LES study of noise and its sources of closely installed jets

When a jet is closely installed under a solid surface, turbulent jet plume is modified. Two levels of jet-plate interactions are present. In addition to linear evanescent instability wave scattered by the plate trailing edge, nonlinear jet turbulence strongly interacts with the plate underneath surface. Both of the interactions could lead to far-field noise change but with different mechanisms. Large-Eddy Simulation (LES) has been performed on two installed jets and one baseline isolated jet to investigate the noise generation mechanisms for this closely installed jet. The distance between jet and plate surface is adjusted for the two installed jets so that strong hydrodynamic interaction is only present in one of the configurations. Far-field noise, computed using Ffowcs Williams-Hawkings (FW-H) equations, is compared for the two installed jets to show the effect of close installation. The near-field sound sources are exmined by analysing quadrupole souces of turbulent mixing and dipole sources of unsteady plate surface loading.