Competing Broadband Noise Mechanisms in Low-Speed Axial Fans

This paper compares two broadband noise mechanisms, the trailing-edge noise or self-noise, and the leading-edge noise or turbulence-ingestion noise, in several blade technologies. Two previously developed analytical models for these broadband contributions are first validated with well-defined measurements on several airfoils embedded in an homogeneous flow at low-Mach number. Each instrumented airfoil is placed at the exit of an open jet anechoic wind tunnel with or without a grid generating turbulence upstream of it. Sound is measured in the far field at the same time as the wall-pressure fluctuations statistics close to the airfoil trailing edge and the inlet velocity fluctuation statistics impacting the airfoil leading edge. The models are then compared in some practical cases representative of airframes, wind turbines, and automotive engine cooling modules. The airfoil models of the two mechanisms are then extended to a full rotating machine in open space. The model predictions of both mechanisms are compared with in-flight helicopter measurements and automotive engine cooling modules measurements. In both instances, the turbulence-ingestion noise is found to be a dominant source over most of the frequency range. The self-noise only becomes a significant contributor at high angles of attack close to flow separation.

[1]  S. E. Wright,et al.  The acoustic spectrum of axial flow machines , 1975 .

[2]  S. Moreau,et al.  Trailing Edge Noise Measurements and Prediction for Subsonic Loaded Fan Blades , 2002 .

[3]  Michel Roger,et al.  AERODYNAMIC NOISE OF A TWO-DIMENSIONAL WING WITH HIGH-LIFT DEVICES. , 1998 .

[4]  H. Arbey,et al.  Noise generated by airfoil profiles placed in a uniform laminar flow , 1983, Journal of Fluid Mechanics.

[5]  Meng Wang,et al.  Analysis of Flow Conditions in Freejet Experiments for Studying Airfoil Self-Noise , 2003 .

[6]  Sophie Pérennès,et al.  Caractérisation des sources de bruit aérodynamique à basses fréquences de dispositifs hypersustentateurs , 1999 .

[7]  R. Amiet.  Acoustic radiation from an airfoil in a turbulent stream , 1975 .

[8]  P. Moin,et al.  Computation of Trailing-Edge Flow and Noise Using Large-Eddy Simulation , 2000 .

[9]  W. Willmarth,et al.  Resolution and structure of the wall pressure field beneath a turbulent boundary layer , 1965, Journal of Fluid Mechanics.

[10]  Mårten Landahl.  Unsteady Transonic Flow , 1989 .

[11]  Martin V. Masek Fink,et al.  Experimental Evaluation of Theories for Trailing Edge and Incidence Fluctuation Noise , 1975 .

[12]  Michel Roger,et al.  Broadband fan noise prediction using single-airfoil theory , 2006 .

[13]  Stephane Caro,et al.  Aeroacoustic modelling of low pressure axial flow fans , 2000 .

[14]  R. K. Amiet,et al.  Acoustic radiation and surface pressure characteristics of an airfoil due to incident turbulence , 1976 .

[15]  R. K. Amiet,et al.  Noise of a model helicopter rotor due to ingestion of turbulence , 1979 .

[16]  Thomas J. R. Hughes,et al.  Computation of trailing-edge noise due to turbulent flow over an airfoil , 2004 .

[17]  R. Amiet.  Noise due to turbulent flow past a trailing edge , 1976 .

[18]  T. Brooks,et al.  Trailing edge noise prediction from measured surface pressures , 1981 .

[19]  Harvey H. Hubbard,et al.  Aeroacoustics of large wind turbines , 1991 .

[20]  Damiano Casalino,et al.  Prediction of Rod-Airfoil Interaction Noise Using the Ffowcs-Williams-Hawkings Analogy , 2003 .

[21]  W. Blake,et al.  A Statistical Description of Pressure and Velocity Fields at the Trailing Edges of a Flat Strut , 1975 .

[22]  R. H. Schlinker,et al.  Helicopter rotor trailing edge noise , 1981 .

[23]  J. L. Adamczyk.  The passage of an infinite swept airfoil through an oblique gust. [approximate solution for aerodynamic response , 1974 .

[24]  Michel Roger,et al.  Effect of Angle of Attack and Airfoil Shape on Turbulence-Interaction Noise , 2005 .

[25]  Michel Roger,et al.  Back-scattering correction and further extensions of amiet's trailing-edge noise model. Part 1: theory , 2005 .

[26]  S. Moreau,et al.  Effect of Airfoil Aerodynamic Loading on Trailing Edge Noise Sources , 2005 .

[27]  M. S. Howe.  A review of the theory of trailing edge noise , 1978 .

[28]  Thomas F. Brooks,et al.  Airfoil self-noise and prediction , 1989 .

[29]  Michel Roger,et al.  Broadband Self Noise from Loaded Fan Blades , 2004 .

[30]  J. Williams,et al.  Aerodynamic sound generation by turbulent flow in the vicinity of a scattering half plane , 1970, Journal of Fluid Mechanics.

[31]  S. B. Khelil,et al.  Numerical prediction of the unsteady flow and radiated noise from a 3D lifting airfoil , 2001 .

[32]  R. K. Amiet,et al.  Effect of the incident surface pressure field on noise due to turbulent flow past a trailing edge , 1978 .