• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.89-95
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• 2000

To obtain an exact flow loss in piping systems is very important in the face of efficiency anticipation and work control of plant. The object of this study is to get the flow loss through the experiment for sudden expansion and contraction part of circular pipe nozzle. The experiment in this study is performed after getting the flow loss factor for sudden expansion and contraction through preliminary experiments. It is confirmed that the results of this study agreed with the approximated equation of Ikeda and Matsuo. It is proved that flow loss factor ${\zeta}_3$for sudden expansion and contraction part of circular pipe is dependent on $L/D_1$in these experimental conditions.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.272-281
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• 2009

The effect of swirl on the flow characteristics in a sudden expansion tube was examined experimentally by using 3D PIV(particle image velocimetry) to capture the velocity profiles. The swirling flow of water through a sudden 1:2 axisymmetric expansion has previously been studied experimentally within a horizontal round tube. A kind of tangential slot is used as a swirl generator for swirling flow and a honey comb is used for without swirl flow. The work with the swirl and without swirl results are compared to each other at the same Reynolds number. Liquid crystal was employed to measure temperature profiles and heating coil used for heat transfer with and without swirl flow. And then the Nusselt number ratoes(Nu/Nudb) are calculated along the test section.

• 대한기계학회논문집
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• 제18권12호
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• pp.3335-3344
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• 1994

The initial flow characteristics of the turbulent circular jet discharging into the sudden expansion pipes have been investigated by the hot wire anemometry. Evolutions of similarity, centerline behavior, jet boundary and typical turbulent quantities were looked into for the expansion ratios. The results show that the spreading rates of discharging jet seem not to be dependent of the expansion ratio and that the velocity profiles in the radial directions exhibit the similarity in the regions, 2-5d, 2-6d and 3-8d for the corresponding expansion rations of 2, 3 and 5, respectively. With the increase of expansion ratio the centerline velocity decays rather slowly. The anisotropic behaviors of the discharging jets into the sudden expansion pipe look stronger than those of the free jet.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.33-38
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• 2001

Bifurcation of unstable symmetric flow patterns to stable asymmetric ones in laminar sudden-expansion flow has been numerically investigated. Computations were carried out for an expansion ratio of 3 and over a range of the flow Reynolds numbers by using numerical methods of second-order time accuracy and a fractional-step method that guarantees divergence-free flowfields at all times. The critical Reynolds number above which bifurcation of pitchfork type to asymmetric flow pattern takes place is lower in a flow with a higher expansion ratio, in agreement with the previously reported results. The bifurcation diagrams show that the bifurcation takes place at a Reynolds number, $Re_c = 86.3$, higher than the value that has been reported. The lower critical Reynolds number may be due to deficiencies in their computations which employed SIMPLE-type relaxation methods rather than the initial-value approach of the present study. Characteristics of the flow development during the transition to asymmetric stable flow have been investigated by using spectral analysis of the velocity signals obtained by the simulations.

• 대한의용생체공학회:의공학회지
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• 제11권2호
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• pp.233-242
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• 1990

In the current flow visualization studies, the role of non-Newtonian characteristics (such as shearra to dependent viscosity and viscoelasticity ) on flow behavior across the sudden ex- pansion step in a circular pipe as a model for blood flow experiments is investigated over a wide range of Reynolds numbers. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10~35, 000 based on the inlet. diameter. The reattachment longuEs for the viscoelastic fluids in the lami- nar flow regime are found to be much shorter than those for the Newtonian fluid. In addition it decreases significantly with increasing concentration of viscoelastic fluids at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids Is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting In 25 and 28 step-height dis- tances for 500 and 1, 000 lpm ployacrylamide solutions, respectively. This may be due to the fact that the elasticity in pobacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pips flow.

• Journal of Advanced Marine Engineering and Technology
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• 제35권4호
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• pp.468-474
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• 2011

급확대 축소 채널에 설치된 배플 주위의 유동장을 PIV기법으로 계측하고, 배플의 높이 변화에 따른 영향을 평가하였다. 유입유속과 배플 높이는 배플 후방의 재순환흐름에 크기와 유동패턴 및 배플의 상부를 지나는 수력점프 영역의 크기에 상호 영향을 준다. 레이놀즈수 $Re=4{\times}10^3$의 경우 유입유속의 증가에도 유속이 낮아지는 배플의 임계높이는 h/H=1.6전후로 추정된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.68-73
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• 1996

The full incompressible Navier-Stokes equations are numerically integrated to solve the unsteady channel flow using a new numerical scheme of second-order accuracy developed by the authors. It is well known that in spite of the symmetry in the boundary condition and geometry, asymmetry can develop with time-dependency in a channel with sudden expansion. The instability of the shear flow and the cross-channel pressure contribute to such asymmetric flow. In this paper, we successfully generated a channel flow in which vortex waves were propagated downstream due to the harmonically oscillating inlet flow. The structure of the eddies and wall vorticity are parametrically investigated.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.766-774
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• 2017

알루미늄과 같은 금속분말을 연료로 사용하는 추진체의 연료공급장치에 있어, 원통형 공급관 내부를 이동하는 분말이 연소기로 진입하면서 발생되는 분말의 급확대부 영역에서의 확산현상을 해석하기 위해 컴퓨터 소프트웨어를 개발하였다. 플러그 유동형태의 입자집단운동을 기술하기 위해서 일종의 Lagrangian기법이며 난류속도변동 조건을 만족하는 개별입자추적법을 도입하였다. 여기에 재순환 영역에서 유체의 방향전환을 증진시키기 위해 기하학적 유동 구조에 입각한 반경방향 속도성분을 추가시켰다. 속도 추가성분의 유무에 따른 급확대부 재부착점 부근에서의 입자 속도분포 수치해석 결과를 기존의 실험결과와 비교하였다.

• 대한설비공학회지:설비저널
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• 제13권1호
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• pp.5-13
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• 1984

This analysis of numerical procedure is prediction of laminar flow and heat transfer at two dimension and steady flow in asymmetric sudden expansion channel. At former study, to analyse the flows with separation, the full Navier-Stokes equation is used, but there are many difficulties to analyse, and although significant progress has been made in the development of efficient computational methods for the Navier-Stokes equations, very large computation times are still required. In case of reward-facing flow, boundary-layer equation is used instead of full Navier-Stokes equation to analyse velocity fields, and result of this numerical analysis is good agreement with the given experimental study. In this case, since the computer time required for the boundary-layer calculation is an order of magnitude less than required for the solution of the full Navier-Stokes equation, this boundary-layer model provides a good approximate solution.

• 오토저널
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• 제15권1호
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• pp.45-54
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• 1993

The reattachment lengths of the Non-Newtonian fluid are investigated in the sudden expansion pipes whose ratios are 2.316 and 3.368, and the range of the Reynolds numbers is 100-30000. The reattachment lengths for the viscoelastic fluid in the laminar flow region are found to be much shorter than those of the Newtonian fluid, and decrease significantly with the increase of the concentration of viscoelastic fluid is two or three times longer than those of water, and gradually increases with the increase of the concentration of viscoelastic fluid.