• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.11
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• pp.747-754
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• 2022

An experimental study was carried out to control a shock-induced boundary layer separation by utilizing the supersonic sweeping jet from the fluidic oscillator. High-speed schlieren, surface flow visualization, wall pressure measurement and precise Pitot tube measurement were applied to observe the influences of the location and the supply pressure of the fluidic oscillator on the characteristics of the oblique-shock-induced boundary layer separation. The characteristics of the separation control by the present supersonic fluidic oscillator was quantitatively analyzed by comparing with a conventional control method utilizing an air-jet vortex generator.

• Journal of Ship and Ocean Technology
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• v.8 no.4
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• pp.1-9
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• 2004

High lifting devices used for control purposes have received much attention in the marine field. Hydrofoils for supporting the hull, roll stabilizer fins for developing the motion damping performance, rudders for maneuverability are the well-known devices. In the present study, the ability of the rudder with flap to produce high lift was analyzed. The boundary layer control, one of the flow control techniques, was adopted. Especially, to build the blown flap, a typical and representative type of a boundary layer control, a flapped rudder was designed and manufactured so that it could eject the water jet from the gap between the main foil and the flap to the flap surface tangentially. And it was tested in the towing tank. Simultaneously, to know the information about the 2-dimensional flow field, a fin model with similar characteristics as the rudder model applicable for the motion control was made and tested in the cavitation tunnel. In addition, local flow measurements were carried out to obtain physical information, for example, a surface pressure measurement and flow visualization around the flap. And CFD simulation was used to obtain information difficult to collect from the experiment about the 2-dimensional flow.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.32-40
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• 2003

An experimental research has been carried out for flow visualizations of the shock wave/turbulent boundary-layer interaction control utilizing the aeroelastic flaps, Spark shadowgraphs, kerosene-lampblack tracings for the surface streakline pattern, and interference fringe patterns over a thin oil-film applied at the downstream of the shock interactions have been obtained , Effects of variation of the shapes and thicknesses of the flaps are tested, and all the results are compared to the solid-wall reference case without flow-control mechanism , From the qualitative observation of the variation of skin friction utilizing the interference fringe patterns over the silicone oil-film, a strong spanwise variation of the skin friction with a narrow and long region of separation has been noticed near the centerline behind the shock structure, which phenomenon demonstrate a strong three-dimensionality of the shock interaction flows, Influence of the shape of the cavity under the flaps to the shock interaction is also tested, and it is observed that the shape of the cavity is not negligible.

• Journal of computational fluids engineering
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• v.6 no.4
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• pp.15-25
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• 2001

Numerical prediction of the diffusion controlled transition in a turbine gas pass is important because it can change the local heat transfer rate over a turbine blade as much as three times. In this study, the gas flow over turbine blade is simplified to the flat plate boundary layer, and an adaptive grid scheme redistributing grid points within the computation domain is proposed with a great emphasis on the construction of the grid control function. The function is sensitized to the second invariant of the mean strain tensor, its spatial gradient, and the interaction of pressure gradient and flow deformation. The transition process is assumed to be described with a κ-ε turbulence model. An elliptic solver is employed to integrate governing equations. Numerical results show that the proposed adaptive grid scheme is very effective in obtaining grid independent numerical solution with a very low grid number. It is expected that present scheme is helpful in predicting actual flow within a turbine to improve computation efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.2
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• pp.18-25
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• 2007

Computational study on the passive control of the oblique shock-wave/turbulent boundary-layer interaction utilizing slotted plates over a cavity has been carried out. The numerical boundary layer profile upstream of the interaction follows the compressible turbulent boundary-layer theory reasonably well, and the other results also show good agreements with the experimental observations, such as the wall surface pressures and Schlieren flow visualizations. Further, the effects of various slot configuration including number, location and angle of the slots on the characteristics of the interactions, such as the variation of the total pressures, the boundary-layer characteristics downstream of the interaction and the recirculating mass flux through the slots, are also tested and compared.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.9
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• pp.843-852
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• 2000

