• Wind and Structures
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• 제26권4호
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• pp.253-266
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• 2018

In this paper, the aerodynamic performance of two new cable surfaces with concave fillets (strakes) is examined and compared to plain, dimpled and helically filleted surfaces. To this end, an extensive wind-tunnel campaign was undertaken. Different samples with different concave fillet heights for both new surfaces were tested and compared to traditional surfaces in terms of aerodynamic forces (i.e. drag and lift reduction) and rain-rivulet suppression. Furthermore, flow visualization tests were performed to investigate the flow separation mechanism induced by the presence of the concave fillet and its relation to the aerodynamic forces. Both new cable surfaces outperformed the traditional surfaces in terms of rain-rivulet suppression thanks to the ability of the concave shape of the fillet to act as a ramp for the incoming rain-rivulet. Furthermore, both new surfaces with the lowest tested fillet height were found to have drag coefficients in the supercritical Reynolds range that compare favorably to existing cable surfaces, with an early suppression of vortex shedding.

• Advances in aircraft and spacecraft science
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• 제1권1호
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• pp.27-41
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• 2014

An active flow control technique based on "smart-tabs" is proposed to delay flow separation on a circular cylinder. The actuators are retractable and orientable multilayer piezoelectric tabs which protrude perpendicularly from the model surface. They are mounted along the spanwise direction with constant spacing. The effectiveness of the control was tested in pre-critical and in post-critical regime by evaluating the effects of several control parameters of the tabs like frequency, amplitude, height, angular position and plate incidence with respect to the local flow. Measurements of the mean static pressure distribution around the cylinder were used to estimate the pressure drag coefficient. The maximum drag reduction achieved in the pre-critical regime was of the order of 30%, whereas in the post-critical regime was about 10%, 3% of which due to active forcing. Furthermore, pressure fluctuation measurements were performed and spectral analysis indicated an almost complete suppression of the vortex shedding in active forcing conditions.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2011년도 추계학술논문집 2부
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• pp.600-603
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• 2011

볼텍스 튜브는 고압의 가스를 이용하여 고온 가스와 저온 가스로 에너지를 분리하거나 입자상 물질의 분리에 사용 할 수 있는 장치이다. 본 연구에서는 컨버징튜브($D_{in}$=10mm, $D_{out}$=6mm)와 다이버징튜브($D_{in}$=6mm, $D_{out}$=10mm)의 성능을 비교, 분석하였다. 기존에 제작된 베이스튜브(D=6, 10mm)를 기준으로 하여 컨버징 튜브와 다이버징 튜브의 에너지분리 특성 실험을 수행하였다. 결과적으로 튜브의 입구직경보다 출구직경이 커지는 다이버징 튜브에서 우수한 성능을 확인 할 수 있었다.

• International Journal of Fluid Machinery and Systems
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• 제6권1호
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• pp.18-24
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• 2013

In order to apply the design method of diagonal flow fan based on axial flow design to the design of radial-outflow type diagonal flow fan which has lower specific speed of 600-700 [$min^{-1}$, $m^3/min$, m], radial-outflow type diagonal flow fan which specific speed was 670 [$min^{-1}$, $m^3/min$, m] was designed by a quasi three-dimensional design method. Experimental investigations were conducted by fan characteristics test, flow surveys by a five-hole probe and a hot wire probe. Fan characteristics test agreed well with the design values. In the flow survey at rotor outlet, the characteristic region was observed. Two flow phenomena are considered as the cause of the characteristic region, one is tip leakage vortex near rotor tip and another is pressure surface separation on the rotor blade.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.316-320
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• 2008

In this paper, the near wake of stationary and transversely oscillating square section cylinders with different corner radii are studied by numerical method to investigate the influence of corner radius. Six models R/D=0,0.1,0.2,0.3,0.4,0.5 (R is the corner radius and D is the characteristic dimension of the body) were studied. It was found that the corner radius of square cylinder significantly influences the flow features around the body both in stationary and oscillating conditions. Results indicate that, as R/D ratio increases, the Strouhal number increases and the separation point decrease for the stationary and oscillating cases.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.11-12
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• 2006

We conducted a direct numerical simulation (DNS) to establish database for the purpose of improvement of practical method which is applicable to cavitating turbulent flows. Cavitations caused by spanwise and streamwise vortices, which are typical features in high shear layer, is represented by a simple model and interaction between vortices and cavities is reproduced. The qualitative agreement between computation and experiment are reasonable. Cavities due to streamwise vortices in a shear layer seem to attenuate turbulent eddies.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.316-320
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• 2008

In this paper, the near wake of stationary and transversely oscillating square section cylinders with different corner radii are studied by numerical method to investigate the influence of corner radius. Six models R/D=0,0.1,0.2,0.3,0.4,0.5 (R is the corner radius and D is the characteristic dimension of the body) were studied. It was found that the corner radius of square cylinder significantly influences the flow features around the body both in stationary and oscillating conditions. Results indicate that, as R/D ratio increases, the Strouhal number increases and the separation point decrease for the stationary and oscillating cases.

• 한국전산유체공학회지
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• 제15권4호
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.848-851
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• 2003

In this paper, a separating system for used CRT recycling is presented. Depend on manufacturer CRTs has small differences in dimension for the same model, but the dimensions of the panel are nearly same. To simplifying configuration of the system, we developed CRT fixing pallets for every model of CRT. The height of cutting position for every model of CRT will be same. The cutting machine has two rotating arm and use metal-bond type diamond cutting wheel. Instead of water, two vortex tube type air-coolers are used for the cooling of cutter. Workers in recycling factory are generally old people. Therefore, control program should be easy to use and operate. Thus we developed GUI with very simple interface.

• Wind and Structures
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• 제19권1호
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• pp.59-73
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• 2014

This paper presents the results of wind tunnel studies and numerical studies on a '+' plan shaped tall building. The experiment was carried out in an open circuit wind tunnel on a 1:300 scale rigid model. The mean wind pressure coefficients on all the surfaces were studied for wind incidence angle of $0^{\circ}$ and $45^{\circ}$. Certain faces were subjected to peculiar pressure distribution due to irregular formation of eddies caused by the separation of wind flow. Moreover, commercial CFD packages of ANSYS were used to demonstrate the flow pattern around the model and pressure distribution on various faces. k-${\varepsilon}$ and SST viscosity models were used for numerical study to simulate the wind flow. Although there are some differences on certain wall faces, the numerical result is having a good agreement with the experimental results for both wind incidence angle.