Numerical study of fluidic injection for noise reduction

We investigate the ability of fluidic injection to control the noise of a model gas-turbine nozzle exhaust. The work is conducted using a hybrid method of LES for the flow field and Lighthill's acoustic analogy for the acoustic field. The impact of injection on the flow development in terms of coherent structures and characteristic frequencies is evaluated. The main results show that a low momentum ratio fluidic injection can trigger a vortex pairing mechanism, resulting in energy transfer to a sub-harmonic of the jet preferred shedding frequency. This changes the development and structure of the flow. The corresponding acoustic sources are shown to be significantly damped. For large directivity angles, the spectral distribution and reduction of Sound Pressure Level is in good agreement with experiments.