Measurements of spanwise scale change in a forced mixing layer
| Autor: | Richard L. Leboeuf, Rabindra D. Mehta |
|---|---|
| Rok vydání: | 1995 |
| Předmět: | |
| Zdroj: | Journal of Fluid Mechanics. 293:305-319 |
| ISSN: | 1469-7645 0022-1120 |
| DOI: | 10.1017/s0022112095001728 |
| Popis: | Spanwise scale changes of the streamwise vortical structure in a plane forced mixing layer have been investigated through direct measurements. Detailed three-dimensional phase-averaged measurements were obtained of the spanwise and streamwise vorticity in a forced mixing layer undergoing three spanwise roller pairings. A two-stream mixing layer with a velocity ratio (U2/U1) of 0.6 and laminar initial boundary layers was generated in a mixing-layer wind tunnel. Acoustic forcing, consisting of a fundamental roll-up frequency and its first, second and third subharmonics, was used to phase-lock the initial development and the first three pairings of the spanwise rollers. Although the overall spanwise scale remained unchanged through the first two roller pairings, some (cyclic) ‘readjustment’ of the weaker streamwise structures was observed. The overall spanwise scale doubled during the third roller pairing. For the first time, one of the proposed mechanisms for the scale change has been identified and its details measured directly. The weakest (positive) streamwise vortex is split into two and displaced by stronger neighbouring (negative) vortices. These two vortices (of the same sign) then merge together, thus doubling the spanwise scale and circulation of the resulting streamwise vortical structure. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|