Experimental investigation of trailing edge noise by measuring unsteady surface pressures

Requirement of reducing undesirable noise from airplanes, wind turbines blades and fans resulted in the identification of noise sources of such equipment in many research works. Turbulent boundary layer trailing edge (T.E.) noise is one of the main sources of aerodynamic noise and extensive studies have been conducted on it during the past decades. Previous studies have shown that surface pressure spectra, the spanwise length scale of the SPFs and eddy convection velocity in the T.E. region are crucial quantities in determination of the far-field trailing edge noise. In the present study, for measuring these parameters and hence predicting the far-field trailing edge noise, a flat-plate model is designed and built. The flat plate is equipped with several streamwise and spanwise miniature condenser microphones, FG-23329-P07, acting as surface pressure transducers. All the experiments were carried out in a subsonic wind tunnel for three free-stream velocities: 10, 15 and 20 m/s. The spanwise length scale and eddy convection velocity are calculated by simultaneously measuring of unsteady surface pressure respectively in both streamwise and spanwise directions and using cross spectral density. The experimental results, including the surface pressure spectra, longitudinal and lateral coherence and eddy convection velocity provide many information about the flow field structure in the turbulent boundary layer. The results also show that the best collapses in the surface pressure spectra at low frequency and middle to high frequencies can be obtained by using outer and inner layer scales respectively. Furthermore, the longitudinal and lateral coherences can provide adequate information about the lifespan (or, inversely, the decay) of the eddies and their physical size. Finally, the trailing edge noise from flat plate has been predicted by using the analytical Amit-Roger model and results show the effectiveness of this model for prediction of far-field turbulent boundary layer trailing edge noise.