Effects of fluid-structure interaction on the trailing-edge noise

In the present study, the effects of fluid-structure interaction (FSI) on the trailingedge noise are numerically investigated, particularly for the cases of wake instability and Karman vortex shedding. The trailing-edge is modelled as a flat plate with an elastic cantilever end and its flow-induced vibration is solved by an eigenmode analysis with the Galerkin method. The FSI analysis is conducted in a fully coupled manner with direct numerical simulation (DNS) of the flow and sound. Computed solutions for the wake instability show that when the first-eigenmode natural frequency (?n) of the cantilever is close to be resonant with the wake characteristic frequency (?c), the sound pressure level (SPL) is significantly reduced by -20 dB or increased by +15 dB, depending on the ratio of ?n/?c. For Karman vortex shedding, the flow and acoustic details are somewhat different but FSI also has considerable impacts on the SPL and directivity, if ?n is close to ?c

Numerical investigation of the aerodynamic noise from a forward-facing step

In the present study, aerodynamic noise from a forward-facing step is numerically investigated for Reynolds number based on the step height, Reh=8,000 and flow Mach number, M=0.03. A three-dimensional flow over the forward-facing step is calculated by the incompressible large eddy simulation (LES), while its acoustic field is solved by the linearized compressible perturbed equations (LPCE). The space-time characteristics of the surface pressure over the step and the flow strucuture low-dimensionalized by a filtered proper orthogonal decomposition (POD) method indicate two different noise generation mechanisms at St=0.1 & 0.4~0.8. The low frequency noise is generated by a flapping motion of the shear layer. The high frequency noise is, however, generated by the breaking-off of the shear layer, due to the Kelvin-Helmholtz instability. A dominant noise source for the forward-facing step with an extended span will be expected to be around the step-corner (step front-face and leading-edge over the step) rather than near the shear layer reattachment point because the spanwise coherence length for the shear layer flapping mode is much longer than that for the shear layer breaking-off mode

Computation of aerodynamic noise for rod wake-airfoil interactions

Aerodynamic noise from the rod wake-airfoil interactions at M=0.2 and Re_D=46,000 is computed by solving the linearized perturbed compressible equations (LPCE), with the acoustic source and hydrodynamic flow variables computed from the incompressible LES. A 2D LPCE calculation is conducted at zero spanwise wave-number (k_z=0) with an assumption of statistical homogeneity in the spanwise direction. Then, a 2D Kirchhoff method is used to extrapolate the sound field at the acoustic far-field boundary (40D) up to the microphone location (185D away from the airfoil chord center). Finally, a power spectrum density (PSD) for actual span (30D) is predicted by Oberais correction method for 3D spectral acoustic pressure and spanwise coherence function for the wall pressure. The computational results for flow and acoustics are critically validated with the experimental data measured at the Ecole Centrale de Lyon