In this work a hybrid RANS/CAA methodology is used to predict trailing-edge noise of a controlled-diffusion airfoil. A time domain stochastic solver based on the Random Particle Mesh method introduced by Ewert et al. is used to generate turbulent fluctuations in 2-D that accurately reproduce statistical and mean-flow features provided by steady RANS. Acoustic Perturbation Equations coupled with the stochastic solver are solved in time domain, using a vortex sound source term defined in terms of stochastically generated turbulent velocity fluctuations. The far-field sound pressure level obtained using Kirchhoff extrapolation method followed by 2-D to 3-D correction taking into account the finite span of the airfoil is compared with the available experimental data. The numerical results are found to be in good agreement for the frequencies for which experimental data is available. The results indicate the suitability of the 2-D RANS/CAA approach for trailing-edge noise prediction from airfoils with uniform cross-section in the spanwise direction.

A numerical approach to predict broadband trailing-edge noise for low Mach number flows is presented. It is based on the combination of a Helmholtz solver to propagate sound waves with a sound source term computed stochastically. The sound propagation is performed in the frequency domain using a high-order finite element solver. The stochastic approach is based on a Random Particle-Mesh method. The performance of this numerical approach is first examined for a Gaussian source. The numerical approach is then applied to a NACA0012 airfoil for flow Mach numbers of 0.11 and 0.16 and to a controlled-diffusion airfoil for a Mach number of 0.047. The predicted sound levels are compared with experimental data and acoustic results obtained from the Acoustic Perturbations Equations. The mean flow does not significantly modify the acoustic propagation. Using a no-flow propagation model like the Helmholtz equation is therefore a valid approach for low Mach numbers. The reduced computational cost of a Helmholtz calculation, together with the speed of the RPM turbulence synthesis, allows for fast predictions. While this approach provides relative assessments between different configurations (in particular the spectrum shape), it often requires the inclusion of calibration factors determined from reference measurement or numerical data.

In this study, a computational aeroacoustic strategy is presented for the prediction of airfoil trailing-edge noise. This strategy is based on the use of a random particle-mesh method to compute noise sources, and the use of a Helmholtz solver to propagate sound waves. The random particle-mesh method is a stochastic approach that reconstructs sound sources from the steady mean flow statistics provided by an incompressible Reynolds-averaged Navier-Stokes simulation. The sound propagation is carried out in the frequency domain using a high-order finite element solver. For low-Mach number flows, assuming negligible mean flow convection effects, a non-homogeneous Helmholtz equation with a source term provided by the random particle-mesh method is solved. The performance of the numerical strategy is evaluated by simulating the sound radiated from the trailing-edge of a controlled-diffusion airfoil. The flow around the airfoil is characterized by a Mach number of 0.047 and a Reynolds number based on the airfoil chord length of Re c = 1.6 × 10 5 . The frequency domain results are found to be in good agreement with experimental data from the literature and with a full time-domain computation, used as reference. In particular, the trailing-edge noise radiated in the far-field region is well predicted.