Using Simulation and Aeroacoustics to make for quieter flights.

Reducing the ‘Big Racket’ of Airplanes

The study of the sound associated with our airplanes, also known as aeroacoustics, is a complicated business. It not only covers the sound you would hear in the plane, it studies the sounds heard from bystanders on the ground. Noisy airplanes can make for unhappy customers, sleepy pilots and a “not in my back yard” attitude. With the use of simulation, though, we can all watch the skies without hearing them as well.

Noises travel to our ears as distortions of the air around us. It is therefore no surprise that turbulent flow through the air, such as by landing gear, can cause quite a racket. “Landing gear, being an essential part of the plane,” remarks Fred Mendonça, a member of CD-adapco’s technical organization, “sticks out like a bluff body and violently disturbs the airflow creating noise and drag. This doesn’t greatly affect fuel consumption, but it does account for 35-40% of the noise associated with landings. Other landing configuration components like the deployed slats and flaps of the wing will account for another 35-40%.”

Having contributed 70-80% of the aircraft’s noise, it is no wonder that these areas of the plane have many aeroacoustics studies associated with them.

Mendonça adds that, “Simulation software, like STAR-CCM+, can act as a virtual wind tunnel at a fraction of the cost. You don’t need to make a physical model, book time at a wind tunnel, and borrow wind experts to run the equipment. Just take your CAD model and perform the analysis in the computer, you can even easily tweak and test the new design. This will allow you to understand the flow around the area and the noise generation mechanisms.”

The noise doesn’t stop at the wing; cooling racks and internal air circulation ducts will also contribute to the racket. “A cockpit has a lot of electronics and will therefore produce a lot of heat. Air channels are needed for active cooling. Compressed air, bled into the cabin compartment to maintain cabin pressure and temperature, create noise in the delivery ducts and discharge nozzles,” explains Mendonça.

This air will pass through many passageways and ducts, each time it turns or passes through an orifice turbulent flows can be created, ultimately producing noise.  “Once we simulate the airflow, we can modify the design to limit noise,” said Mendonça.

He adds that “even low noise exposure over a long time can cause fatigue. This becomes a safety issue. There is the same issue in cars and trains. It attributes to why commercial pilots and truck drivers have a limit on how long they can operate the vehicle. If you have a manufacturer which supplies low noise vehicles, then they can be operated more comfortably, safer and for longer.”

The major difference between the acoustics simulations around the plane and the simulations within the ventilation is a point of reference. Instead of creating a wind tunnel for the plane to “fly through,” you now are making a smaller wind tunnel to represent the inside of the vent. Essentially, the CFD model will be solving the same equations.

However, pilots are not the only thing associated with fatigue when vibrations are involved. Portions of the plane can experience structural fatigue due to aerodynamic flow. “Any vibrations will cause fatigue stress,” said Mendonça. “But if resonance modes are excited then you have more of an issue like possible component fatigue failure.

I’m not sure DaVinci knew how noisy his dream of flight might be – but I’m sure he’d be proud of modern industry for using simulation to ease the natural trial-and-error of the scientific process.

Source: Fred Mendonça, CD-adapco

Images from Tabesh et al. Numerical Investigation of 1/3- and Full-Scale

Partially-Dressed Small Business Jet Landing Gears”, AIAA-2012-2236

Written by

Shawn Wasserman

For over 10 years, Shawn Wasserman has informed, inspired and engaged the engineering community through online content. As a senior writer at WTWH media, he produces branded content to help engineers streamline their operations via new tools, technologies and software. While a senior editor at, Shawn wrote stories about CAE, simulation, PLM, CAD, IoT, AI and more. During his time as the blog manager at Ansys, Shawn produced content featuring stories, tips, tricks and interesting use cases for CAE technologies. Shawn holds a master’s degree in Bioengineering from the University of Guelph and an undergraduate degree in Chemical Engineering from the University of Waterloo.