An experimental investigation of unexcited and exicted elliptic jets
Abstract
The turbulence characteristics of moderate aspect-ratio (2:1 and 4:1) ellpitic jets were studied via hot-wire anemometer field measurements and flow-visualization. The investigations were carried out for laminar and turbulent boundary layers at the jet exit. It is found that the locations and number of switchovers of axes of the elliptic jet cross-section are strong functions of the initial condition and the aspect ratio. These two can also be altered via controlled excitation depending on the excitation Strouhal number. It is found that in the presence of large variations in exit momentum thickness along the nozzle perimeter, the momentum thickness in the minor-axis side controls the natural instability of the elliptic shear layer. Coherent structures in elliptic jets are characterized by the preferred-mode and the stable pairing mode. The respective Strouhal numbers associated with these two modes scale with the equivalent diameter of the jet. Based on D(3) the preferred code and stable pairing mode Strouhal numbers are found to be 0.4 and 0.85 respectively--the same values also found previously for circular jets hot-wire measurements, and the structure properties (phase-average velocities, coherent vorticity, incoherent turbulence intensities, coherent and incoherent Reynolds stresses, coherent production, etc.) are studied.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- June 1984
- Bibcode:
- 1984PhDT........40H
- Keywords:
-
- Ellipticity;
- Flow Visualization;
- Hot-Wire Anemometers;
- Jet Flow;
- Turbulent Jets;
- Aspect Ratio;
- Laminar Boundary Layer;
- Reynolds Stress;
- Strouhal Number;
- Thickness;
- Turbulent Boundary Layer;
- Fluid Mechanics and Heat Transfer