• 한국전산유체공학회지
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• 제19권1호
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• pp.73-79
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• 2014

Three-dimensional turbulent flows of a distribution manifold are studied by a turbulence model. To investigate the geometrical effects of the manifold, the length and area of exit port are changed. From the results, flow structures related to the outflow uniformity are examined and the deparure angles are obtained. The exit configuration depending on the departure angle has advantages to the outflow uniformity. That is, the decreased exit area in the streamwise direction improves the uniformity of exit flow. For the uniform effusion, the change of exit port by departure angle is more effective them the change of exit area.

• Bulletin of the Korean Chemical Society
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• 제16권11호
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• pp.1023-1027
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• 1995

A comparative study of different torches in the Microwave Induced Plasma is reported. Three types of torches that have been used in this area are characterized and compared with each other. Especially, recently developed laminar flow torches have been optimized in design and analytical performances. The ratio of inner to outer tubes is found to be the most important parameter. As inner tube size increases, recirculating region also increases and consequently, sensitivity becomes better. An optimized laminar flow torch has been coupled to a gas chromatography and examined for halogen compounds. Detection limits are 25 pg s-1 for Cl and 12 pg s-1 for Br. These values are improved over the conventional laminar flow torch.

• 한국수자원학회논문집
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• 제40권3호
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• pp.277-286
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• 2007

사다리꼴단면을 가진 광정횡월류위어에서의 흐름특성을 3차원 수치모의를 통해 분석하였다. 본 연구결과， 본류 수로의 푸르드수가 증가함에 따라 월류유량비와 횡월류 유량계수는 감소하는 경향을 보였다. 그리고 횡월류 유량이 증가하면서 월류부 하류 수로의 주흐름구간은 축소되며，횡윌류위어의 대안 측에 형성되는 재순환영역의 크기는 증가하는 양상을 보였다. 횡월류위어 측에서의 주흐름방향 수위분포는 위어 시점부에서 급격히 하강하여 점차 증가하다 위어 종점부에서 급격히 상승했다 하강하는 양상을 보이는데, 위어 종점부에서 수위가 급히 상승하는 원인은 위어의 종점부가 흐름의 장애물로 작용하기 때문이다.

• 한국전산유체공학회지
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• 제7권4호
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• pp.35-41
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• 2002

The projectile afterbodies for zero-lift drag reduction has been analyzed using the Navier-Stokes equations with the κ-εturbidence model. The numerical method of a second order upwind scheme has been used on an unstructured adaptive grid system. Base drag reduction methods that have been found effective on axisymmetric bodies are boattailing, base bleed, base combustion, locked vortex afterbodies and multistep afterbodies. In this paper, turbulence flow and pressure charateristics have been studied for geometries of multistep afterbodies. The important geometrical and flow parameters relevant to the design of such afterbodies have been identified by step number, length and height. The flow over multistep aftoerbodies or base have many kinds of compressible flow characteristics including expansion waves at the trailing edge, recompression waves, separation and recirculating flow in the base region, shear flow and wake flow. The numerical results have been compared and analyzed with the experimental data. The flow characteristics have been clearly shown.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.703-704
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• 2002

The two major problems related to the blood flow in a floating type polymer valve are thrombus formation and hemolysis. It is well known that the shear stress in the fluid and flow separation around the valve are blamed for such disastrous phenomena. In this viewpoint, through study of the flow field around the valve is imperative to improve design of the valve. The aim of this study is to investigate the fluid flow around a floating type polymer valve. The numerical method employed in this study is the finite element software called ADINA. Incompressible viscous flow is assumed for blood using the assumption of Newtonian fluid. In this study, two prominent features of the axisymmetric flow around the floating type polymer valve are observed: jet-like flows observed near the gap between the conduit and the valve, and recirculating flow downstream of the valve. We also provided a detailed description of shear stress field according to the variation of flow conditions. The shear stress in fluid has its maximum value near the gap between the valve and the conduit.

