• 한국가시화정보학회지
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• 제9권1호
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• pp.20-28
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• 2011

An experimental assessment has been made of the drag reducing efficiency of the outer-layer vertical blades, which were first devised by Hutchins. The drag reduction efficiency of the blades was reported to reach as much as 30%. However, the drag reduction efficiency was quantified only in terms of the reduction in the local skin-friction coefficient. In the present study, a series of drag force measurements in towing tank has been performed toward the assessments of the total drag reduction efficiency of the outer-layer vertical blades. A maximum 9.6% of reduction of total drag was achieved. The scale of blade geometry is found to be weakly correlated with outer variable of boundary layer. In addition, detailed flow field measurements have been performed using 2-D time resolved PIV with a view to enabling the identification of drag reduction mechanism.

• Wind and Structures
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• 제25권3호
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• pp.301-328
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• 2017

Multivariate fluctuating pressures acting on a 2:1 rectangular section (2-D) with dimensions of 9 cm by 4.5 cm has been studied using wind tunnel experiments under uniform and smooth flow condition for various angles of wind incidence. Based on the variation of mean pressure coefficient distributions along the circumference of the rectangular section with angle of wind incidence, and with the aid of skin friction coefficients, three distinct flow regimes with two transition regimes have been identified. Further, variations of mean drag and lift coefficients, Strouhal number with angles of wind incidence have been studied. The applicability of Universal Strouhal number based on vortex street similarity of wakes in bluff bodies to the 2:1 rectangular section has been studied for different angles of wind incidence. The spatio-temporal correlation features of the measured pressure data have been studied using Proper Orthogonal Decomposition (POD) technique. The contribution of individual POD modes to the aerodynamic force components, viz, drag and lift, have been studied. It has been demonstrated that individual POD modes can be associated to different physical phenomena, which contribute to the overall aerodynamic forces.

• Wind and Structures
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• 제20권3호
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• pp.449-468
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• 2015

Current wind-resistance designs of large-scale indirect dry cooling towers (IDCTs) exclude an important factor: the influence of the ventilation rate for radiator shutter on wind loads on the outer surfaces of the tower shell. More seemingly overlooked aspects are the effects of various ventilation rates on the wind pressure distribution on the tower surfaces of two IDCTs, and the feature of the flow field around them. In order to investigate the effects of the radiator shutter ventilation rates on the aerodynamic interference between IDCTs, this paper established the numerical wind tunnel model based on the Computational Fluid Dynamic (CFD) technology, and analyzed the influences of various radiator shutter ventilation rates on the aerodynamic loads acting upon a single and two extra-large IDCTs during building, installation, and operation stages. Through the comparison with the results of physical wind tunnel test and different design codes, the results indicated that: the influence of the ventilation rate on the flow field and shape coefficients on the outer surface of a single IDCT is weak, and the curve of mean shape coefficients is close to the reference curve provided by the current design code. In a two-tower combination, the ventilation rate significantly affects the downwind surface of the front tower and the upwind surface of the back tower, and the larger positive pressure shifts down along the upwind surface of the back tower as the ventilation rate increases. The ventilation rate significantly influences the drag force coefficient of the back tower in a two-tower combination, the drag force coefficient increases with the ventilation rate and reaches the maximum in a building status of full ventilation, and the maximum drag coefficient is 11% greater than that with complete closure.

• 한국항해항만학회지
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• 제35권3호
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• pp.197-204
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• 2011

회류수조에서의 대각도 정적(static) 모형실험을 통해 Manta형 무인잠수체에 작용하는 동유체력을 측정하였으며, 동유체력에 미치는 Reynolds수의 영향을 고찰하였다. 이를 위해 동유체력을 cross-flow drag과 양력(lift force)으로 성분 분석을 하였으며, 양력 성분에는 Reynolds수의 영향을 무시하고, cross-flow drag 성분에만 Reynolds수의 영향을 고려하였다. 그 후 이들 두 성분을 다시 합성함으로써 실물 무인잠수정에 작용하는 동유체력의 추정 기법을 제시하였다.

