The noise from large-scale coherent turbulent structures within jets remains the dominant source. For the purpose of developing future control systems for the large-scale noise source, we investigate the statistics between upstream and downstream radiating waves. We investigate two off-design supersonic jet flows with instability theory and associated noise radiation, large-eddy simulation (LES), and experiments. We compare the auto-correlation, cross-correlation, coherence, and other statistics predicted by aeroacoustic instability theory. As instability waves are closely connected with the formation of large-scale turbulent structures, they yield insight into large-scale noise statistics. We investigate two nozzles at two supersonic off-design conditions. The first is a biconic nozzle operating at an unheated condition, and the second is a NASA nozzle operating at a heated condition. We find that for these jets, the noise from instability waves is coherent between 0.40 to 0.70 at large-scale radiation frequencies between the downstream and upstream radiation directions.
The impact of large-scale turbulent structures on the aerodynamic flow-field and far-field radiated noise is investigated through analysis of an over-expanded supersonic jet. The jet operating conditions are Mj = 1.3 and Reynolds number 1.6 × 106. The Kirchhoff surface (KS) method is used to predict radiated noise based on large-eddy simulation (LES) and applied to calibrate amplitudes of an instability wave model. The acoustic pressure time history in the near- and far-field are constructed with the instability wave model. Predictions are validated with experiment and compare favorably. Cross-correlation and cross-spectral analysis shows that the noise from instability waves is highly correlated the upstream near-field and downstream far-field radiation directions. However, the radiated instability noise in the upstream direction is dominated by fine-scale noise. Results show that it is possible to design a control system for large-scale structure noise based on upstream control if the instability noise can be extracted.
Numerical simulations of non-isothermal multi-interface flow of polymer fluids in circular and annular dies have been carried out. The present finite difference scheme was formulated based on control volume approach to solve the transformed governing equations. The stream function was used as the cross-stream coordinate in these equations. The fluid viscosity is described by a truncated power law with Arrhenius type temperature dependency. Comparisons were made among single phase, two-layer, and three-layer flow in a circular die to demonstrate that the center layer structure difference among them does not make a significant difference in viscous dissipation and nominal shear rate. Also included is the analysis of non-isothermal four-layer concentric coextrusion flow in an annular die.
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