Broadband noise is generated by flow turbulence. This conversion process from turbulence to acoustic energy is particularly strong when the turbulent flow interacts with solid surface such as the wing leading or trailing edge. Scale-resolving simulations required to resolve the noise generating turbulent fluctuations are often computationally prohibitive, especially for high Reynolds number wall-bounded flows. The Fast Random Particle Mesh (FRPM) method predicts broadband noise by generating synthetic turbulent velocity fields based on the turbulence kinetic energy and dissipation rate modeled by the Reynolds-Averaged Navier-Stokes (RANS) equations, thus circumventing the often-exorbitant computational cost of scale-resolving simulations otherwise required to capture broadband noise sources. In FRPM, spatiotemporal white-noise is spatially convolved with user-defined filter kernels, enabling the reproduction of two-point turbulence statistics, compared to other stochastic techniques that primarily fit turbulence power spectra directly through random Fourier modes. The solenoidal nature of the fluctuations generated by FRPM helps avoid the creation of spurious sound sources. The broadband noise source synthesized by FRPM is propagated and interact with the solid surface by solving a pressure-Poisson equation.
The baseline FRPM model implemented in this work is enhanced using field-inversion machine learning (FIML), where an adjoint-based framework was developed to calibrate the FRPM model parameters in an optimal sense by minimizing the discrepancy between FRPM and high-fidelity reference solutions. The FIML-enhanced FRPM model is demonstrated with strongly improved predictive accuracy, capable of recovering noise-generating turbulence statistics compared to scale-resolving simulations.
This work has been conducted in close collaboration with Dr. Roland Ewert’s team at the German Aerospace Center (DLR).
Our group have developed a mid-fidelity GPU-accelerated aerodynamic-aeroacoustic simulation suite which balances the ability to capture the complex interactional flow physics and the time-to-solution requirement. The aerodynamic part of this solver consists of a non-linear vortex lattice method (NVLM) coupled with a random vortex particle method (RVPM). The RVPM approach generates a synthetic vorticity field for a specified energy spectrum, represented numerically as a collection of Lagrangian particles, which convect with the flow. The stochastic evolution of synthetic inhomogeneous and anisotropic turbulence is simulated according to a Langevin model. This provides an efficient means to predict leading-edge broadband noise due to interaction of turbulence with 3D bodies such as rotor turbulence ingestion noise and fan-OGV noise.