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Dynamics >>23
Flow-induced
noise prediction
Zoubida
El Hachemi, LMS International, Belgium
Aerodynamic noise is becoming a big concern in modern industry. The reduction of other primary noise sources (such as structure borne noise) has left aerodynamic noise as one of the most significant sources of noise pollution in modern industrial design. In the highly competitive automotive industry, the reduction of both internal and external aerodynamic noise is critical, as ever more discerning customers demand a quieter more comfortable driving environment. The control aerodynamic noise is also a principal concern in industries as diverse as aerospace, process, electronics and home appliance. Being able to model accurately the location aeroacoustic sources and propagation of generated noise is therefore crucial for the engineers tasked with reducing extraneous noise.
Predicting flow-induced noise requires modeling both of the turbulent flow and the acoustics, which for industrial applications cannot easily be done using direct methods. A pragmatic approach is based on the aeroacoustic analogies (Lighthill, Ffowcs-Williams) and consists of first solving the flow equations and deriving equivalent aero-acoustic noise sources from the generated flowfield. This approach enables real-life problems to be tackled with a reasonable cost and a good accuracy.
Based on these aero-acoustic analogies, LMS International, the world leading software provider for vibro-acoustic simulations, has developed a unique solution to simulate flow-induced noise and aeroacoustic phenomena long before the physical prototype stage. The solution is embedded in LMS SYSNOISE and uses STAR-CD results to create aeroacoustic sources from which it is able to predict the radiation, scattering and transmission of sound waves and the structural vibrations induced by fluids.
The SYSNOISE aeroacoustic module calculates flow-induced noise, using the results of Computational Fluid Dynamics through a direct coupling with STAR-CD. The simulation process starts with solving the flow equations using STAR-CD. Next, the CFD data is passed to SYSNOISE, through a dedicated interface, and processed to define sets of equivalent sources characterizing the aero-acoustic noise. Finally, SYSNOISE computes the radiated and/or scattered noise using its regular BEM (Boundary Element Method) or FEM (Finite Element Method) acoustic solvers, giving results at the surfaces and at any point in the field. The powerful post-processing capabilities of LMS SYSNOISE further deliver the necessary insight in the acoustic behavior of the design.
LMS SYSNOISE not only features a very efficient data transfer from STAR-CD, but also handles incompatibilities between the CFD and acoustic meshes easily. It automatically transforms time data into the frequency domain, maps the CFD data from the CFD mesh on the acoustic mesh, and finally generates the required aero-acoustic sources. These can be dipole-like, quadrupole-like or “rotating” dipole-like, enabling acoustic engineers to model and predict flow noise from stationary surfaces such as mirrors, as well as noise from rotating surfaces such as HVAC blowers and computer fans.
STAR-CD/SYSNOISE coupled technology has been used for many diverse applications and the results of the coupled approach have been presented at several prestigious conferences. A joint paper involving Denso thermal Systems Italy, CD-adapco and LMS International is published at the Fan noise conference 2003 (“Investigation of the tonal noise radiated by subsonic fans using the aeroacoustic analogy”). The paper investigates the tonal noise radiated by a subsonic blower fan of an HVAC system. Comparison of the numerical results with the test showed very good agreement.
Conclusion
Flow-induced noise prediction is one of the most difficult challenges faced by engineers today. Direct approaches are not capable of treating such problems. Thanks to a one way coupling of STAR-CD’s best of class CFD methodologies with SYSNOISE’s state of the art acoustic technologies, STAR-CD and LMS SYSNOISE offer coupled breakthrough capabilities for flow-induced noise prediction in industrial applications.
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