Spatiotemporally-Resolved Velocimetry for the Study of Large-Scale Turbulence in Supersonic Jets
Saltzman, Ashley Joelle
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The noise emitted from tactical supersonic aircraft presents a dangerous risk of noise-induced hearing loss for personnel who work near these jets. Although jet noise has many interacting features, large-scale turbulent structures are believed to dominate the noise produced by heated supersonic jets. To characterize the unsteady behavior of these large-scale turbulent structures, which can be correlated over several jet diameters, a velocimetry technique resolving a large region of the flow spatially and temporally is desired. This work details the development of time-resolved Doppler global velocimetry (TRDGV) for the study of large-scale turbulence in high-speed flows. The technique has been used to demonstrate three-component velocity measurements acquired at 250 kHz, and an analysis is presented to explore the implications of scaling the technique for studying large-scale turbulent behavior. The work suggests that the observation of low-wavenumber structures will not be affected by the large-scale measurement. Finally, a spatiotemporally-resolved measurement of a heated supersonic jet is achieved using large-scale TRDGV. By measuring a region spanning several jet diameters, the lifetime of turbulent features can be observed. The work presented in this dissertation suggests that TRDGV can be an invaluable tool for the discussion of turbulence with respect to aeroacoustics, providing a path for linking the flow to far-field noise.
General Audience Abstract
During takeoff, the intense noise emitted from tactical supersonic aircraft exposes personnel to dangerous risks of noise-induced hearing loss. In order to develop noise-reduction techniques which can be applied to these aircraft, a better understanding of the links between the jet flow and sound is needed. Laser-based diagnostics present an opportunity for studying the flow-field through time and space; however, achieving both temporal and spatial resolution is a technically challenging task. The research presented herein seeks to develop a diagnostic technique which is optimized for the study of turbulent structures which dominate jet noise production. The technique, Doppler global velocimetry (DGV), uses the Doppler shift principle to measure the velocity of the flow. First, the ability of DGV to measure the three orthogonal components of velocity is demonstrated, acquiring data at 250 kHz. Since turbulent structures in heated jets can be correlated over long distances, the effects on measurement error due to a large field-of-view measurement are investigated. The work suggests that DGV can be an invaluable tool for the discussion of turbulence and aeroacoustics, particularly for the consideration of full-scale measurements. Finally, a large-scale velocity measurement resolved in time and space is demonstrated on a heated supersonic jet and used to make observations about the turbulence structure of the flow field.
- Doctoral Dissertations