NEW CPV-RESULTS OF NACA 0012 TRAILING-EDGE NOISE

Introduction Quantitative measurement of Turbulent Boundary-Layer Trailing-Edge (TBL-TE) noise in a non-aeroacoustic facility is a delicate task, as the airfoil self noise has to be separated from the typically higher background noise. At the Institute of Aerodynami cs and Gas Dynamics (IAG) the Coherent Particle Velocity (CPV) method was developed [1] for tw -dimensional airfoil trailing edge (TE) noise measurements in wind tunnels with high aerodynamic qua l ty, which however often show high background noise levels. It is therefore specifica lly suited for aeroacoustic validation of low-noise airfoil sections under well defined aerodynamic boundary condit ions. Cross-correlation of two hot-wire signals is used to measure the Co rent Particle Velocity of the sound waves. The setup can be compared to the Coherent Output Power (C OP) method developed by Hutcheson and Brooks [2]. First CPV experiments were performed on a symmetric 4.2% thi ck ’flat plate like’ airfoil (c = 0.5 m) at zero angle of attack. This represents some benchmark case due to the low noise emission in comparison to practical airfoil sections. Subsequently the CPV-me thod was successfully applied for the validation of cambered wind turbine airfoils in the SIROCC [3] project. In addition comparisons of CPV results to phased acoustic array measurements showed good agreem ent [4,5]. CPV-measurements on NACA 0012 airfoil sections have been performed [6] with the intent to validate absolute sound pressure levels in comparison to published results [7, 8]. The present paper concentrates on analysis of proven scaling laws applied to the measured data in or der to btain more insight into the ranges of applicability of the CPV method. In addi tion a background noise (BGN) correction scheme is proposed, extending the range of valid data to lower frequenc i s.