• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제27권4호
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• pp.232-244
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• 2023

The unsteady dynamics of the starting flow of a flat plate is studied by using a vortex shedding model. The model describes the body and separated vortex from the trailing edge of the plate by vortex sheets, retaining a singularity at the leading edge. The model is applied to simulate the flow of an accelerated plate for small angles of attack. For numerical computations, we take two representative cases of the translational velocity of a plate: impulsive translation and uniform acceleration. The model successfully demonstrates the formation of wakes shed from the plate. The wake behind the plate is stronger for a larger angle of attack. Predictions for the lifting force from the model are in agreement with results of Navier-Stokes simulations.

• 대한기계학회논문집
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• 제8권1호
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• pp.1-9
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• 1984

In the utilization of solar energy most often a flat solar collector is used for solar heating, system. Since solar energy is absorbed through this solar collector, it is considered to be a most important part in the whole solar heating system. The purpose of the present investigation is to evaluate the influence of varying design parameters for thermal performances of flat-plate solar collector. By analysing these parameters, optimum design of solar collector would become possible. Specification of the existing solar collector are utilized in calculation as a starting point. Analysis is carried out numerically for "Unit Solar Collector" which is composed of fin and tube. Among design parameters. such parameters as mass flow rate per unit area, tube spacing and fin thickness are selected as variables in the computer simulation model. Results are presented for thermal performances of flat-plate solar collector for each important design parameters, so that predictions become possible through numerical analysis without performing experiments whenever it is required. required.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.106-110
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• 2004

Generally, flow around a bluff body such as a circular cylinder is complicated compared with that around a streamlined body because of the existence of separated shear layers. Long bluff body such as a flat blunt plate is more complicated than short bluff body, because of separated-and-reattaching flow on the after bodies.(omitted)

• 한국입자에어로졸학회지
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• 제9권2호
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• pp.79-87
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• 2013

In this study, the characteristics of turbulent flow and collection efficiency for an one-stage electrostatic precipitator(ESP) with slit type collecting electrode for urban railway underground tunnels were obtained using computational fluid dynamics(CFD) commercial code FLUENT 6.3 and lab-scale experiments. The electrostatic precipitator was operated under high gas velocity(3~12m/s). Five different designs of collecting electrode, flat plate-type and a slit-type of 3mm, 5mm, 7mm and 10mm slit width and four various gas velocity(3, 6, 9, and 12m/s) were used and applied. A standard k-${\varepsilon}$ model in CFD commercial code FLUENT 6.3 was used for flow simulation. The flow simulation results showed that the turbulent intensity of flat plate-type was higher than slit-type under all gas velocity conditions and also the turbulent intensity of flat plate-type was increased continuously, but in case of slit-type was maintained at constant range. And, the turbulent intensity was decreased according to increasing of slit width. The experimental results showed that the collection efficiency of slit-type was higher than flat plate-type under all gas velocity conditions. And, over 6m/s gas velocity condition, the collection efficiency of 5mm and 7mm was highest, when compared to 3mm and 10mm.

• 대한기계학회논문집B
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• 제24권7호
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• pp.976-983
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angle of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder due to the presence of a ground plate nearby.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.879-887
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• 2003

The flow in a parallel walled test channel, when obstructed with a geometry at the entrance, can be forward, reverse and stagnant depending on the position of the obstruction. This interesting flow phenomenon has potential benefit in the control of energy and various flows in the process industry In this experiment, the flat plate obstruction geometry was used as an obstruction at the entry of the test channel. The parameters that influence the flow inside and around the test channel were the gap (g) between the test channel and the obstruction geometry, the length (L) of the test channel and the Reynolds number (Re). The effect of the gap to channel width ratio (g/w) on the magnitude of the velocity ratio (V$\_$i/ / V$\_$o/ : velocity inside/ velocity outside the test channel) was investigated for a range of Reynolds numbers. The maximum reverse flow observed was nearly 20% to 60% of the outside velocity for Reynolds number ranging from 1000 to 9000 at g/w ratio of 1.5. The maximum forward velocity inside the test channel was found 80% of the outside velocity at higher g/w ratio of 8. The effect of the test channel length on the velocity ratio was investigated for different g/w ratios and a fixed Reynolds number of 4000. The influence of the Reynolds number on the velocity ratio is also discussed and presented for different gap to width ratio (g/w). The flow visualisation photographs showing fluid motion inside and around the test channel are also presented and discussed.

