New York, London and Stuttgart. July 9, 2010

The reduction of aerodynamic noise has long been a design concern throughout the automotive, rail and aerospace industries. Exposure to extraneous noise generated by acoustically non-optimal designs not only detracts from ride enjoyment, but also contributes significantly to driver fatigue.

CD-adapco, the world’s leading supplier of engineering simulation solutions to the automotive industry, has demonstrated a first in fluid-structures integrated capability for aeroacoustics simulations with structural impedance effects. CD-adapco is collaborating with the Aeroacoustics Working Group of German automotive manufacturers, which has issued the following statement:

“The consortium of the German automotive manufacturers Audi, BMW, Daimler, Porsche and Volkswagen, that cooperates for improved numerical aeroacoustic tools, considers the results of the structural impedance effects using the coupled Finite Volume flow and stress analysis to be a well conceived and practical solution and encourages CD-adapco to continue validation against the performance data which has been made available in this project.”

CD-adapco's flagship software, STAR-CCM+, is unique in its ability to perform fully coupled fluid-solid interaction. It uses a finite volume solid stress solver implicitly integrated with the finite volume flow solver to analyze the acoustical damping effects of flexible materials.

A particularly pernicious source of noise is that associated with sunroof (or side-window) buffeting, which is caused by unsteady flow over the sunroof opening interacting with the roof panel, and radiating sound to the vehicle occupants. STAR-CCM+ has been extensively compared with sunroof buffeting measurements on the industry standard SAE-body, modified to include a sunroof cavity with different roof materials – including Aluminum, Perspex and Plywood. The simulations correctly predicted that the noise level which the driver hears can be reduced by to 10dB (decibels) at the peak frequency, illustrating how the flexibility of the roof panel is able to absorb acoustical energy to quiet the passenger experience.

The simulation results showed how the flow becomes unsteady behind the leading edge of the sunroof opening, creating a vortex which travels downstream and impacts the rear roof panel behind the sunroof opening. One way to design against this phenomenon is to add deflectors to change the flow pattern over the opening, often by introducing additional mechanical parts. By changing the acoustic properties of the car panels, similar noise reductions can be achieved.

By working closely with car manufacturers, CD-adapco provides validated tools to predict and design against wind-induced noise early in the design process, resulting in more refined vehicles that are more comfortable and ultimately safer to drive.