By Vincent Le Goff
In the automotive industry, it’s not what you hear – it’s what you don’t hear – that matters the most to vehicle safety and comfort. Advancements in aeroacoustics have helped engineers dramatically reduce the main noise contributors of passenger cars, including engine, rolling, and aerodynamic noise. This calls new attention to what suppliers and OEMs are doing to address the challenges of acoustic efficiency (or inefficiency) across other components and subsystems as a way of differentiating themselves in the driver experience department.
Some of the top challenges in this quest for quiet come from rotating machines, such as engine cooling fans and Heating Ventilation and Air Conditioning (HVAC) blowers, which require a cautious evaluation of their acoustic performance during the design process. While experimental methods have historically been used to reduce the most obvious noise sources, they have also shown limitations – such as time and cost to build prototypes, and mechanical and aerodynamic constraints. Additional complications, including the ambitious targets set by car manufacturers and a lack of insight into acoustic phenomena on the part of automotive suppliers, further limit opportunities for innovation.
Examining new ways to overcome these challenges was the goal of a joint publication from Mahle Luxembourg and Exa. At the Fan 2015 Conference, the team presented how a digital approach to acoustic analysis can help reduce these constraints and offer a better understanding of – and ability to control – noise generation mechanisms. Leveraging the transient and compressible properties of Exa PowerFLOW simulations, the team could accurately predict the aeroacoustics performance of an HVAC blower up to 5 kHz (within 0.5dB overall from experimental data), and perform a detailed analysis of the noise sources and the possible flow mechanisms at their origin.
Experimental setup (Left) - Acoustic Power radiated by the blower (Middle) - Noise sources analysis from the simulation (Right)
The study analyzed aerodynamic pressure fluctuations in the flow field filtered in the frequency range 750-1050 Hz, which highlighted the regions in the blower with significantly higher noise levels. Transient analyses including animations of the unsteady velocity field and vortex cores inside the casing helped identify remarkable flow features at the location of these high levels. The team observed strong recirculation of the flow between the blower casing and the fan, both at the tip and the root of it, as well as a significant shear layer developing at the cooling channel of the motor – emphasizing the importance of the casing and the wheel design in these areas.
As shown in this study, integrating digital methods into the development process of fan and blower systems not only provides for the accurate evaluation of their acoustic performance before the first prototype is even built, but it also gives essential information about the critical design parameters to adjust for further product optimizations. Digital simulation leveraged throughout fan system development together with new options for cloud computing stand to offer suppliers and manufacturers alike a new competitive advantage in their quest for quiet.
Learn more about this joint study here.
“Towards a full digital approach for aeroacoustics evaluation of automotive engine cooling fans and HVAC blowers”, B. Le Henaff, D. Pihet, M. Piellard, V. Le Goff, Fan 2015, Lyon, France, April 15-17. Available: https://www.springerprofessional.de/en/a-digital-approach-to-the-aeroaco...(October, 2017)