• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.621-627
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• 2008

Aerodynamic data measured in a wind tunnel has inevitable errors due to the presence of the wind tunnel walls. These unwanted interference effects must be corrected for the wall interference free aerodynamic data. Streamline curvature effects are caused by straightening of streamlines due to wind tunnel walls. Classical Glauert's correction method that is a standard method for fixed wing aircraft is not suitable for rotary wing aircraft. In this paper, Heyson's correction method of which wake model is compatible with rotors is used to correct the rotor shaft angle as well as the dynamic pressure. The results of Heyson's method are compared with Glauert's correction method.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.540-546
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• 1992

Turbulent Couette flow between coaxial cylinders with inner one rotating has been investigated experimentally and numerically. The radius ratio of the coaxial cylinders is 0.43. Mean velocity and turbulent stresses have been measured by hot-wire anemometer in the range of Reynolds number based on the velocity at rotating wall and the radial distance between walls, 60,900-187,000. For the numerical computation, the Reynolds stress model has been used as a turbulence closure model. Measurements of mean velocity show that the velocity profile of wall layer largely deviates from universal logarithmic law due to the effect of streamline curvature, especially in the region near the stationary outer cylinder. The results computed with the Reynolds stress model agree well with the experimental data in the prediction of circumferential intensity of turbulent fluctuations. However, the computed level of radial intensity is much higher than the measurement. Curvature-corrected versions of the Reynolds stress model improves the prediction of turbulent intensities, but the results are not fully satisfactory.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.139-146
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• 1996

An extended $k-\varepsilon$ tuebulence model modified by considering the streamline curvature effect and standard $k-\varepsilon$ turbulence model have been applied for three dimensional analysis of turbulece flow in a $90^{\circ}$ curved duct. By comparision of the results with the experimental data, the modified extended $k-\varepsilon$ model gave closer agreement with experimental data than the results from standard $k-\varepsilon$ model owing to an extra time scale of the production rate and parameter describing effects of streamline curvature included in the dissipation rate equation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.440-452
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• 1990

Comprehensive numberical computations have been made for four turbulent swirling jets with and without recirculation to critically evaluate the accuracy and universality of several exising turbulence models as well as of the modified k-.epsilon. model proposed in the present study. A numerical scheme based on the full Navier-Stoke equations ha been developed and used for this purpose. Inlet conditions are given by experiments, whenever possible, to minimize the error due to incorrect initial conditions. The standard k-.epsilon. model performs well for the strongly swirling jets with recirculation while it underpredicts the influence of swirl for weakly swirling jets. Rodi's swirl correction and algebraic stress model do not exhibit universality for the swirling jets. The present modified k-.epsilon. model derived from algebraic stress model accounts for anisotropy and streamline curvature effect on turbulence. This model performs consistently better than others for all cases. It may be because these flows have a strong dependence of stresses on the local strain of the mean flow. The predictions of truculence intensities indicate that this model successfully reflect the curvature effect in swirling jets, i.e. the stabilizing and destabilizing effects of swirl on turbulence transport.

• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.4
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• pp.333-338
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• 2008

The coastal zone is a delicate and dynamic area in which the majority of a water kinetic energy is dissipated. These processes are subsequent to the transport of the beach materials. In comparison to emerged breakwaters, submerged structures permit the passage of some wave energy and in turn allow for circulation along the shoreline zone. This research aims to examine the beach erosion prevention capability of submerged structure by laboratory model. The flow characteristics behind a submerged obstacle with bottom gap were experimentally investigated at Re = $1.2{\times}10^4$ using the two-frame PIV(CACTUS 2000) system. Streamline curvature field behind the obstacle has been obtained by using the data of time-averaged mean velocity information. And the large eddy structure in the separated shear layer seems to have signification influence on the development of the separated shear layer. As bottom gap size increases, the recirculation occurring behind the obstacle moves toward downstream and its strength is weakened.