Aeroacoustic Analysis of a NACA Duct

Regular paper

Nicolas Pignier

KTH Royal Institute of Technology

Wednesday 3 june, 2015, 09:00 - 09:20

0.1 London (90)

Since they were developed in the 1940s, NACA ducts have been used on numerous types of ground and air vehicles. Their particular shape allows for air to be passively dragged inside the vehicle with high pressure recovery and low drag. Although their aerodynamic properties have been extensively studied, little work has been done to assess their acoustic properties. In this paper an aeroacoustic analysis of a typical NACA duct is performed for low Mach numbers. The unsteady flow is solved through DES and the acoustics in the far field is computed through the use of a Ffowcs Williams-Hawkings (FW-H) integral. The results are analysed for various flow speeds. Acoustic results are presented for both permeable and impermeable FW-H surfaces. These results will be compared to experimental measurements. The mechanisms responsible for noise generation are discussed and some ideas for solutions to reduce the noise are proposed. Excessive noise generated by NACA ducts has been observed on trains where the inlets, usually located along the side walls of the power car, have been connected to tonal noise measured in pass-by tests. These observations will be discussed with regard to the simulation cases.

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