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A novel method for efficient and accurate jet noise prediction is developed and tested in the framework of coupled LES and stochastic noise modeling. In the proposed method, the low frequency range of the acoustic spectrum, which corresponds to large turbulent structures, is resolved with an implicit LES model by employing higher-order spatial and temporal discretizations. The high frequency range, which corresponds to the fine-scale turbulence, is modeled via a stochastic broadband noise generation model. The inputs to the stochastic model are represented by statistics from an axisymmetric RANS jet simulation. The smaller synthetic scales are convected by larger scales, accounting for the effects of sweeping from the larger LES-resolved turbulent scales. The farfield acoustic data is obtained using either the Linearized Euler Equations, or an acoustic analogy based on the Ffowcs-Williams Hawkings method. The method is evaluated on cold and heated jets at different Reynolds numbers.

In this study, a hybrid approach for non-linear jet noise predictions in complex environments is presented and validated. The method differs from traditional approaches in that interactions of the jet with the surrounding structures as well as non-linear disturbances propagating over large distances are taken into consideration in order to quantify their effects on sound generation and propagation. The noise sources founded in the jet plume and the near-field are first computed using the full Navier-Stokes equations. The variables of interest are then interpolated into a second domain. After penalized, they are used as source terms in the non-linear Euler equations to calculate the sound propagation. The interpolation and penalization steps are performed using a buffer region designed by the principles of sponge layers. The effective one-way communication between the two domains and the capabilities of the buffer region to transfer the data from the NS to the Euler domain without any loss of detail is demonstrated. Results from two- and three-dimensional jets both in free space and interacting with solid obstacles are presented. Comparisons with DNC and experimental data in terms of sound pressure level spectra are in good agreement with the ones calculated by our method.