On the generation of turbulent inflow for hybrid RANS/LES jet flow simulations

Abstract The present work is devoted to the assessment of a low-noise turbulence generation methodology used to produce boundary layer with three-dimensional resolved turbulence at the exit of a jet nozzle to reproduce experimental conditions. The method relies on the use of roughness elements introduced in the computational domain with Immersed Boundary Conditions and ZDES mode 3 (Wall Modelled LES branch of ZDES). The simulation of a round jet at M = 0.9 and Reynold number 106 with turbulence generation is compared to a simulation with no resolved turbulence in the nozzle boundary layer using ZDES mode 2. The behaviour of the boundary layer downstream of the roughness elements inside the nozzle is scrutinized using two grids. The turbulence generation method combined with ZDES mode 3 produces satisfying levels of resolved turbulence at the nozzle exit. The early stages of the shear layer development are modified by the ZDES mode 3 simulations providing an initially turbulent shear layer. On the other hand, the ZDES mode 2 simulations, with a turbulent mean exit velocity profile but no resolved turbulence, display a short area of strong shear layer instabilities leading to the quick development of three-dimensional turbulence in the mixing layer. The present results give insights on the level of turbulent modelling of the nozzle boundary layer needed depending on the purposes of the jet flow simulations considered.