By Sivapalan Senthooran
Excessive wind noise inside the cabin has been one of the top customer complaints in studies of initial vehicle quality over the last decade. OEMs are continuously trying to improve the wind noise quality of their vehicles to improve passenger comfort. Quite often, manufacturers have to wait for the availability of a physical prototype before they can start improving cabin noise levels. This late in the vehicle design process, however, the engineering cost and available solutions can be very expensive.
Early, design-stage evaluation of wind noise using digital simulation lets OEMs avoid the consequences of discovering and correcting late-stage failures. This approach lets engineers identify issues sooner, before the first prototype is built, to improve designs early – when they are still in work and changes are less costly. Rather than waiting until the end of the design cycle to understand vehicle performance, engineers use simulation to verify that production vehicles will meet the interior noise requirements set for them.
Exa’s digital wind noise solution provides better design solutions to customers while reducing cost and development time by applying computational methods to 3D geometry earlier in the design process. The accuracy and robustness of this solution has been extensively validated and published. Three recent publications are summarized in this blog.
HMC decided to integrate digital wind noise testing into its vehicle development process, as their engineers described in a technical publication , focusing on aerodynamic noise from the side mirror and a-pillar. Exa’s PowerFLOW solution was validated by comparing the numerical predictions to experimental measurements for two production vehicles with different geometry and flow conditions. The outcome of this validation effort is summarized in figures 1 and 2. HMC engineers concluded that the reliability of the PowerFLOW-based digital solution is sufficient for use in their vehicle development process. They also verified that the turnaround time of this digital approach meets their development timeline.
Nissan validated Exa’s wind noise solution on a fully detailed production vehicle for side mirror development and published the outcome in two technical publications [2,3]. Also, the original mirror design was modified based on the guidance offered by simulation, and the improvement was verified in the wind tunnel. The accuracy of predicting the exterior wind noise loads on the entire side glass for side mirror design change is summarized in figures 3-5. The accuracy of predicting interior noise at the driver’s ear at different flow conditions is summarized in figure 6-7. From these studies, Nissan concluded that this wind noise solution can be used with confidence for mirror design improvements to meet wind noise targets, starting from the early stages of the development process.
(L - R) Figure 3: Mirror configurations, Figure 4: Mirror design trends, and Figure 5: dB maps of wall pressure fluctuations for baseline.
(L - R)Figure 6: Vehicle model, Figure 7: Interior Noise for different speeds.
A technical publication by Exa discusses one of the most commonly used productive usage scenarios for side mirror designs . In this study, two different side mirror designs were evaluated for a given vehicle design. The performance of the mirror designs was evaluated using interior noise levels at driver head location, as shown in figures 8-11. Flow analysis was performed to understand why one mirror performed better than the other mirror, so that mirror designs can be further improved.
(L - R) Figure 8: Mirror configurations, Figure 9: Mirror design trend.
(L - R) Figure 10: Acoustic loads on aide glass for 500-5000 Hz, Figure 11: Acoustics from side mirror for 500-5000 Hz
The accuracy and robustness of Exa’s digital wind noise solution, combined with its noise source identification capabilities and fast turnaround time, enable the use of this solution early in the design process. This complete solution is currently used by most OEMs, early in their vehicle design process, to improve the wind noise performance of their vehicles.
To read more about Exa's greenhouse wind noise solution, download the whitepaper found at: http://exa.com/en/whitepaper-greenhouse-wind-noise
- K.D. Ih, S.R. Shin, S. Senthooran, B. Crouse, D. Freed, “Activities of Digital Wind Noise Testing Process for Virtual Prototype Development”, JSAE 2009-5476.
- D. Lepley, S. Senthooran, D. Hendriana, T. Frazer, "Numerical Simulations and Measurements of Mirror-Induced Wind Noise," SAE 2009-01-2236.
- D. Lepley, A. Graf, R. Powell, S. Senthooran, “A Computational Approach to Evaluate the Vehicle Interior Noise from Greenhouse Wind Noise Sources”, SAE 2010-01-0285.
- R. Mutnuri, S. Senthooran, R. Powell, Z. Sugiyama, D. Freed, “Computational Process for Wind Noise Evaluation of Rear-View Mirror Design in Cars”, SAE- 2014-01-0619.