• 대한기계학회논문집B
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• 제39권8호
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• pp.669-675
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• 2015

자동차용 터보차저 원심압축기의 재순환케이싱처리(RCT)부의 높이변화가 압축기의 성능에 미치는 영향이 조사되었다. 연구대상 RCT 부의 높이는 1.2mm, 1.5mm, 1.8mm 의 세가지이며, 회전수 범위는 90,000 - 150,000 rpm, 유량 범위는 0.015 kg/s - 0.08 kg/s 이다. 전압력비와 등엔트로피 효율 비교 결과, 본 수치계산은 실제압축기의 성능 제원과 최대오차 0.7%의 범위 내에서 잘 일치하였다. 해석결과, RCT 부 높이 1.2mm, 1.8mm, 1.5mm 순서로 균일 압력분포, 높은 압력비, 넓은 작동범위를 얻었다. 이들 세가지 경우 모두, 회전수가 증가할수록 이들의 압력비는 높아지나 운전범위는 좁아지는 전형적인 압축기 맵의 특성을 보여주었다.

• 대한기계학회논문집B
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• 제21권1호
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• pp.49-56
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• 1997

Heat-transfer enhancement is seeked through modifications of fin surface. Real life plate-fin heat exchangers have complex three-dimensional geometries. Fins can have arrays of dimples and are attached to rows of penetrating tubes. To isolate the effect of surface modification, we model the real flow by a two-dimensional channel flow with a dimple on one side. The flow is analysed by solving the incompressible Navier-Stokes equation by a finite volume method on a generalized boundary-fitted coordinate. Results show a trapped vortex inside the dimple for all cases computed. Local maximum of Nusselt number occurs near the downstream end of the dimple, due to such a vortex. Location of the vortex does not change with respect to the wall temperature change, but moved downstream when Reynolds number increases. This, together with the results that in all cases vortex core is somewhat downstream of the dimple center, suggests that the mean flow above continuously feeds the kinetic energy to the recirculating flow. Heat transfer enhancement and pressure losses are studied through analysing the relevant dimensionless parameters like, Nusselt number and friction factor. In all cases computed, dimpled channel flow experiences less pressure loss than two-dimensional Poiseuille flow.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제44회 KOSCO SYMPOSIUM 초록집
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• pp.201-202
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• 2012

The isothermal flow structure and mixing characteristics of a hybrid/dual swirl jet combustor for micro-gas turbine were numerically investigated. Location of pilot nozzle, angle and direction of swirl vane were varied as main parameters with constant fuel flow rates for each nozzle. As a result, the variation in location of pilot nozzle resulted in significant change in turbulent flow field near burner exit, in particular, center toroidal recirculation zone (CTRZ) as well as turbulent intensity, and thus flame stability and emission characteristics might be significantly changed. The swirl angle of $45^{\circ}$ provided similar recirculating flow patterns in a wide range of equivalence ratio (0.5~1.0). Compared to the co-swirl flow, the counter-swirl flow leaded to the reduction in CTRZ and fuel-air mixing near the burner exit and a weak interaction between the pilot partially premixed flame and the lean premixed flame. With the comparison of experimental results, it was confirmed that the case of co-swirl flow and swirl $angle=45^{\circ}$ would provided an optimized combustor performance in terms of flame stability and pollutant emissions.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.232-237
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• 1991

Digital Variable Structure Controller(DVSC) is proposed to control variable speed recirculating pump for hot-water heating control system. In this study, nonlinear sliding line is used beyond output error boundary layer and PID sliding line is used within the layer. For long dead time compensation, constraint is added to Smith predictor algorithm. Steady state error is eliminated by using the proposed sliding line in spite of heating load change. By decreasing sampling time, good sliding motion is yielded but system output noise bv flow dynamics is amplified.

• Journal of Advanced Marine Engineering and Technology
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• 제28권1호
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• pp.124-135
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• 2004

An experimental study is performed turbulent flow behind a square cylinder by using 2-D PIV technique. The Reynolds number investigated are 10.000. 30.000 and 50,000. The mean velocity vector, time mean axial velocity turbulence intensity. kinetic energy and Reynolds shear stress behind the cylinder are measured, The numerical method used this study is a CFD code, STAR-CD. The numerical results are compared with these of experimental.