A procedure to accurately simulate a free hot supersonic jet and its associated noise, which uses simultaneously a turbulence tripping method and a two-way coupling between a flow solver and a nonlinear acoustic solver, is proposed in this study. A Mach 3.1 overexpanded hot jet is computed via a large-eddy simulation by solving the filtered Navier-Stokes equations with a finite volume method on unstructured grids. The resulting noise is propagated in the far field by solving the full Euler equations with a high-order discontinuous Galerkin method on unstructured grids. The full convergent-divergent nozzle is explicitly included in the computational domain thanks to the unstructured flow solver. Both a refined grid and a geometrical boundary layer tripping in the convergent are used to get highly disturbed turbulent conditions at the nozzle lips. The flow field appears to agree with the expected turbulence behavior and the available experimental data. The jet development shows significant improvement compared to similar past simulations. The far field acoustic levels are finely recovered at most of observation angles. An analysis of the acoustic near and far fields is then performed. The studied conditions lead to strong shock-associated noise and Mach wave emission. The spatio-frequency and azimuthal content of the acoustic field is described in order to identify the main noise properties. A particular noise component, different from screech tones and radiating upstream like Mach waves, is highlighted. Nonlinear propagation effects are finally quantified through specific metrics. They are found significant in both the near and the far fields which justifies the use of a nonlinear acoustic solver.

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In this study, the methodology relying on LES for the generation of the acoustic sources coupled with an Euler solver for their propagation, previously developed for a free hot supersonic jet, has been applied to a similar jet but impinging on a plate with an exhaust hole. Attention has been paid to the turbulent state of the nozzle exit boundary layer, which is a key parameter for jet noise simulation.

A two-way coupling on unstructured meshes between a flow and a high-order acoustic solvers for jet noise prediction is considered. The flow simulation aims at generating acoustic sources in the near field while the acoustic simulation solves the full Euler equations, thanks to a discontinuous Galerkin method, in order to take into account nonlinear acoustic propagation effects. This methodology is firstly validated on academic cases involving nonlinear sound propagation, shock waves and convection of aerodynamic perturbations. The results are compared to analytical solutions and direct computations. A good behaviour of the coupling is found regarding the targeted space applications. An application on a launch pad model is then simulated to demonstrate the robustness and reliability of the present approach.

This study aims to numerically investigate the noise radiated by a reduced-scale rocket engine jet at lift-off conditions including a flame trench. An over-expanded Mach 3.1 hot jet entering a flame duct where it impinges on a deflector before being guided in a horizontal duct, is considered. The computation is performed with a two-way coupled approach on unstructured grids. This methodology relies on a large-eddy simulation of the jet and the acoustic near field, associated with a full Euler simulation of the acoustic far field. The aerodynamic and acoustic results are compared to a previous computation involving the Ffowcs Williams and Hawkings approach and show a better agreement with the measurements conducted at the MARTEL facility. A more careful analysis of the pressure field suggests that the noise is strongly influenced by the flame trench geometry. Nonlinear propagation effects, natively taken into account by the full Euler solver, are finally highlighted and discussed. Based on appropriate metrics, a good agreement with the experiment is obtained.

During the lift-off phase of a space launcher, rocket motors generate harsh acoustic environment that is a concern for the payload and surrounding structures. Hot supersonic jets contribute to the emitted noise from both their own noise production mechanisms and their interactions with launch pad components, such as the launch table and flame trenches. The present work describes the results of computations performed by ONERA to predict the lift-off noise from reduced scale models of a flame trench. The results include both unsteady flow solution inside the flame trench and the computed noise on near and far field microphone arrays. Numerical computations involve two in-house codes: the flow solver CEDRE, used in LES mode to accurately predict the noise sources, and the acoustic code KIM to reconstruct the far field noise, thanks to an integral Ffowcs Williams and Hawkings porous surface approach. The computational model exactly reproduces the flame trench configurations used in a test campaign carried out by CNES at the MARTEL facility. Results are discussed and compared with experimental acoustic measurements on 48 microphones. Overall, the numerical results reproduce the acoustic measurements within 3 dB. To further improve these results, work is ongoing on acoustic nonlinear effects.