were conducted at FCAAP’s specialized research facilities at the FAMU-FSU College of Engineering, designed for advanced high-speed aerodynamic studies. Researchers used the FCAAP STOVL facility, which offers cutting-edge flow diagnostic capabilities, and the hot jet facility, which can generate high-temperature, high-speed airflow in an anechoic chamber for highly accurate acoustic measurements under realistic jet conditions.
“While jet propulsion is an important focus of our work, our research is not limited to it,” Alvi said. “The university and the college, through FCAAP, operates a polysonic wind tunnel that simulates supersonic flows up to Mach 6, which is supersonic to hypersonic conditions. We also use our anechoic wind tunnel and subsonic wind tunnels for numerous other aerospace related research projects. Together, these facilities and the expertise of our researchers create a one-of-a-kind ecosystem for conducting leading-edge research in aerospace and aviation.”
An associated initiative, InSPIRE is an FSU-led effort to establish a new aerospace and advanced manufacturing hub in Bay County, Florida. The program builds on FCAAP’s foundation to develop complementary facilities for larger hypersonic wind tunnels capable of handling a wider range of conditions for applied, industry-relevant research.
“In partnership with industry, InSPIRE is also integrating advanced manufacturing capabilities that will allow much more efficient test and evaluation and assist our industry partners to innovate manufacturing processes in a realistic factory-modeled setting,” said Alvi. “Working with industry partners allows our researchers to use their expertise to solve the pressing and difficult problems that are directly relevant for industry.”
Funding and Collaborators
The project was a collaborative effort involving Song, the study’s lead author; Alvi; and graduate student Serdar Seçkin. Funding was provided by the Office of Naval Research, with additional support from the National Science Foundation, the Air Force Office of Scientific Research, FCAAP, the FAMU-FSU College of Engineering and the Don Fuqua Eminent Scholar Fund.
Editor’s Note: This article was revised with the assistance of an AI editing tool for the purpose of structural reorganization, AP style compliance and SEO/GEO optimization. All facts, figures and direct quotations are unchanged from the original article published March 25, 2026, by Florida State University News. Editorial judgment and final review remain the responsibility of the FAMU-FSU College of Engineering communications staff.
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