ROTATING MACHINERY NOISE -...
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AEROACOUSTICS A QUIET REVOLUTION Low speed rotating machinery is found in a variety of applications such as ground transportation engine cooling, electronic cooling, ventilation systems, wind-turbines and power generators. Due to the growing importance of acoustic comfort in these competitive markets, flow-induced noise problems related to rotating geometry should be addressed as early as possible during the development process in order to avoid expensive countermeasures and make sure that noise targets are achieved. Fans are most often evaluated in stand-alone configurations, although practical integration into complex systems or sub-systems often results in an unpredictable increase of noise levels. As building full-scale physical prototypes is often prohibitively expensive, fan noise control engineers are typically limited to balance between a trial-and-error test approach and expertise gained through the years. However, they lack a robust and accurate way to estimate the noise early in the development process, and the ability to explore simulation-driven design strategies based on noise sources identification. TECHNICAL CHALLENGES Experimental assessment of acoustic performance of fans and other rotating objects has severe limitations due to the difficulty of physical testing or equipment size. As an alternative to experimental methods, numerical approaches are more and more commonly introduced into the development process. The physical mechanisms (related to flow-induced noise from rotating machinery) are however varied and complex. It is a key challenge for Computational Aero-Acoustics (CAA) methods to capture simultaneously: • Noise generation - a transient phenomenon by definition, traditional CFD codes typically have difficulty accurately predicting transient effects in reasonable timeframes. The complex interaction of rotating blades with nearby stationary geometry is a primary source of noise, and the typical moving reference frame (MRF) technique fails to capture this effect. • Tonal noise - associated with the quality of the incoming flow, rotor-casing interactions, rotating stall conditions and unsteadiness of the flow field. • Broadband noise - acoustic content related to vortex shedding, flow detachments, turbulent boundary noise and tip vortex noise. • Installation effects - affecting the inlet flow conditions and the acoustic re- sponse of the system. • Small acoustic pressure waves - generated by turbulent flow structures radiated outside the convective region ROTATING MACHINERY NOISE ©2016 Exa Corporation. All rights reserved. For more information please visit www.exa.com. Alternator noise: the high speed rotation of the internal rotor blades induces flow structures and tonal noise sources that must be mitigated before production. Automotive axial cooling fan: acoustic pressure field (left) and instantaneous flow (right) captured during the same transient and compressible simulation; see reference [6] on back.
Transcript of ROTATING MACHINERY NOISE -...
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S A QUIET REVOLUTIONLow speed rotating machinery is found in a variety of applications such as ground transportation engine cooling, electronic cooling, ventilation systems, wind-turbines and power generators. Due to the growing importance of acoustic comfort in these competitive markets, flow-induced noise problems related to rotating geometry should be addressed as early as possible during the development process in order to avoid expensive countermeasures and make sure that noise targets are achieved. Fans are most often evaluated in stand-alone configurations, although practical integration into complex systems or sub-systems often results in an unpredictable increase of noise levels. As building full-scale physical prototypes is often prohibitively expensive, fan noise control engineers are typically limited to balance between a trial-and-error test approach and expertise gained through the years. However, they lack a robust and accurate way to estimate the noise early in the development process, and the ability to explore simulation-driven design strategies based on noise sources identification.
TECHNICAL CHALLENGES
Experimental assessment of acoustic performance of fans and other rotating objects has severe limitations due to the difficulty of physical testing or equipment size. As an alternative to experimental methods, numerical approaches are more and more commonly introduced into the development process. The physical mechanisms (related to flow-induced noise from rotating machinery) are however varied and complex. It is a key challenge for Computational Aero-Acoustics (CAA) methods to capture simultaneously:
• Noise generation - a transient phenomenon by definition, traditional CFD codes typically have difficulty accurately predicting transient effects in reasonable timeframes. The complex interaction of rotating blades with nearby stationary geometry is a primary source of noise, and the typical moving reference frame (MRF) technique fails to capture this effect.
