PowerACOUSTICS: The first Validated Interior Noise Prediction Solution for Wind Noise

New Functionality in PowerACOUSTICS 1.1:

Audio Signal Synthesis

• Create audio .wav files from simulated results (SPL files)
• Multi-clip capability with specified duration
• Any spectrum may be auralized (including structural acoustic data) by writing audio files

Spectral Conversions

• Sum energy from narrower bands into wider bands
• Interpolate spectrum energy from wider bands into narrower bands

Overall Metrics for Sound Quality Ranking

• Overall dB or dB(A)
• Loudness in sones (free-field or diffuse-field)

Consumers Simply Don't Want to Hear it

J. D. Power and Associates’ initial quality surveys indicate that wind noise is consistently the number one consumer complaint, directly impacting consumer brand loyalty and vehicle sales. Reducing interior noise levels to achieve occupant comfort is therefore at the forefront of acoustic engineers’ concerns. A significant amount of engineering time and product cost is spent on acoustic testing and fixes to achieve the interior noise targets required for highly rated, quality competitive products.

In the past few years, great strides have been made in reducing powertrain, road, and tire noise leaving wind noise as the dominant noise source during high speed travel, and thus an increasingly important area for ground transportation acoustic engineers to address.

PowerACOUSTICS enables interior wind noise analysis of exterior shape changes, glass properties and interior acoustic package modifications to minimize sound at an occupant’s ear.

Seeing & Hearing Noise Before it Happens: A CHALLENGE

Interior noise levels  are typically not assessed until late in the development process when prototypes are built. This is often too late to make significant changes to the product design—requiring late stage design re-work or sound package upgrades such as thicker and/or laminated glass, adding significant cost and weight.

Acoustics engineers face numerous challenges: acoustic wind tunnel tests are expensive, flow visualization and noise source identification are difficult, and testing is not possible until physical prototypes are available. A numerical simulation approach is highly desirable for early design assessment. However, most available numerical solvers do not provide accurate prediction of complex transient turbulent flow, required for effective acoustic simulation. Exa’s unique transient and compressible flow solver technology allows engineers to simulate and visualize the flow-induced sources of noise and resulting transient pressure loading on the external surfaces.

Exa now provides a complete digital solution with PowerACOUSTICS™, the only validated interior noise prediction tool for external air flow. PowerACOUSTICS enables aeroacoustics and noise control engineers to efficiently collaborate to optimize the vehicle exterior shape and sound package design to meet interior noise targets.

PowerACOUSTICS, paired with Exa’s PowerFLOW, enables accurate pressure fluctuation prediction, noise source identification, wind noise transmission to interior, and sound package parameter study capabilities—all with an extensively tested and validated solution.

Interior Noise Prediction Easily Integrated into your Product Development Process

PowerACOUSTICS seamlessly integrates into the workflow throughout the product development life cycle. With the new capability to simulate interior noise during early-stage design trade-off studies, wind noise engineers can now cooperate with aerodynamics and packaging colleagues to rank design themes, optimize exterior shape across attributes and participate in target setting for sound package. Later in the development process, PowerACOUSTICS can be used to screen shape design variables, for example, on side mirrors, thus reducing the amount of testing traditionally performed in aeroacoustic wind tunnels. Finally, in resolving issues that may come up during final prototype testing, the flow visualization provided by PowerFLOW and panel contribution analysis from PowerACOUSTICS make it easier to understand why a particular fix is effective, raising confidence during the decision-making process late in development.

PREDICT INTERIOR WIND NOISE Fully embedded SEA solver makes it easy to predict noise spectra at occupant’s head location generated by exterior wind pressure fluctuations. Easy to use graphical user interface makes case setup fast. Users walk through GUI establishing cabin type, panel parameters, and graphing preferences
	PRESSURE FLUCTUATION PREDICTION Exa’s PowerFLOW provides accurate exterior pressure fluctuations on the greenhouse panels for load input to PowerACOUSTICS. These pressure fluctuations are calculated on fully detailed geometry and simulations may also easily be performed in yawed  flow conditions.
NOISE SOURCE IDENTIFICATION PowerACOUSTICS provides insight into noise sources resulting from complex exterior flow structures. Panel contribution to interior sound is graphed across frequency bands.
	SOUND PACKAGE PARAMETER STUDIES PowerACOUSTICS allows acoustics engineers to rapidly set up glass and cabin properties for interior noise spectra calculations. Evaluate the effect of various noise dampening options such as varied monolithic glass thicknesses versus laminated glass in seconds. Easily identify the contribution from each panel to the overall sound heard by the occupant.

Enhanced Design Process

Compressed development cycles and pressure on engineering expenses has greatly reduced the number of high quality prototypes available for accurate assessment with aeroacoustic wind tunnel testing. PowerACOUSTICS coupled with PowerFLOW provides aeroacoustics and interior noise performance information early enough to impact design and reduce the amount of late design changes and physical testing. Automated visualization analysis of PowerFLOW results gives insight into the flow behaviors responsible for the exterior pressure loads—something not even possible with a wind tunnel test.

The Validated Solution Based on extensive validation, PowerACOUSTICS’ users may confidently rely on results and proceed with design recommendations to reduce noise levels.  Right: Excellent correlation: Cross plot of predicted interior wind noise from PowerACOUSTICS versus experimental results for the 500 to 4000Hz octave bands from 30 test cases.