Mar 16, 2021 / Overture

The new sound of supersonic: Q&A with Boom’s Principal Acoustic Engineer

Acoustics expert Joe Salamone shares a deep dive into the science of building quieter supersonic aircraft.

Joe Salamone is shaping the future of acoustics in supersonic aircraft design. As Boom’s Principal Acoustics Engineer, he supports the teams designing Overture, the company’s supersonic commercial airliner. With a Ph.D. in acoustics from Penn State, industry awards for sonic boom research, and 20 years experience at Gulfstream Aerospace, Salamone is uniquely positioned to ensure noise considerations are deeply-rooted in Overture’s design.

Salamone joined Boom at a pivotal time in Overture’s development. His primary focus is providing the acoustics data that is helping engineers design a quieterand hence more sustainableaircraft. On any given day, he conducts aircraft noise research, provides aircraft environmental noise considerations, supports the company’s collaborations with Rolls-Royce and Collins Aerospace, and lends his expertise to Boom’s policy and sustainability teams.

We sat down with Salamone to learn more about the acoustic intricacies of building a quieter, sustainable supersonic aircraft.

From an acoustics standpoint, what are the most significant aspects of Overture’s design — so far?

The most significant component for Overture’s environmental noise progress is not going to come from any one or even two specific pieces of hardware installed on the aircraft. The biggest impact will come from our design philosophy and the willingness of our team to very seriously weigh environmental noise requirements, triggering changes to other aspects of aircraft design. These changes, or tradeoffs, are worth making in order to build a more sustainable aircraft.

Will Overture sound like today’s airliners?

Overture’s environmental noise will blend in with the existing subsonic aircraft fleet. Overture won’t have afterburners like Concorde and its jet exhaust will be subsonic during take off. This means no loud shocks in its exhaust plume, like you would typically hear and see from supersonic military aircraft.

During every step of Overture’s design, we’re taking into account community concerns and working hard to ensure that people on the ground will not experience increased overall noise exposure due to Overture. If we do our job correctly, people won’t be able to hear the difference between Overture and today’s subsonic airliners.

What is your current focus with the Overture team?

I’m working with the engineering teams, assessing noise considerations that will influence aircraft design. Our focus is designing Overture to operate as sustainably as possible, and that includes environmental noise emissions.

I’m also supporting our collaborative work with Rolls-Royce and Collins for the acoustics efforts. Each of those respective companies are very well known for their acoustics capabilities. Along those lines, I also partner with our policy and sustainability teams in their regulatory activities.

What is your role in aircraft design?

I provide guidancedata and researchto ensure important noise considerations are integrated into every aspect of Overture’s design and development. But, I’m not actually designing the aircraft. Overture’s quieter noise levels will be the outcome of hard work from our design team.

Ultimately, my role is to provide our engineering, policy and sustainability teams with the data and requirements they need to do their jobs.

Salamone’s doctoral research explored the sonic boom. Picture here is an unpublished graphic from his research: a notional acoustic pressure field of a focused sonic boom within the focal zone. The plot is used to predict the amplitude of a sonic boom that undergoes sonic boom focusing. It demonstrates both the amplification and decay of sound as a function of frequency and relative distance from the focusing location. Note that Overture will only fly supersonic over the ocean to avoid sonic boom impact above populated areas.

What design considerations will reduce Overture’s environmental noise emissions?

We’re evaluating engine design elements, such as mixers and chevrons, that reduce jet noise. In addition, we will incorporate acoustic absorbing material on the inside of the engines to reduce fan noise, core noise and turbine noisesimilar to what’s done in subsonic aircraft. We’re also including airframe noise designs for landing gear and high lift devices to ensure a comprehensive approach for reducing environmental noise.

What might surprise people is that Overture will have the capability to automatically regulate the engine thrust for reduced noise on take off, yet still achieve all necessary performance and safety requirements. Multiple noise abatement procedures during takeoff and landing will also minimize noise.

Are you running acoustic simulations for Overture?

We’re computing first-order estimates for Overture’s environmental noise, which offers the fastest means to evaluate possible airframe/engine configurations. Each primary noise component is modeled using publicly available databases from the open literature. The team leverages past research and testing for each of the significant sources of noise on the airframe and the engine.

A moving monopole animation demonstrating a moving sound source traveling above a hard surface at a constant subsonic speed. Sound waves propagate away from the source and simultaneously reflect off the hard surface while the sound source is moving over and away from the left to the upper right. The animation demonstrates two primary components of physical acoustics. First, it shows constructive and deconstructive interference resulting from the superposition of the moving source and its mirror caused by reflection from the hard surface. Second, it demonstrates asymmetry in the location of the source relative to the spherical wavefronts. The peaks and valleys emanating from the source on the right side (ahead of it) are closer together than the peaks and valleys to the left of the source (behind it). When measured, that phenomenon would be observed as a Doppler shift.

Our noise evaluation process characterizes each source in the engine and airframe, then combines them together to make a prediction of what it sounds like at the ground as the aircraft takes off and lands. It accounts for atmospheric and ground effects, aircraft motion, and the proximity of the aircraft noise sources to the receiver location near the ground.

We’re conducting noise assessments for Overture configurations to evaluate “trades” among the engineering disciplines, balancing fuel burn considerations with cruise performance, take off/landing capability, noise and many other factors. We’re increasing the fidelity of noise analysis as we hone in on the most prominent Overture configurations. This approach ensures the team always has an acoustic evaluation that is consistent with the level of maturity of the aircraft design.

How does your role drive Boom’s commitment to sustainability?

In addition to supporting the engineers designing Overture, I work with our policy and sustainability teams to advocate for data-driven noise standards for supersonic aircraft.

One of the most important ways Boom can contribute to the development of new supersonic noise standards is to provide credible data to the regulatory bodies creating those standards. My role is to help provide the necessary data that our sustainability team can use when interfacing with international and domestic regulatory organizations.

At present, there are no noise standards specific to supersonic aircraft, including for take off and landing. There are many aspects in common between noise certification for today’s subsonic airliners and supersonic aircraft. However, the subsonic performance of supersonic aircraft is very different to that of a subsonic aircraft. This disparity plays an important role in characterizing and assessing noise generated by supersonic aircraft as they takeoff and land. Having that datathe noise levels of a supersonic airliner flying subsonicallywill be essential for the regulatory bodies that create robust standards.

Atmospheric absorption is a physical process that engineers consider when making environmental noise predictions for aircraft. Pictured here is a notional plot of atmospheric absorption as a function of ambient temperature and relative humidity using the standard provided for noise certification. Since aircraft fly in atmospheric conditions where the temperature and relative humidity often vary with altitude, atmospheric absorption will also vary with altitude.

What inspires your work in aviation and aerospace?

Throughout my career, I’ve been very fortunate to have worked with passionate individuals who made significant contributions to aviation and aerospace. I’ve also collaborated with many people at universities and government agencies who demonstrate high levels of dedication and commitment to their roles in helping us understand and improve aviation noise.

People who work on new products or tackle difficult challenges tend to be very driven individuals. It’s humbling to be around people who have spent countless hours dedicated to making their projects succeed. I wouldn’t be where I am today without their mentorship, leadership and inspiration. It’s exciting to bring this knowledge to Boom and Overture, where I am equally humbled by an extremely skilled and talented team of highly motivated people.

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