Secondary growth of three-dimensional mode in the far wake through subharmonic resonance
Thesis/Dissertation
·
OSTI ID:7242541
This study was aimed at understanding the structure and growth of secondary three-dimensional modes in the far-wake region of a two-dimensional bluff body. An airfoil at a 0[degrees] angle of attack was used as the wake producing body in order to reach the far-wake characteristics in a shorter streamwise distance. Perturbations of the basic flow were produced by an array of vibrating elements on the surface of the airfoil. The elements were formed by aluminum strips that were activated by an electro-magnetic system. It was possible to set the amplitudes and initial phase of all the individual elements. These were controlled with software in order to generate time-periodic three dimensional (oblique) wave pairs of equal but opposite wave angle, along with a two-dimensional wave. The frequency of the three-dimensional wave was the subharmonic of the two-dimensional wave. This experiment was performed at a relatively high wake Reynolds number, based on the wake deficit velocity and half-width, of 560. The results include documenting the resonant growth of the three-dimensional subharmonic mode. In addition, comparisons to theory of the eigenfunction modulus and phase for different modes were done. Analysis of the results showed that nonlinear, sum and difference, interactions of the subharmonic mode can account for characteristic changes in the secondary basic flow. The three dimensional structure of the predominant modes is also presented through features in the velocity-tracer particle visualization constructed for the phase averaged velocity field.
- Research Organization:
- Illinois Inst. of Tech., Chicago, IL (United States)
- OSTI ID:
- 7242541
- Country of Publication:
- United States
- Language:
- English
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