Numerical Study of Self-Noise Produced by an Airfoil with Trailing-Edge Serrations

Abstract

The main objective of the present work is to investigate the mechanism of trailing-edge airfoil noise. The vorticity associated with the unsteady turbulent structures is scattered by the trailing edge and acoustic waves are generated. It has been recognized that trailing-edge noise can be reduced by introducing sharp sawtooth serrations at the trailing-edge. The flow past a serrated airfoil, with free-stream Reynolds number 6.0 × 10 5 and Mach number M = 0.17, is studied. A compressible Large Eddy Simulation is used for computing the near field, and the far-field acoustic propagation is obtained applying the integral formulation of Ffowcs Williams and Hawkings. The results of the serrated configurations, and its baseline geometry, are compared with the experimental data obtained by ISVR in the frame of the European Project FLOCON. It is shown that the structure of the flow field near the trailing edge is strongly affected by the presence of the serrations. The integral scale lengths of the flow structures in the wake near the trailing edge, are much smaller than in the baseline case. The OASPL directivities of the acoustic far-field are in good agreement with the experimental data, and the serrated airfoil presents a reduction of acoustic PSD in the low and mid frequency ranges, with a reduction ranging from ∼ 10 dB at low frequencies, to ∼ 5 dB in the mid range. For higher frequencies, the PSD levels of the serrated airfoil become comparable (f ≈ 4000 Hz) and then are higher with respect to the baseline spectrum.

Flow topology and acoustic emissions of trailing edge serrations at incidence

“…Similar flow behavior, with a transverse motion between the teeth toward the suction side, has been reported by Arina et al (2012).…”

Experimental and numerical study on noise reduction mechanisms of the airfoil with serrated trailing edge

“…In order to control the grid number, the spanwise length of the computational domain is 2λ = 0.012 m = 0.08c. The spanwise length used here is larger than Winkler 28 and Arina et al 29 used in their studies and the simulation results of this study proved it was sufficient for simulating spanwise vortices. The details of the grid setting are shown in Fig.…”

Boundary layer characterization and acoustic measurements of flow-aligned trailing edge serrations

“…Nevertheless, while numerical studies such as those of Jones et al (2010), Sandberg and Jones (2011), Jones and Sandberg (2012) and Arina et al (2012) have provided field velocity and pressure solutions, as well as unsteady surface pressure information, obtaining the latter experimentally over serrations is difficult due to the relatively large physical size of available transducers with respect to the surface pressure structures, and to the physical thickness of the serrations themselves.…”