Acoustic simulation advances help manufacturers innovate to cut transport noise

Mont-Saint-Guibert, Belgium, December 12, 2019 – Free Field Technologies, part of Hexagon’s Manufacturing Intelligence division, today announced the Actran 2020 suite comprising new acoustic, vibro-acoustic and aero-acoustic technologies that enable aerospace and automotive manufacturers to build more accurate noise production and optimization into their design processes.

Aircraft operators face growing restrictions on noisy aircraft and more stringent International Civil Aviation Organization (ICAO) noise management regulations. Reducing noise has become a business priority due to landing fees, flight curfews, or fleet being excluded from some airports. This is driving aerospace innovation, with engine technology paramount for effective aircraft noise reduction.

At the intake, engine noise is dependent on both the axial flow through the turbo fan and the associated swirl, but the combined effect on noise propagation was historically challenging to model. Actran’s award-winning aircraft engine noise prediction [1] now automatically accounts for the mean flow swirl component in acoustic duct modes excitation, which avoids mismatches between nacelle inlet flow and boundary conditions. The more accurate simulation enables engineers to understand how design changes such as shortening the nacelle affect noise emissions so they can optimise the placement of acoustic treatments.

Figure 1 - Impact of flow swirl consideration in acoustic duct mode propagation

At the exhaust, simulating the indirect combustion noise of aircraft engines was rarely feasible due to the cost of computation. The Cumpsty and Marble compact model is now implemented in Actran, applying inexpensive modelling to assess indirect combustion noise in a turbomachine. Recently developed and validated against measurements together with Safran Helicopters Engines [2], the model enables manufacturers to predict the combustion noise emitted in engines.

The forthcoming ISO 360-1 standard reflects growing pressure to reduce automotive pass-by noise, with tyre noise expected to contribute 60% by 2024. A new dedicated noise assessment utility in Actran maps rotating tyre time domain vibrations from frequently used tools such as Abaqus onto a tyre-deformed mesh. This model is transposed into the frequency domain to predict tyre noise radiation in-situ so that acoustic mitigation solutions can be optimized accurately within a single acoustic engineering environment.