The main aim of this investigation is to estimate the noise reduction using a novel downstream microjet injection scheme. Contrary to previous studies which injected fluid either inside the nozzle or just at the nozzle exhaust, this injection scheme injects multiple equally spaced microjets perpendicular to the jet axis at an axial location downstream from the nozzle exhaust using a coaxial injector tube. Microjet injection closer to the jet axis leads to the formation of counter rotating vortex pair (CVP) close to the injection location which further beaks down into stream-wise vortices as the microjet bends and follows core ow direction. Isothermal jet-injector configuration is tested for a Mach 0.9 single stream nozzle with continuous injection. Instantaneous aerodynamic fields are obtained using Large Eddy Simulation (LES) and the results are validated with previous experimental results. Four different injection pressure ratios are tested in this part of the study and the corresponding effect on far field noise is analyzed. Similarly, simulations are performed for analyzing the effect of number of injection ports on far field noise and various symmetric distributions of microjet ports are studied for its effect on jet mixing noise and subsequent far field noise reduction. The results suggests that the presence of coaxial injector tube significantly alters the flow field leading to shorter jet core and a reduction in the far field noise. When the fluid injection is activated there is a decrease in the turbulence in the jet core due to enhanced mixing, leading to a decrease in the far field mixing noise. Higher injection pressure ratios lead to higher jet trajectories leading to better jet penetration and stronger CVPs in the near field of the injection location. Similarly increasing the number of injection ports leads to higher number of CVPs in the near field and enhanced mixing. The effect of these parameters on mixing characteristics and far field noise is analyzed in this study.