Predicting flow-induced noise in vehicle components and systems is now possible using new technology from Exa Corporation
A revolutionary new technology developed by Exa Corporation enables clear indentification of the aeroacoustic noise sources in simulation. This patent-pending feature called FIND (flow-induced noise detection) is implemented within the Exa PowerAcoustics software.
“Previous methods were requiring a lot of training on how to extract the practical information from the flow results on where to modify the design in order to reduce noise,” says Franck Pérot, senior director of acoustic applications at Exa.
Engineers at Exa have implemented advanced algorithms, which can quantify each individual vortex in the flow. “We had to go back to the DNA of the flow-induced noise mechanism. Part of that is understanding and quantifying the dynamics of the turbulence, so that we can restructure the acoustic power radiated by these fundamental mechanisms,” Pérot explains.
The FIND feature can also analyze the fluid flow of a design and highlight the different noise levels at each region. This enables engineers to identify the main contributors to the radiated noise. Generated noise can also be listened to before and after design modifications, so that the impact of any proposed improvements can be heard.
“To validate the tool,” Pérot says, “we took a number of test cases and production cases for which the noise levels were known from measurements and ran PowerFlow to obtain reference simulation results. At this point, we knew the noise sources predicted with FIND were correct. The next step for us was to look at different modifications to check if the tool was indeed able to guide the design. When we checked the output power of FIND, we got the correct trends in terms of decibel differences giving us the confidence in the ability to characterize different designs.”
FIND is particularly useful for predicting the noise sources for areas such as greenhouse or underbody wind noise, and HVAC and blower noise, or noise from within exhaust systems.
Collaboration with BMW
In close collaboration with Exa, BMW Group has already used the new tool to perform aeroacoustic evaluations of complete HVAC systems (see image top). BMW had previously found that analysis of the flow through standalone components such as ducts or blowers gave incomplete information on the acoustic performance of the whole system. Worse still, it had been found that it could be misleading to decide on which sub-system to improve, based solely on the sounds it generated.
“We initially used PowerFlow and PowerAcoustics FIND for the BMW 7 Series and Rolls-Royce Phantom,” says BMW’s group leader for overall vehicle development, Dr Michael Spickenreuther. “We were so impressed with the noise sourcing capability that we have now implemented FIND across all our platforms.”
By using PowerFlow’s transient simulation as the basis for an analysis of the complete HVAC system, BMW engineers were able to see how the sound was not only generated, but propagated through the system, from the initial source to the passenger’s ear. The new FIND model provided enhanced insight by localizing, quantifying and ranking the generated acoustic power, providing a more complex and accurate view on where noise reduction improvements could be made within the system.
BMW published this work in a research paper entitled, Acoustic source detection for climate systems via computational fluid dynamics for improved cabin comfort.
December 16, 2015
