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Boiko, Andrey V.,Kulik, Victor M.,Chun, Ho-Hwan,Lee, In-Won The Society of Naval Architects of Korea 2011 International Journal of Naval Architecture and Oc Vol.3 No.4
Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.
Andrey V. Boiko,Victor M. Kulik,Ho-Hwan Chun,이인원 대한조선학회 2011 International Journal of Naval Architecture and Oc Vol.3 No.4
Skin frictional drag reduction efficiency of “stiff” compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.
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.