| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1995: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1994: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
In the Present study, boundary-layr transition trggered by high-intensity hairpin eddies is examined experimentally. Our knowledge of the boundary-layr response to such high-intensity disturbances is crucial for understanding the attachment-line contamination on a swept wing. In addition, the results give much information on the mechanism of wall turbulence generation and the related critical flow condition.
First examined is the subcritical boundary-layr transition triggered by the hairpin eddies generated at the leading-edge of a boundary-layr plate acoustically. The results clearly showed that when the near-wall flow is disturbed by energetic hairpin eddies, successive growth of hairpin eddies from the lifted-up near-wall shear-layr can occur only beyond the Reynolds number (based on the momentum thickness) R_<rheta>=130-150.
Next examined is the disturbance growth through introducing well-controlled hairpin eddies by using a wall orifice at the station below and around the critical station cited above. In this (subcritical) transition, wall turbulence develops only along a narrow strip extending downstream from the wall orifice, that is, the lateral turbulent contamination is very weak at such low Reynolds numbers. Indeed, the lateral spreading angle (half angle) of turbulent patch is only about 2 deg in the transition region below the x-Reynolds number R_x=1*10^5 ; which is much smaller than the typical value (about 10 deg) for the lateral growth of turbulent spot or wedge. With slightly increasing the Reynolds number, the lateral spreading angle is much increased, about 4 deg for R_x=1.1-1.7*10^5 and about 6.5 deg for 2.0-2.8*10^5. It is also found that in the process of the lateral growth (contamination), the spanwise spacing of hairpin eddies is about 100 in terms of the local wall unit.
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