“Acoustic Characteristics of a Supersonic Twinjet Configuration”
Publication Type:
Conference
Authors:
Co-Authors:
K. Goparaju and D. Gaitonde
Year Published:
2018
Abstract:
A twin-jet configuration consists of two jets placed in closed proximity to each other. In our previous effort,we employed Large Eddy Simulations (LES) to study the turbulent features of a perfectly expanded M= 1.23circular twin-jet configuration with an inter-nozzle spacing of two jet diameters. In the current work, we examine theacoustic characteristics of this configuration, using a general decomposition technique. In agreement with previousexperimental efforts, the near-field pressure fluctuations along the plane containing the jet axes indicate jet noiseshielding, where the noise levels due to the twin-jet is less than the sum of two incoherent single-jets. This shieldingeffect is observed to diminish with increasing polar angles. On the other hand, no such shielding is observed alongthe plane perpendicular (φ= 90o) to that containing the jet axes and instead noise level amplification, relative tothe sum of two incoherent single-jets, is observed. This is attributed to the unabated sound radiation of the twin-jet plume in this direction. To aid in the identification and understanding of the noise generation mechanisms, inaddition to predicting the radiated noise levels and directivity, a decomposition of the flow-field into constituent fluid-thermodynamic (FT) modes i.e., acoustic, hydrodynamic and thermal components, using Momentum Potential Theory(MPT). The decomposed hydrodynamic mode is observed to represent the vortical features in unsteady turbulence,and displays a dominant m= 1 helical mode. The noise signature associated with these turbulent features is containedin the decomposed acoustic mode, which exhibits a pronounced wavepacket structure in the jet core, with an apparentm= 0 axisymmetric toroidal mode dominance. Consistent with recent works on perfectly expanded supersonic jets,the acoustic wavepacket exhibits significant temporal and axial modulation, which play a major role in determiningacoustic radiation characteristics such as directivity and intermittency. The decomposed results provide insights intothe manner in which the two wavepackets interact with each other, both immediately downstream of the jet exit,where each wavepacket has a distinct identity, as well as further downstream where they merge to form a single entity.Qualitative and quantitative agreement is observed between the near-field noise levels predicted by the acoustic modeand the overall pressure fluctuations. The decomposed acoustic mode correctly predicts shielding and magnificationphenomena, which demonstrates its ability to predict acoustic behavior, even in very complex configurations
Conference Name:
2018 AIAA/CEAS Aeroacoustics Conference, AIAA Aviation Forum
Conference Location:
Atlanta, Georgia
Other Numbers:
Refereed Designation:
Date Published:
6/24/2018