Part 1: Aeroacoustics Made Simple: When Air Becomes Sound

Picture this: it is a busy workday, your laptop is running multiple applications, and suddenly the whirring of the fan is louder than everything else on your desk. The noise is familiar, even ordinary. But behind that small everyday irritation is a surprisingly rich engineering problem: air is moving, pressure is fluctuating, and those fluctuations reach your ears as sound.

That is aeroacoustics: sound generated by airflow, turbulence, or aerodynamic forces interacting with surfaces. The word may sound complex, but our experience of it is simple. Whenever air moves around an object and creates noise, aeroacoustics is involved.

Why Aeroacoustics Is a Good Introduction to Multiphysics

Aeroacoustics is also one of the clearest ways to understand what engineers mean by the term “multiphysics”. Multiphysics problems arise when a single branch of physics is not enough to fully capture real-world phenomena mathematically. Instead, different physical effects interact: airflow changes pressure, pressure fluctuations generate sound, surfaces influence the flow, and the resulting acoustic field depends on all these interactions.

Consider an example of a flag moving in the wind. The materials and structural shape of the flag affect how airflow bends the flag, the flag’s motion changes the airflow, and the changed airflow produces new forces on the flag, which may make an audible sound as it snaps and ripples. That feedback loop is an example of coupled physics. Aeroacoustics follows the same principle: how does moving air become audible noise?

From Vibroacoustics to Aeroacoustics

Before looking more closely at aeroacoustics, it helps to separate it from vibroacoustics. In vibroacoustics, a structure vibrates first, and that vibration radiates sound into the surrounding air. A guitar is a familiar example: the strings vibrate, the guitar body responds, and sound is produced.

In aeroacoustics, the primary source is the moving air itself. Think of the wind noise around a car’s side mirror, the sound from a drone propeller, the hum of a cooling fan, or the noise generated by air moving through HVAC equipment. The structures may shape the flow, but the sound begins with pressure fluctuations in the air.

Why Aeroacoustics Matters

Aeroacoustics matters because unwanted noise is rarely just a comfort issue. In automotive design, wind noise affects the cabin experience. In aerospace, fan, jet, and airframe noise influence passenger comfort and environmental compliance. In electronics cooling, fans must manage thermal performance without creating disruptive noise. In renewable energy, wind turbine noise can shape community acceptance. In some cases, noise may even affect whether or not a design meets regulations and can be built.

Across these applications, the engineering goal is often the same: understand where the noise is coming from, how it travels, and how design changes can reduce it without compromising performance.

Why Simulating Aeroacoustics Is Not as Simple as Reading CFD Pressure

At first glance, aeroacoustics may seem like a straightforward extension of computational fluid dynamics (CFD). If a simulation already computes pressure and velocity, why not just look at the pressure field and identify the noise?

The challenge is scale. The acoustic pressure associated with sound is extremely small compared with the aerodynamic pressure fluctuations created by turbulent flow. For example, a sound pressure level of 75 dB corresponds to a pressure fluctuation of roughly 0.11 Pa in air, while the flow around a vehicle at highway speed can involve much larger aerodynamic pressure variations. Finding the acoustic signal inside that flow field can be like trying to hear a pebble drop in the middle of a stormy sea.

That is why aeroacoustic simulation needs more than a basic pressure plot. Engineers must decide how much flow detail is needed, how acoustic sources should be extracted, and how sound should be propagated to the listener or receiver location.

So, Is Aeroacoustics Really That Hard?

Aeroacoustics can be mathematically complex, but the core idea is intuitive: moving air creates pressure fluctuations, and some of those fluctuations become sound. Once that is clear, the engineering problem becomes easier to frame. The key is not to simulate everything at the highest possible fidelity, but to choose the right method for the design question.

In Part 2, we will look at the main ways engineers simulate aeroacoustics, from direct and hybrid methods to faster SNGR-type approaches, and how to choose the right level of fidelity for the design question.

Written by Vicky Tsianika, Product Management Director, and co-authored by Nicolas Driot, Senior Principal Product Manager.