Downstream fluidic injection based directionally targeted jet noise reduction system

The main aim of this study is to analyze targeted jet noise reduction in a particular direction using controlled asymmetric downstream fluidic injection for a Mach 0.9 nozzle. Targeted reduction in the downward-emitted turbulent mixing noise can be achieved by strategically injecting high momentum fluid downstream of the jet exhaust. The effect of this localized asymmetric mixing enhancement on the far field noise is analyzed and it is observed that significant noise reduction can be obtained in a particular direction of interest. Two types of asymmetric injections-design based and operation asymmetries are outlined and investigated in this study. Detailed Large Eddy Simulations are performed on a hybrid block structured-unstructured mesh to generate the flow field which is then used for far-field noise computation. Aeroacoustic analogy-based formulation is used for computing the far-field noise. Mean flow measurements suggest that jet core lengths are shorter due to the enhanced mixing resulting from fluidic injection. The induced asymmetry due to the fluidic injection gives rise to an asymmetric acoustic field leading to targeted directional noise reduction (≈ 3.5S) in the far field. The advantage of this type of injection scheme is that it allows a certain degree of operational flexibility by allowing the user to choose a preferred direction of noise reduction and injecting fluid accordingly. This can help cut down the injection requirements and the associated thrust penalty with downstream injection, making the setup economically viable for practical implementation.