Small Scale Mixing in the Initial Region of a Jet
Final rept. 1985-1986
TEL-AVIV UNIV (ISRAEL) DEPT OF MECHANICAL ENGINEERING
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The possibility of achieving substantial mixing enhancement, using noncircular nozzles, was demonstrated. It was shown that nozzle geometries containing sharp corners are beneficial for mixing purposes. By breaking the initial symmetry of the flow, one may also reduce the coherence of the large structures, thus eliminating the main causes for the onset of combustion instabilities. The excitation of azimuthal instabilities increases the mixing at the higher frequency range. The considerable variation of the mean velocity distribution around the jet, especially near the corners, results in a rapid decrease of the azimuthal cross-correlation near these sections. When such cross-correlation is decomposed into aximuthal modes, higher modes are shown to be present. The higher modes are responsible for the increase in the three- dimensionality of the flow, the turbulence level, and the small scale activity.
- Fluid Mechanics