• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.235-240
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• 1995

The paper describes hypersonic rarefied flow of helium and nitrogen over a flat plate by the direct simulation Monte Carlo (DSMC) method. The effect of incomplete accommodation and plate thickness are analyzed and the computational results are compared with wind tunnel test data. Also computational aspects of the method are outlined.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1625-1630
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• 2004

An experimental study was carried out to investigate influence of flow conditions on a boundary layer to the near-wake of a flat plate. The flow condition in the vicinity of trailing edge that is influenced by upstream condition history is an essential factor that determines the physical characteristics of a near-wake. Various tripping wires were used to change boundary layer flow condition of upstream at the freestream velocity of 6.0 m/sec. Measurements of the boundary layer and near-wake according to the change of upstream conditions were conducted by using both I-probe(55P14 for boundary layer) and X-probe(55P61 for wake). Normalized velocity profiles of the boundary layer were shown the flow types such as laminar boundary layer, transition, and turbulent boundary layer at 0.95C from the leading edge. The velocity and turbulence intensity profiles of the near-wake for the case of laminar boundary layer at the flat plate surface exhibited a defect and a double peak showing perfect symmetry, respectively.

• Journal of the Korean Solar Energy Society
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• v.27 no.3
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• pp.149-154
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• 2007

It is essential to know the heat transfer characteristics at the absorber plate of Flat-plate solar collector for optimum design. For flat-plate solar collector, it is difficult to experimentally study the effect for the Reynolds number of riser considering low mass flow rate being applied into the collector with one riser tube. So, this study were performed to show the heat transfer characteristics of flat-plate solar collector with single absorber plate and riser for various Reynolds number at riser using commercial code FLUENT 6.0. The base collector size is chosen with $0.4m^2$ as 0.2m by 2m with single riser in this study, Reynolds number at riser is from 200 to 1200 including about 530 at typical flat-plate collector with 10 risers considering the mass flow rate of 0.02kg/s per collector area for the certificate test Through the simulation, the results were presented as the temperature distribution at the absorber plate for various flow rate and solar irradiance conditions, then showed the effective length scale of the absorber plate The real solar irradiation condition is assumed as the constant heat flux condition of $500w/m^2$ considering the annual average solar irradiance in Korea.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.739-742
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• 2002

The supersonic, dual, coaxial jet impinging upon a vertical flat plate has recently been applied to a variety of industrial manufacturing processes, since it has several advantages over a conventional supersonic impinging jet. In the present study, experimentation is carried out to investigate the effects of the impinging angle of the annular flow and the design Mach number on the flow field formed over the vertical flat plate. A convergent-divergent nozzle is used to obtain the inner jet flow, its design Mach number being changed between $1.0\;and\;2.0$. The outer annular nozzle has a constant area of the Mach number of 1.0, and its impinging angle of $0^{\circ}\;and\;20^{\circ}$. The primary jet pressure ratio is changed in the range from 6.0 to 10.0 and for the annular flow, the assistant jet pressure ratio is changed from 1.0 to 4.0. The distance between the dual, coaxial nozzle and flat plate is also changed. Detailed pressure measurements are conducted along the axis of the jet and on the flat plate as well. The impinging coaxial Jet flows are visualized using the Schlieren and Shadow optical methods. The results show that the flow field on the plate is not strongly dependent only on the primary and assistant pressure ratios but also the impinging angle of the annular nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1073-1084
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• 1999

The effects of secondary flow on the structure of a turbulent wake generated by a flat plate was investigated experimentally. The secondary flow was induced In a $90^{\circ}$ curved duct in which the flat plate wake generator was installed. The wake generator was installed in such a way that the wake velocity gradient exists in the span wise direction of the curved duct. Measurements were made in the plane containing the mean radius of curvature where pressure gradient and curvature effects were small compared with the secondary flow effect. All six components of the Reynolds stresses were measured in the curved duct. Turbulence intensities in the curved wake are higher than those in the straight wake due to an increase of the turbulent kinetic energy production by the secondary flow. In the inner wake region, shear stress and strain in the plane containing the velocity gradient of the wake show opposite signs with respect to each other, so that eddy viscosity Is negative in this region. This indicates that gradient-diffusion type turbulence models are not appropriate to simulate this type of flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.4
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• pp.417-427
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• 1998

The effect of secondary flow on the heat transfer of a turbulent wake generated by a flat plate was experimentally investigated. The secondary flow was induced in a curved duct in which the flat plate wake generator was installed. All three components of turbulent heat flux were measured in the plane containing the mean radius of curvature of the curved duct. The results showed that mean temperature profiles deviate from the similarity of the straight wake because of the cold fluid transported from the free-stream. The half-width of the mean temperature profile increased rapidly by upwash motion of the secondary flow. The changes to turbulence structure caused by the secondary flow show more pronounced effect on heat transport than on momentum transport. This is because the response to the variation of flow conditions is delayed in temperature field. Negative production of the turbulent heat flux is observed in the inner wake region. From the conditional averaging, it has been found that the negative production of the turbulent heat flux is generated due to a mixing process between the hot and low momentum eddies occupied in the inner wake region and the cold and high momentum eddies in the potential region.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.319-322
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• 2006

Rapid mixing of air-fuel (<1 ms) is needed to accomplish supersonic combustion. In this experiment, helium was injected laterally in to the Mach 1.92 air flow. 2 kinds of model, flat plate/cavity, were used in this experiment and images were taken by schlieren visualization. Pressure was affected by shock structure in the supersonic duct, and penetration height was increased by increasing J. Penetration height was higher in the cavity model than flat plate model.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.193-201
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• 1998

A heat exchanging system employing the impinging air jet is still widely used In the various fields due to its inherent merits that include the easiness in engineering applications and the high heat and/or mass transfer characteristics. The purpose of this study is to investigate the enhancement of heat transfer and flow characteristics by placing a turbulence promoters in front of heat exchanging surface. In this study, a series of circular rods are placed at the upstream of a flat plate heat exchanger that is located at potential core region(H/W=2) of a two-dimensional impinging air jet. Heat transfer enhancement is achieved by inserting turbulence promoter that results in the flow acceleration and disturbance of boundary layer. The average Nusselt number of the flat plate with the turbulence promoters is found to be around 1.42 times higher than that of the flat plate without the turbulence promoters. Based on the results of flow visualization with a smoke wire, it is confirmed that the heat transfer enhancement is caused by the flow separation and disturbance of boundary layer by inserting the turbulence promoter.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2329-2338
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• 1993

An accurate analysis procedure to solve the flow about a flat plate at various incidences has been developed. The Navier-Stokes equations of stream function and vorticity form are solved in a sufficiently large computational domain, in which the grid lines are mutually orthogonal. The details of the flow near the singularity at the tip of the plate is well captured by the analytic solution which is asymptotically matched to the numerically generated outer solution. The solution for each region is obtained iteratively : the solution of one (inner or outer) region uses that of the other as the boundary condition after each cycle. The resulting procedure is accurate everywhere and also computationally efficient as the singularity has been removed. It is applied to the flat plate for a wide range of Re : the results agree very well with the existing computation and experiment.

• Journal of KSNVE
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• v.10 no.6
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• pp.1035-1040
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• 2000

The Impingement of a weak shock wave discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Computations predicted the experimented results with a good accuracy. The peak pressure on the flat plate was not strongly dependent of the shock wave Mach number in the present range of Mach Number from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.