In the present paper, the attention is focused on the effect of local porous material on aerodynamic sound radiated from two-dimensional airfoil. We measured the aerodynamic sound radiated from the airfoil with porous material, tripping wire and porous plate which are mounted locally on the surface of the airfoils near the leading edge. At the normal airfoil, discrete frequency noise is clearly observed at small attack angle. However, it is clear that its noise generated from the airfoil decreased with the local porous material on the surface of pressure side of the airfoil. The porous material is effective to reduce this noise compared with the others. And the sound absorbing coefficient and the air permeability were measured for test porous material. The sound absorbing coefficient increased at the high frequency band, and the air permeability became small for porous materials. As the attack angle increased, the discrete frequency noise was not generated from the normal airfoil. The broadband noises were almost same for all test airfoils.
Cite this paper
H. Hamakawa, K. Hosokai, T. Adachi and E. Kurihara, "Aerodynamic Sound Radiated from Two-Dimensional Airfoil with Local Porous Material," Open Journal of Fluid Dynamics, Vol. 3 No. 2, 2013, pp. 55-60. doi: 10.4236/ojfd.2013.32A009.
 T. Fukano, A. A. Talukuder, T. Kozu and Y. Takamatsu, “Discrete Frequency Noise Generated from a Flat Plate in Parallel with a Uniform Oncoming Flow,” Memoirs of the Faculty of Engineering, Kyushu University, Fukuoka, 1984, pp. 19-39.
 R. E. Longhouse, “Control of Tip-Vortex Noise of Axial Flow Fans by Rotating Shrouds,” Journal of Sound and Vibration, Vol. 58, No. 2, 1978, pp. 201-214.
 T. Fukano, Y. Takamatsu and Y. Kodama, “The Effects of Tip Clearance on the Noise of Low Pressure Axial and Mixed Flow Fans,” Journal of Sound and Vibration, Vol. 105, No. 2, 1986, pp. 291-308.
 R. W. Paterson, P. Vogt, M. Fink and C. Munch, “Vortex Noise of Isolated Airfoils,” Journal of Aircraft, Vol. 10, No. 5, 1973, pp. 296-302. doi:10.2514/3.60229
 C. K. W. Tam, “Discrete Tones of Isolated Airfoils,” Journal of the Acoustical Society of America, Vol. 55, No. 6, 1974, pp. 1173-1177. doi:10.1121/1.1914682
 R. E. Longhouse, “Vortex Shedding Noise of Low Tip Speed, Axial Flow Fans,” Journal of Sound and Vibration, Vol. 53, No. 1, 1977, pp. 25-46.
 M. R. Fink, “Prediction of Airfoil Tone Frequencies,” Journal of Aircraft, Vol. 12, No. 2, 1975, pp. 118-120.
 H. Arbey and J. Bataille, “Noise Generated by Airfoil Profiles Placed in a Uniform Laminar Flow,” Journal of Fluid Mechanics, Vol. 134, 1983, pp. 33-47.
 S. Nakashima and S. Akishita, “Discrete Tone Noise on Two-Dimensional Wing (Numerical Analysis on Boundary Layer Instability on Wing),” Transactions of JSME, Vol. 66, No. 648B, 2000, pp. 2056-2064.
 S. Takagi and Y. Konishi, “Frequency Selection Mechanism of Airfoil Trailing-Edge Noise,” Journal of Aircraft, Vol. 47, No. 4, 2010, pp. 1111-1116.
 T. Fukano, Y. Kodama and Y. Takamatsu, “Prediction of Sound Pressure Level radiated from Low Pressure Axial Flow Fan and Mixed Flow Fan,” Transactions of JSME, Vol. 51, No. 466, 1985, pp. 1825-1832.
 C. Polacsek, G. Reboul, V. Clair, T. Le Garrec and H. Deniau, “Turbulence-Airfoil Interaction Noise Reduction using Wavy Leading Edge: An Experimental and Numerical Study,” Proceedings of Inter-Noise 2011, Osaka, 4-7 September 2011, 11 pp.
 M. Nishimura, T. Goto and T. Ito, “Study on Reducing Noise from a Small Axial Cooling Fan by Using Pile-Fabrics,” Proceedings of Internoise 2006, Honolulu, 3-6 December 2006, 9 pp.
 S. Akishita, “Grazing Effect of Surface Impedance for Perforated Surface with Very Small Diameter,” Proceedings of Inter-Noise 2007, Istanbul, 28-31 August 2007, pp. 1762-1769.
 T. Sueki, T. Takaishi and M. Ikeda, “Application of Porous Material to Reduce Aerodynamic Noise Caused by a Pantograph,” JSME Annual Meeting 2007, No. 7-1, 2007, pp.71-72.
 H. Hamakawa, K. Nakashima and H. Matsue, “Reduction of Noise Generated from Small Wind Tunnel,” Proceedings of the Second Asian Joint Workshop on Thermophysics and Fluid Science, Luoyang, 12-14 May 2008, pp. 122-126.