• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.100-107
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• 2010

This paper gives new conceptual descriptions of drag reduction mechanism owing to rotating wheel and moving ground condition when dealing with automotive aerodynamics. Using Computational Fluid Dynamics (CFD), flow simulation of three dimensional automobile configuration made by Vehicle Modeling Function (VMF) is performed and the influence of wheel arch, wheels, rotating wheel & moving ground condition to the automotive aerodynamic performance is analyzed. Finally, it is shown that rotating wheel & moving ground condition decreases automotive aerodynamic drag owing to the reduction of the induced drag led by the decrease of COANDA flow intensity of the rear trunk flow.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.57-65
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• 2009

An efficient and high-fidelity design approach for wing-body shape optimization is presented. Depending on the size of design space and the number of design of variable, aerodynamic shape optimization process is carried out via different optimization strategies at each design stage. In the first stage, global optimization techniques are applied to planform design with a few geometric design variables. In the second stage, local optimization techniques are used for wing surface design with a lot of design variables to maintain a sufficient design space with a high DOF (Degree of Freedom) geometric change. For global optimization, Kriging method in conjunction with Genetic Algorithm (GA) is used. Asearching algorithm of EI (Expected Improvement) points is introduced to enhance the quality of global optimization for the wing-planform design. For local optimization, a discrete adjoint method is adopted. By the successive combination of global and local optimization techniques, drag minimization is performed for a multi-body aircraft configuration while maintaining the baseline lift and the wing weight at the same time. Through the design process, performances of the test models are remarkably improved in comparison with the single stage design approach. The performance of the proposed design framework including wing planform design variables can be efficiently evaluated by the drag decomposition method, which can examine the improvement of various drag components, such as induced drag, wave drag, viscous drag and profile drag.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.4
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• pp.313-321
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• 2005

Drag coefficient is one of the critical design factors to quantify the piston effect in vehicle tunnels. Several problems are raised on the drag coefficient currently applied for the ventilation system design; unverified adoption of the projected frontal area of the vehicle from the foreign study in the past, and lack of consideration for the slip-streaming effect. This study aims at better estimation of the traffic-induced ventilation force in the local tunnels. Values for the projected frontal area of the vehicles running on the local roads at present are proposed and results of an extensive CFD study are studied on the slip-streaming effects in various traffic conditions to quantify $K_{blockage}$ and the drag coefficient in the domestic tunnels.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.101-104
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• 2008

The sailfish is the fastest sea animal, reaching its maximum speed of 110km/h. On its skin, a number of V-shaped protrusions pointing downstream exist. Thus, in the present study, the possibility of reducing the skin friction using its shape is investigated in a turbulent boundary layer. We perform a parametric study by varying the height and width of the protrusion, the spanwise and streamwise spacings between adjacent ones, and their overall distribution pattern, respectively. Each protrusion induces a pair of streamwsie vortices, producing low and high shear stresses at its center and side locations, respectively. These vortices also interact with those induced from adjacent protrusions. As a result, the drag is either increased or unchanged for all the cases considered. In some cases, the skin friction itself is reduced but total drag including the form drag on the protrusions is larger than that of a smooth surface. Since the shape of present protrusions is similar to that used by Sirovich and Karlsson [Nature 388, 753 (1997)] where V-shaped protrusions pointing upstream were considered, we perform another set of experiments following their study. However, we do not obtain any drag reduction even with random distribution of those V-shaped protrusion.

• Wind and Structures
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• v.15 no.5
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• pp.423-439
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• 2012

Three common medium- rise building forms were physically tested to study their overall wind induced structural response. Emphasis was placed on the torsional response and its correlation with other peak responses. A higher correlation was found between the peak responses than between the general fluctuating parts of the signals. This suggests a common mechanism causing the peak event, and that this mechanism is potentially different to the mechanism causing the general load fluctuations. The measurements show that about 80% of the peak overall torsion occur simultaneously with the peak overall along wind drag for some generic building shapes. However, the peak torsional response occurs simultaneously with only 30%-40% of the peak overall drag for the rectangular model. These results emphasise the importance of load combinations for building design, which are often neglected in the design of medium sized rigid buildings for which the along-wind drag is dominant. Current design wind loading standards from around the world were evaluated against the results to establish their adequacy for building design incorporating wind-induced torsion effects. Although torsion is frequently neglected, for some structural systems it may become more important.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.23-31
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• 2010

The flow around a remotely-operated vehicle (ROV) has been investigated numerically to improve the resistant performance by modifying the hull form of the ROV. In the case of the base hull form considered in this study, form drag rather than friction drag was the dominant component of total drag. Subsequently, the surfaces that were most susceptible to local pressure effects were modified to give them a more streamlined shape. Eleven different hull forms were chosen to undergo surface modification for drag reduction. In addition, four different boat-tail appendages with different slant angles were installed at the stern to reduce the wake vortices that are induced by the local regions of very low pressure. Consequently, a total of 11 different hull forms for drag reduction were considered. The final hull form, which combined the hull for which surface modification resulted in the lowest drag with a boat-tail appendage with a 15-degree slant angle, resulted in a drag reduction of 20%.

• Journal of the Korean Institute of Gas
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• v.20 no.2
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• pp.23-29
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• 2016

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift and drag fluctuation over the fin tube was investigated. The derived nondimensional lift PSD was compared with the results of the previous experimental studies and the characteristics of lift and drag PSD over a single fin tube was established from the present CFD study.

• Journal of the Korean Institute of Gas
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• v.19 no.4
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• pp.35-40
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift and drag fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift and drag PSD over a single circular cylinder was established from the present CFD study.

• Journal of Mechanical Science and Technology
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• v.20 no.7
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• pp.1051-1058
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• 2006

The steady aerodynamic characteristics of a wing flying over a channel are investigated using a boundary-element method. The present method is validated by comparing the computed results with the measured data. Compared with a flat ground surface, the channel fence augmented the lift increase and induced drag reduction. When the fence is lower than the wing height, the gap between the wingtip and the fence does not affect the aerodynamic characteristics of the wing much. When the fence is higher than the wing height, the close gap increased the lift. The induced drag is reduced when the wing is placed near the ground or at the same height as the fence. It is believed that present results can be used in the conceptual design of the high-speed ground transporters flying over the channel.

• Wind and Structures
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• v.4 no.2
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• pp.163-176
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• 2001

Two 12 m high tubular steel lighting columns have been instrumented to determine the wind-induced fatigue loading experienced by such columns. Each column supported a single luminaire mounted on a 0.5 m long bracket. One column was planted in soil, and the other bolted through a welded baseplate to a substantial concrete base. The columns were strain gauged just above the shoulder weld which connected the main shaft to the larger base tube. Forced vibration tests were undertaken to determine the natural frequencies and damping of the columns. Extensive recordings were made of response to winds with speeds from 4 m/s to 17 m/s. Selected records were analysed to obtain stress cycle counts and fatigue lives. Mean drag coefficients were also derived from the strain data to investigate experimentally the effect of Reynolds Number.