Experimental Investigation on the Acoustic Field and Convection Velocity of Structures in a Heated Jet With Centered Thermal Non-Uniformity

Effect of fluid injection on turbulence and noise reduction of a supersonic jet

“…This suggests an upstream shift in noise sources using the fluid inserts and is indicative of enhanced mixing due to the application of fluid injection. Moreover, it is also seen that the size of the coherent structures is smaller in the case of the 3FC-2FI jet than the baseline jet, which is in accordance with the observations using the Q-criterion in [16] and the SPOD analysis of pressure presented earlier. Further analyses using the acoustic FT mode are being pursued and may yield additional details about the noise reduction mechanism of fluid inserts.…”

“…This indicates that the use of fluid inserts shifts the energy percentage from the spatially coherent modes to the modes that exhibit more incoherent features. This provides further quantitative evidence to the Q-criterion observations in [16] that fluid inserts break up the large-scale structures that are the chief contributors of noise in the peak noise radiation direction. This argument is however based on higher cross-correlation values of the azimuthally coherent component with the far-field pressure.…”

“…The most successful fluid insert nozzle configuration to date contains three fluid inserts, each containing two injectors distributed uniformly around the nozzle azimuth. Coderoni et al [16] have shown previously, through visualization using the Q-criterion, that this fluid insert nozzle generates streamwise vortices that help reduce the size of the largescale structures. They also showed that this fluid insert nozzle breaks down the shock cells, which helps in reducing BBSAN.…”

“…Active noise reduction technologies, on the other hand, may require some redesign of the original jet engine, but these can be switched off or modified after take-off to minimize any performance penalty on the aircraft during flight. Although recent efforts have been made on the development of active noise reduction techniques that do not require any additional hardware [5], most of the current active noise reduction technologies rely on the use of some kind of fluid injection in and around the nozzle exit [6][7][8][9][10]. One such active, though steady, noise reduction technology is the use of fluid inserts in the divergent section of a CD nozzle.…”

“…Although considerable research has been performed to explore the effects of fluid inserts on the jet exhaust, both in the form of experiments [11][12][13][14] and computations [15][16][17], the available data have been found to be insufficient to correlate the noise benefit with changes in the flow-field due to the noise reduction device. The present study is an extension of previous research on fluid inserts that uses large eddy simulation (LES) with the Ffowcs Williams-Hawkings (FWH) analogy for far-field noise prediction.…”