• Tonal noise - associated with the quality of the incoming flow, rotor-casing interactions, rotating stall conditions and unsteadiness of the flow field.
• Broadband noise - acoustic content related to vortex shedding, flow detachments, turbulent boundary noise and tip vortex noise.
• Installation effects - affecting the inlet flow conditions and the acoustic re- sponse of the system.
• Small acoustic pressure waves - generated by turbulent flow structures radiated outside the convective region
ROTATING MACHINERY NOISE
©2016 Exa Corporation. All rights reserved. For more information please visit www.exa.com.
Alternator noise: the high speed rotation of the internal rotor blades induces flow structures and tonal noise sources that must be mitigated before production.
Automotive axial cooling fan: acoustic pressure field (left) and instantaneous flow (right) captured during the same transient and compressible simulation; see reference [6] on back.
EXA SOLUTIONExa® provides a complete Computational Aero-Acoustics (CAA) solution through PowerFLOW® with rotating geometry capability and PowerACOUSTICS®
• PowerFLOW’s inherently transient solution accurately predicts the complex time dependent turbulent flow structures and the resulting noise sources induced by the rotating objects.
• PowerFLOW’s true rotating geometry capability provides time accurate simulation of rotation and captures all types of interactions more precisely than traditional Moving Reference Frame (MRF) methods.
• PowerFLOW’s inherently compressible solution predicts the radiated noise simultaneously with the flow induced noise sources.
• PowerFLOW can handle fully detailed geometry and capture all the interactions between the fan and the surrounding components.
• For applications requiring prediction of noise propagation to the far field (community noise), such as windturbines and heavy equipment pass-by fan noise, PowerFLOW transient results can be coupled to the PowerACOUSTICS Far Field Noise module, which uses an acoustic analogy method based on the Ffowcs-Williams Hawkings equation.
• Easy-to-use analysis and visualization capabilities with PowerACOUSTICS and Power- VIZ® provide insight into sources of noise. Band-filtered pressure analyses can be used to isolate phenomena at specific frequency bands of interest and for example determine the origin of the blade passing frequency noise. Flow Induced Noise Detection (FIND) module unique flow noise source detection capability provide engineers with the tools they need to identify design features responsible for noise generation for an efficient simulation-driven design process.
ROTATING MACHINERY NOISECONTACT INFO
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SELECTED REFERENCES:1. V. Le Goff, V. Vidal, M. Fakes, P. Chiozzi, E. Le Goff,
F. Pérot, M.S. Kim, Flow-induced noise predictions of an automotive alternator using LBM, TurboExpo 2014, Düsseldorf, Germany, June 16th -20th , 2014
2. K. Norisada, M. Sakai, S. Ishiguro, M. Kawaguchi, F. Pérot, K. Wada, HVAC Blower Aeroacoustic Predictions, SAE 2013 World Congress & Exhibition, Detroit, MI, April 16th-18th, 2013.
3. F. Pérot, A. Mann, D. Casalino, M.S. Kim, E. Fares, Advanced Noise Control Fan Direct Aeroacoustics Predictions using LBM, to be published at the 18th AIAA/CEAS Conference, Colorado Springs, CO, USA, June 4th -9th , 2012
4. F. Pérot, M.S Kim, V. Le Goff, X. Carniel, Y. Goth, C. Chassaignon, Numerical optimization of the noise reduction of a radial fan using flow obstructions, Fan2012 International Conference, April 2012, Senlis, France
5. M.S. Kim, F. Pérot, M. Meskine, Aerodynamics and acoustics predictions of the 2-blade NREL wind turbine using a Lattice Boltzmann Method, 14th ISROMAC, February 2012
6. F. Pérot, S. Moreau, M.S. Kim, M. Henner, D. Neal, Direct aeroacoustic prediction of a low-speed axial fan, AIAA paper 2010-3887, 14th AIAA/CEAS, Stockholm, June 2010.
CETIM Backward centrifugal fan instantaneous flow: the tonal noise induced by the periodic blade passage is controlled by a flow obstruction mounted in front of the fan. ref [4].
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