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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.
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.
Time-dependent Evolution of Accretion Disk Mass in a Black Hole Microquasar Candidate A0620-00
김순욱 한국지구과학회 2008 韓國地球科學會誌 Vol.29 No.7
The time-dependent evolution of disk mass for outburst limit cycle in a black hole microquasar is calculated based on the non-linear hydrodynamic model of thermally unstable accretion disk. The physical parameters such as black hole mass, disk size and mass transfer rate are adopted to reproduce the historical 1975 outburst observed in a prototype black hole X-ray nova A0620-00. The time-dependent effect of irradiation from the central hot region to the disk is considered in two ways: direct irradiation and indirect irradiation reflected from hot accretion flow above the disk. The accretion disk thermal instability model can account for the bolometric luminosity appropriate to typical characteristics of system luminosity observed in X-ray transients during the whole cycle of the outburst evolution. The maximum mass of the accretion disk, ~4.03×1024 g, is achieved at the ignition of an outburst, and the minimum value, ~8.54×1023 g, is reached during the cooling decay to quiescence. The disk mass varies ~5 times during outburst limit cycle.