• 한국항만학회지
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• 제10권1호
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• pp.15-23
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• 1996

In this paper, the numerical model to analyze the wave absorbing performance of upright perforated plates is developed under the linear potential theory. If the drag force is dominent to the inertia force in passing perforated plate, the characteristics of perforated plates are determined by a nondimensionlized real-value of G or a length scaled real-value of a. The parameters (G,a), which depend on the drag coefficient, porosity and local shape of plates, can be readily obtained by simple experiments. We investigated the reflection coefficients over a wide frequency range according to the arrays of perforated plates with different values of G and a. We found that the wave absorbing system using the arrays of upright perforated plates is sufficient to install in the ocean engineering basin.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1175-1182
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• 2002

The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.392-394
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• 2011

This paper is concerned about the hydrodynamic coefficients of hydrofoil. We discretized the incompressible Navier-Stokes equation with second order Runge-kutta for the time in the second order compact scheme for the spatial. The three-dimensional CFD code based on hybrid mesh on the finite volume method is used to simulate flow around NACA series foils. Lift and drag coefficient is calculated for several NACA series foils using different mesh types. Our aim is to obtain the lift and drag coefficient to evaluate the robustness of the solver and to shaw the advantage of using trim tab at the trailing edge. It concludes with a discussion of results and recommendations for future work.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.71-74
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• 2008

This paper aims at studying the key design elements for the optimal ventilation system design, developing the design models and suggesting the design guidelines. The key elements include the basic exhaust emission rate, wall friction coefficient, vehicle drag coefficient and slip streaming effect, jet fan operating efficiency, natural ventilation force and installation scheme for jet fans and ventilation monitors in tunnel. The design models developed in this study are one-dimensional ventilation simulator to analyze the air flow, pressure profile and pollutant dispersion inside and outside tunnel, expert model to choose the optimal ventilation method, and the ventilation characteristic chart to evaluate the preliminary ventilation system. The study results are reflected in the design guideline for road tunnel ventilation system.

• 대한조선학회논문집
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• 제57권2호
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• pp.96-103
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• 2020

The new geometric disturbance is proposed to control the flow around the bluff body. The new geometry is characterized by the variable pitch which is applied on the Helically Elliptic Twisted (HET) cylinder. The performance of the HTE geometry as a biomimetic passive flow control was confirmed by Jung and Yoon (2014). The Large Eddy Simulation (LES) is used for the evaluation of the flow control performance of the Variable Pitch HTE (VPHTE) cylinder at Reynolds number (Re) of 3000 corresponding to the subcritical regime. The circular and HTE cylinders are also considered to compare the performance of the VPHTE cylinder at the same Re. The VPHTE cylinder gives the smallest values of the force coefficients than the circular and HTE cylinders. The drag and lift coefficients of the VPHTE cylinder are about 15.2% and 94.0% lower than those of the circular cylinder, respectively. Especially, the VPHTE cylinder achieves about 2.3% and 30.0% reduction of the drag coefficient and the root mean square of the lift coefficient than the HTE cylinder, respectively. Furthermore, The VPHTE cylinder forms more elongated and stabilized separated shear layer than the circular cylinder, which supports the reduction of the force coefficients.

• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.575-579
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• 2015

본 연구에서는 스파이럴 보강을 한 원형 실린더 주위의 유동를 분석하였다. 이를 위해 스파이럴 보강 부분을 사각형 부착물로 분리해서 나타내었다. EDISON_CFD의 가상 경계법을 이용하여 원형 실린더와 부착물 주위의 유동 현상을 해석하였다. 부착물의 두께와 각도를 다르게 하여 각각의 공력 계수와 총 합력을 구하고 이에 따른 특성을 분석하였다.