• 멤브레인
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• 제8권2호
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• pp.102-108
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• 1998

본 연구는 Si 미립자를 함유한 반도체 세정폐수의 평판막을 이용한 한외여과특성을 검토하였다. 평판막의 투과유속은 시간이 경과함에 따라 점차 감소하는 경향을 나타냈으며, 이현상은 막표면에 형성된 케익층의 증가 및 기공막힘에 기인한다. 흐름형태에 따른 투과유속은 cross flow가 dead-end flow의 약 1.4배 높았다. Si 미립자에 의한 막오염을 제거하는데는 역세법이 sweeping법 보다 우수하였다. 막오염으로 인한 투과유속의 감소는 질소가스로 역세척하여 초기투과유속의 약 85% 정도 회복되었다. 평판막을 이용한 cross flow 공정의 용질배제율은 약 90%였으며, 투과수증의 Si 미립자의 크기는 평균 70 nm였다.

• 한국가시화정보학회지
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• 제16권3호
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• pp.16-25
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• 2018

PIV experiments were carried out to visualize the velocity distribution of the sweeping jet impinging onto a flat plate and kinematic behavior of the jet from the fluidic oscillator. Two parameters such as four different Re cases and four different jet-to-wall distances were examined. Time-resolved two dimensional PIV measurements were performed for both streamwise and normal planes respect to the jet axis. Ensemble averaged and phase averaged velocity fields were obtained for the tested range of parameters. The sweeping frequency of the jet increases linearly with increase of Re. The kinetic energy of the sweeping jet decreases as the distance from the jet to the impinging plate increases. In addition, turbulence flow is generated due to the swinging motion of sweeping jet, and various vortices such as primary and secondary vortex are observed near the impinging wall.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1998년도 제10회 학술강연회논문집
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• pp.15-15
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• 1998

The problem of the impingement of a sonic or a supersonic jet on a flat surface has not only wide applications but has also interesting and very complex flow phenomena. The main applications of this impinging jet include prediction of solid surface erosion, design of launcher systems, stage separation of multi-stage rocket system, V/STOL operations, thermal spray system, and manufacturing technologies of materials. Much have been learned about the supersonic impinging jet flow field but many fundamental questions have not been answered satisfactorily. The problem encompasses many facets of fluid dynamics which, in combination, present the compressibility effect and the viscous-inviscid interaction, coupled with flow separation and reattachment. What is more, there are many flow parameters that have on the impinging jet flow field, for example, Mach number, Reynolds number, pressure ratio, distance between the nozzle exit and flat plate, jet shock structure, nozzle diameter and etc. Thus the existing data on the supersonic impinging jet flow present considerable disagreement in which quantitative comparison between one result and another is often impossible.

• 한국분무공학회지
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• 제9권4호
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• pp.53-66
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• 2004

An experimental study was carried out in order to investigate the influence of flow conditions on a boundary layer in the near-wake of a flat plate. The flow conditions in the vicinity of the trailing edge that is influenced by upstream condition history are an essential factor that determines the physical characteristics of a near-wake. Tripping wires attached at various positions were selected to change flow conditions of a boundary layer. The flows such as laminar, transitional, and turbulent boundary layer at 0.98C from the leading edge are imposed in order to investigate the evolution of symmetric and asymmetric wake. An x-type hot-wire probe(55P61) is employed to measure at 8 stations in the near-wake. Test results show that the near-wake for the case of a turbulent boundary layer is relatively insensitive to instability after separating at the trailing edge, and Reynolds shear stress in the near-wake for the case of a turbulent boundary layer collapses due to turbulent kinetic energy.