The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta winglet protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from $\pm20\;degree\;to\;\pm45$ degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. By using the method mentioned above, the following conclusions were obtained from the present experiment. The boundary layer was thinned in the regions where the secondary flow was directed toward the wall and thickened where it was directed away from the wall. The peak augmentation of the local heat transfer coefficient occurred in the downwash region near the point of minimum boundary-layer thickness.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1025-1031
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• 2012

The present paper deals with concept design of supersonic inlet based on compressible flow theory and flow control of bleeding in order to guarantee stability of supersonic inlet of ramjet engine in broad range of operating conditions. Shock instability, shock wave-boundary layer interaction and flow separation should be properly controlled to improve performance of the supersonic inlet. Considering shock strength, boundary layer and flow separation, the supersonic inlet is modified from the basic model which is designed under inviscid theory. Consequently, shock is stabilized, and required mass flow rate is obtained. Furthermore, bleeding is applied to the supersonic inlet to maintain performance in off-design conditions. Mass flow condition is adopted for modeling of bleeding effect, and performance of the supersonic inlet is evaluated by changing bleeding locations and numbers.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.328-331
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• 2004

Shock wave boundary layer interactions can make flows around a vehicle be very high pressure and temperature due to pass shock waves in small areas of the hypersonic vehicle. These phenomena can affect a critical problem in the design of hypersonic vehicles. To research the effect of shock wave boundary layer interactions, comer flows were studied in this paper using numerical studies with the NSMB (Navier-Stokes Multi Block) solver and then comparing corresponding numerical results with experimental data of the Huston High Speed Flow Field Workshop II. The mach number of flows is 12.3 in comer flows. The comparison with the computational result is presented based on diverse numerical schemes. Good agreement is obtained.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.288-297
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• 2000

This paper describes the results of an experimental investigation of the flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices. The test facility consists of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta wings(vortex generators) protruding from the surface. In order to control the strength of the two longitudinal vortices, the angles of attack of the vortex generators are varied from 20 degree to 45 degree, but spacings between the vortex generators are fixed to 4 cm. The 3-dimensional mean velocity downstream of the vortex generators is measured by a five-hole pressure probe, and the hue-capturing method using the thermochromatic liquid crystals has been used to provide the local distribution of the heat transfer coefficient. By using the method mentioned above, the following conclusions are obtained from the present experiment. The boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall. The peak augmentation of the local heat transfer coefficient occurs in the downwash region near the point of minimum boundary-layer thickness. Streamwise distributions of averaged Stanton number on the measurement planes show very similar trends for all the cases(${\beta}=20^{circ},\;30^{\circ}\;and\;45^{\circ}$).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.82-93
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• 2002

The effects of the interaction between the flow and temperature field and a boundary layer due to a variety of the height of a vortex generator are experimentally investigated. The test facility consists of a boundary-layer wind tunnel with the vortex generator protruding from the bottom surface. In order to control the strength of the longitudinal vortices, the angle of attack and the spacing distance of the vortex generator are 20 degree and 40 mm, respectively. The height of the vortex generator (H) is 15 mm, 20 mm and 30 mm and the cord length of it is 50 mm. Three-component mean velocity measurements are made using a 5-hole probe system and the surface temperature distribution is measured by the hue capturing method using thermochromatic liquid crystals. By using the method mentioned above, the following conclusions are obtained from the present experiment. The boundary layer is thinned in the downwash region where the strong downflow and the lateral outflow of the boundary layer fluid occur and thickened in the upwash re,3ion where the longitudinal vortex sweeps low momentum fluid away from the bottom surface. In case that the height of the vortex generator increases, the averaged circulation and the maximum vorticity of the vortex pair decrease. The contours of the non-dimensional temperature show the similar trends fur all the cases (H=15 mm, 20 mm and 30 mm). The peak augmentation of the distribution of the local non-dimensional temperature occurs in the downwash region near the point of minimum boundary-layer thickness.