Axis-switching in square coaxial jets

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Piffaut, Victor
square coaxial jets; axis-switching
thesis / dissertation description
Airflow from single and coaxial contoured nozzles with a square cross section is studied using constant temperature anemometry. The inner to outer jet velocity ratio is 1.5. The Reynolds number of the outer jet based on the hydraulic diameter of the outer nozzle exit is 15,300. Results are compared to previous data obtained with circular nozzles under the same conditions. Properties of the jets and their shear layers such as turbulence shear layer thicknesses and growth rates were derived from the velocity record. The mixing between the jets and with the external flow was found to be enhanced by passive forcing. Axis switching was observed in the near field of the jets. Fourier space analysis was conducted. Energies of the preferred modes and their harmonics were computed in the shear layers. A sub-harmonic cascade was observed, evidence of non-linear interaction between the preferred mode and its sub-harmonics.