• Journal of Ship and Ocean Technology
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• v.8 no.4
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• pp.10-16
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• 2004

A response of a swept wing boundary layer to a single free-stream stationary axial vortex of a limited spanwise extent is considered as an example of typical problems that one can find in laminar-turbulent transition research and control. The response is dominated by streamwise velocity perturbations that grow 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 whose origin can be attributed to transient effects and to a distributed receptivity mechanism is also identified.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.64-72
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• 1989

Laminar natural convection heat transfer from a horizontal heat exchanger tube with one infinitely long vertical plate fin has been studied by a finite-difference numerical procedure. In predicting convective heat transfer from a circular tube, the thermal boundary condition at solid fluid interface is usually assumed to be isothermal. However, in reality, the thermal boundary condition is not isothermal, and the tube has the thickness and the conductivity. So the temperature at the interface is not known a priori to the calculation. This problem has the conjugate phenomena which occur between the tube conduction and external natural convection, and between the fin conduction and external natural convection. Numerical results are obtained to determine the effects of the conductivity of solid wall and the thickness of tube wall on heat transfer. It is found that the conduction causes significant influence on the natural convection heat transfer at low K and high ${\delta}$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.739-752
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• 1989

The temperature distribution and heat flux of the inner wall of the cylinder of turbocharged gasoline engine were calculated by the 3-dimensional heat conduction analysis employing boundary element method. Overall mean effective heat transfer coefficient and thermal resistance ratio and equivalent thickness of the cylinder wall were calculated. the numerical results were discussed with respect to the engine speed, equivalence ratio, spark and boost pressure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.302-312
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• 1992

Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices

• Resources Recycling
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• v.11 no.3
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• pp.25-30
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• 2002

Heat transfer occurring in the rotary cooler was analyzed by applying a one-dimensional steady state. The temperature of inlet gas and the measured temperature of outlet gas were used as boundary conditions. Axial temperature distribution of solid, gas and wall were calculated by solving two differential equations and two algebraic equations under the constraint of two point boundary conditions and operating conditions. The temperatures of outer wall calculated in this study were in good agreement with those measured from running rotary cooler.

• Journal of Hydrospace Technology
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• v.1 no.1
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• pp.41-56
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• 1995

Flew control devices, such as flow liners, are frequently introduced in a cavitation tunnel in order to reduce the tunnel blockage effect, when a three-dimensional wake distribution is simulated using a complete ship model or a dummy model. In order to estimate the tunnel wall effect and to evaluate the effect of flow liners on the simulated wake distribution, a surface panel method is adopted for the calculation of the flow around a ship model and flow liners installed in a rectangular test section off cavitation tunnel. Calculation results on the Sydney Express ship model show that the tunnel wall effect on the hull surface pressure distribution is negligible for less than 5% blockage and can be appreciable for more than 20% blockage. The flow liners accelerate the flow near the afterbody of the ship model, so that the pressure gradient there becomes more favorable and accordingly the boundary layer thickness would be reduced. Since the resulting wake distribution is assumed to resemble the full scale wake, flow liners can also be used to simulate an estimated full scale wake without modifying the ship model. Boundary taper calculation should be incorporated in order to correlate the calculated wake distribution with the measured one.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2660-2665
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• 2007

Turbulent boundary-layer over a micro-riblet film(MRF) was investigated experimentally. The MRF has sharp V-shaped micro scale grooves of $300{\mu}m$ in width and $176.8{\mu}m$ in height. Particle image velocimetry(PIV) system was employed to measure velocity fields of flow over the MRF coated plate. Flow over a smooth plate was also measured for comparison. The PIV measurements were taken in the streamwise wall-normal planes at Re$\theta$= 985 and 2342. Vortex structures of the flow were analyzed by extracting the swirling strength as an unambiguous vortex-identification criterion. As a result the number of spanwise vortices with clockwise(negative) rotation decreases rapidly in the near-wall region(y<0.2h), but decreases slowly in the outer region(0.2h

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.931-939
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• 2001

The slot coupling characteristics was analysed in a radial-line slot antenna for its design. The previously proposed waveguide model with a periodic boundary condition on its narrow walls and periodically arranged slots on its wide wall was used. The magnetic field integral equation and two dyadic Green\`s functions for respective regions was derived and the method of moments was used. To maximize the efficiency of numerical analysis and to extract singularities, two different kinds of basis functions, the entire domain basis function and the sub-domain one, are used. In addition, the Ewald sum technique for the rectangular waveguide and the Shanks transform for the half space were used to accelerate the computation of the slowly convergent potential Green\`s functions. Simulation results expressed the effects of the various design parameters on the slot coupling.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.2
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• pp.127-153
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• 2012

This paper presents an advanced computational method for the prediction of the responses in the frequency domain of general linear dissipative structural-acoustic and fluid-structure systems, in the low-and medium-frequency domains and this includes uncertainty quantification. The system under consideration is constituted of a deformable dissipative structure that is coupled with an internal dissipative acoustic fluid. This includes wall acoustic impedances and it is surrounded by an infinite acoustic fluid. The system is submitted to given internal and external acoustic sources and to the prescribed mechanical forces. An efficient reduced-order computational model is constructed by using a finite element discretization for the structure and an internal acoustic fluid. The external acoustic fluid is treated by using an appropriate boundary element method in the frequency domain. All the required modeling aspects for the analysis of the medium-frequency domain have been introduced namely, a viscoelastic behavior for the structure, an appropriate dissipative model for the internal acoustic fluid that includes wall acoustic impedance and a model of uncertainty in particular for the modeling errors. This advanced computational formulation, corresponding to new extensions and complements with respect to the state-of-the-art are well adapted for the development of a new generation of software, in particular for parallel computers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1639-1644
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• 1990

Effects of radiation on the wall-friction and heat transfer in the convergent and divergent nozzle of a rocket motor are investigated in the present paper. Radiative heat transfer cools down the core gas, and the decrease in the gas temperature reduces the convective heat transfer on the wall. Radiation heat transfer is estimated by using mean-beam-length approach and core flow is assumed to be one-dimensional isentropic. The compressible thermal boundary layer is solved by a finite difference method. The Cebeci-Smith eddy viscosity model is adopted for the present study. Convective heat transfer is reduced at the throat of the nozzle and is almost compensated with an increase in radiative transfer. In the sequel total heat transfer rate is slightly reduced. However, radiation heat transfer is dominant in the converging part of the nozzle.