Control of Jet Flowfield Dynamics.
Annual technical rept. 1 Jan 83-1 Jan 84,
MCDONNELL DOUGLAS RESEARCH LABS ST LOUIS MO
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Passive control of shear layer turbulence was investigated experimentally for low subsonic velocity jets from circular nozzles by studying effects of modifying nozzle exit geometry. Indeterminate origin I.O. nozzles used, including slanted, stepped and crenelated exit geometries, were so designated because streamwise location of the nozzle lip varies with azimuthal position, unlike standard nozzles for which the entire termination is at the same streamwise location. Flow visualization and detailed hot-wire measurements were used to observe development and interaction of large-scale turbulent structures in shear layers originating from various sectors of the I.O. nozzles, to determine the influence of instability wave patterns on ensuing flowfield characteristics and to relate observed evolution of three-dimensional large-scale turbulent structures to global properties of the jet flowfield such as velocity profiles and shear layer spreading rates as a function of streamwise distance and azimuthal angle. Results showed pronounced asymmetries in shear layer growth rates, which could be controlled by varying nozzle parameters. The assymetries were also confirmed by measurements of azimuthal variation of shear layer turbulent energy as well as mean-velocity profiles. Detailed features of energy transfer from the mean flow into successively larger flow structures were traced by spectral mapping techniques and by mapping energy levels contained in subharmonics of the shear-layer instability frequency at various azimuthal flow sectors.
- Fluid Mechanics
- Jet and Gas Turbine Engines