Modelling under-expanded jet screech by ILES

Axisymmetric screech from an under-expanded contoured sonic nozzle is modelled by Implicit Large Eddy Simulations (ILES). A self-sustained shear-layer instability develops naturally, without artificial excitation, in the time-marching ILES simulation. This reproduces some of the main flow characteristics of the A2 axisymmetric screech mode documented in experiment. This includes a tonal pressure field, which is resolved by the model. The axisymmetric modelling approach prevents the development of azimuthal structures in the jet shear-layer downstream of the potential core, which are known to be important features for controlling jet mixing and broad-band jet noise.