Effects of Geometric Parameters of Perforated Diffuser on Sound Pressure Level Sourced By Airflow

Abstract

This study investigates the aeroacoustic behaviors of a square truncated perforated diffuser under airflow, commonly used in Air Handling Units (AHUs). The design parameters are fundamentally taken into account to unveil the aeroacoustic performance of the diffuser. Initially, unsteady-state Computational Fluid Dynamics (CFD) simulations are conducted based on models that accurately represent the fluid domain of the chamber with the perforated diffuser in the ANSYS Fluent environment. Subsequently, the Ffowcs Williams and Hawkings (FW-H) method integrated into the software is employed to acquire time-dependent signals from microphones placed in three different locations within a perforated diffuser chamber. Finally, the results are converted to a frequency range of 0-1000 Hz using the Fast Fourier Transform (FFT) method, and the SPL values are obtained. The results show that the microphone location is crucially important to determine SPL and the porosity reduction from 0.55 to 0.35 can reduce SPL by approximately 30-40 dB. Variations in wall thickness of the diffuser fluctuated between 5-10 dB at each frequency value.

Keywords

• Air handling units
• Computational fluids dynamic
• Perforated diffuser
• Sound pressure level
• Ansys fluent

References

1. Bezci H. 2009. Aeroacoustic properties of a radial fan. PhD Thesis, İstanbul Technical University, Institute of Science and Technology, İstanbul, Türkiye, pp: 85.
2. Bulut S, Unveren M, Arisoy, A, Boke, Y. 2011. Reducing internal losses in air handling units with CFD analysis method. TMMOB X. National Plumbing Engineering Congress and Exhibition, April 11-13, İzmir, Türkiye, pp: 291-326.
3. Erdoğan A, Daşkın M. 2023. Comparing of CFD contours using image analysing method: A study on velocity distributions. BSJ Eng Sci, 6(4): 633-638.
4. Erdoğan A. 2017. Investigation of airflow in empty chambers with perforated diffuser designed for air handling units in terms of flow and acoustic. PhD Thesis, İnönü University, Institute of Science, Malatya, Türkiye, pp: 115.
5. Fluent A. 2009. 12.0 User’s guide. Ansys Inc, 6: 552.
6. Kaltenbacher M, Hüppe A, Reppenhagen A, Tautz M, Becker S, Kuehnel V. 2016. Computational aeroacoustics for HVAC systems utilizing a hybrid approach. SAE Int J Passeng Cars Mech, 9(3): 1047-1052.
7. Kamer MS, Erdoğan A, Taçgün E, Sonmez K, Kaya A, Aksoy IG, Canbazoglu S. 2018. A performance analysis on pressure loss and airflow diffusion in a chamber with perforated V-profile diffuser designed for air handling units (AHUs). J Appl Fluid Mech, 11: 1089-1100.
8. Kandekar A, Nagarhalli P, Dol Y, Thakur S, Gupta B, Jadhav T. 2019. HVAC system noise prediction through CFD simulation. SAE Tech Pap, 26: 210.

9. Martinez-Lera P, Hallez R, Bériot H, Schram, C. 2012. Computation of sound in a simplified HVAC duct based on aerodynamic pressure. 18th AIAA/CEAS Aeroacoustic Conference (33rd AIAA Aeroacoustic Conference), June 4-6, Colorado, US, pp: 1-10.
10. Mikedis K. 2023. Prediction of aerodynamically induced noise in automotive HVAC systems. Diploma Thesis, National Technical University, Athens School of Mechanical Engineering, Athens, Greece, pp: 93.
11. Morris PJ, Boluriaan S, Shieh CM. 2004. Numerical simulation of minor losses due to a sudden contraction and expansion in high amplitude acoustic resonators. Acta Acust United Acust, 90: 393-409.
12. Ueda Y, Biwa T, Mizutani U, Yazaki T. 2002. Acoustic field in a thermoacoustic Stirling engine having a looped tube and resonator. Appl Phys Lett, 81: 5252-5254.
13. Yapanmış BE. 2016. Design of perforated diffuser as a pre-silencer. PhD Thesis, Mersin University, Institute of Science, Mersin, Türkiye, pp: 95.
14. Yu Y, Woradechjumroen D, Yu, D. 2014. A review of fault detection and diagnosis methodologies on air-handling units. Energy Build, 82: 550-562.
15. Zoccola JP. 2004. Effect of opening obstructions on the flow-excited response of a Helmholtz resonator. J Fluids Struc, 19: 1005-1025.