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RISS 인기검색어
- 검색키워드
- 주제어 : Stability of laminar flows (검색결과 3 건)
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On the Reverse of Streamwise Velocity Deficit in Formation of Boundary-layer Streaks
Suh, Sung-Bu,Boiko, Andrey V.,Chun, H. H. The Korean Association of Ocean Science and Techno 2005 Journal of Ocean Science and Technology Vol.2 No.1
The phenomenon of transformation of streamwise velocity deficit to excess in a near-wall wake behind a flat-plate roughness observed previously in numerous experiments is analyzed qualitatively by means of theories of optimal disturbances based on linearized Navier-Stokes and linearized boundary layer equations. It is shown that the reverse of the velocity deficit can accompany the excitation of a streak and that the formation of two maxima in the disturbance stream wise velocity profiles also observed in the experiments can be a side effect of the streak nonoptimality. An experimental approach aimed to provide quantitative data for comparison with a numerical solution of corresponding initial value problem is suggested.
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The Response of Three-dimensional Boundary Layer over a Swept-wing to a Free Stream Axial Vortex
Suh, Sung-Bu,Boiko, Andrey V.,Lee, Inwon,Chun, H. H. The Korean Association of Ocean Science and Techno 2005 Journal of Ocean Science and Technology Vol.2 No.1
A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is investigated. The response is dominated by streamwise velocity perturbations that grew quasi-exponentially downstream. It is shown that the formation of the boundary layer disturbance occurs for the most part close to the leading edge. The disturbance represents itself a wave packet consisted of the waves with characteristics specific for cross-flow instability. However, an admixture of growing disturbances which origin can be attributed to transient effects and distributed receptivity mechanism is also identified.
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Characteristics of vertically injected buoyant jets of highly diluted propane
K. W. Chun,S. H. Won,J. Kim,정석호 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.4
In coflow jets with the nozzle diameter of O (1 cm) and the fuel jet velocity of O (10 cm/s), the buoyancy induced by the density difference between the fuel and air influences the jet structure appreciably. The present study investigated the behavior of such a buoyant jet numerically and experimentally, especially when the fuel stream had higher density than air. When the fuel jet was composed of propane highly diluted with nitrogen, the fuel jet was decelerated and formed a stagnation region. Consequently, the fuel was carried downstream by the coflow having a circular cone shape. When the fuel was moderately diluted or as the jet velocity increased, numerical results showed the Kelvin-Helmholtz type instability along the mixing layer of the jet. When the fuel jet velocity was relatively high, the stagnation height increased nonlinearly with fuel jet velocity having the power of approximately 1.62. In the relatively high Reynolds number regime of Re > 80, the stagnation height can be correlated to Re0.62 Ri−0.5 , indicating the combined effects of buoyancy and jet momentum. As the Reynolds number becomes small, the stagnation height was affected by the streamwise diffusion due to fuel concentration gradient and by the wake behavior near the nozzle tip. Accordingly, the stagnation heights approach to none-zero values, which were found to be relatively insensitive to fuel dilution.
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