On the characterization of noise sources in supersonic shock containing jets.

摘要

Research on the noise produced by military aircraft has seen a renewed interest due to the increasing concerns of communities around airbases and airports. Radiated noise associated with high-speed military style engines is the main contributor of the overall noise produced by modern aircraft, especially in military applications where the jets typically are at very high velocity and temperature, and have low bypass ratios. The acoustic and aerodynamic properties of high-speed jets are investigated experimentally in this thesis. Measurements are conducted in the Penn State high speed jet noise facility, after the validation of the newly upgraded rig. Axisymmetric Nozzles are investigated as well as nozzles with a military style shape.;The database of flow measurements in supersonic shock containing jets is very scarce. This research focuses on performing flow measurements in shock containing jets in an effort to obtain valuable parameters for the modeling of the noise propagated by such flows. Mean flow measurements of the jets are performed with pitot probes traversing the flow. These measurements are used as a qualification tool for a CFD simulation of the flow field with good overall agreement. Measurements in supersonic rectangular jets also uncover the presence of axes switching in fully, over- and under-expanded cases, with the location of this axes switch being further downstream in the fully expanded case. Acoustic data are gathered in shock containing screeching jets. Different techniques are investigated in order to provide some reduction of the screech tones. Optical Deflectometry measurements are performed in shock containing jets and show that the screech tones have no effect on the properties of the convecting structures. On the other hand, the strength of the shock present in the flow seems to have an effect on the convection velocity. Finally, the simultaneous correlation between the flow field fluctuations and the acoustic far field is measured. This suggests that the OD sensors can be used for localizing the noise generation in the jet. Preliminary results of this kind show that the highest frequencies are generated close to the exit plane of the nozzle.