The noise generated by a hot single stream jet at Mach number M_j=0.7 and diameter-based Reynolds number Re_D= 400, 000 is investigated numerically. No artificial triggering of the flow is present and focus is given on the influence of internal and external boundary layers resolution on noise radiation for both static and take-off configurations. Simulations include the nozzle geometry and are performed for two distinct grids, the first one supporting the flow resolution near the wall whereas no boundary layers resolution is present for the second one. Uniform flow profiles are imposed at the inlet and the flow develops freely. All simulations exhibit low turbulence levels inside the nozzle at the throat, despite the transitional boundary layer observed with the resolution of the near-wall flow. Flow investigations downstream of the nozzle exit highlight the initially laminar development of the flow, especially without boundary layers resolution. The turbulent transition is fastened with boundary layers resolution in the presence of the external flow thanks to the turbulence developed on the external wall that triggers the flow. In the far field, both static simulations overestimate the radiated noise in the medium-frequency range especially because of the additional noise source coming from the initially laminar shear layer development. A similar overestimation is observed with the external flow when the boundary layers are not resolved. With the boundary layers resolution, this additional noise is suppressed and a good agreement is obtained with the experiments.
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