• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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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)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.1-9
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• 2002

Axisymmetric separated flows in a converging-diverging conical nozzle are investigated through numerical simulations for various pressure ratios. We employ AUSM scheme for spatial derivatives and Pulliam's 2nd order subiteration time stepping scheme for implicit time integration. Numerical results indicate that the separated flow structures are very complex when compared to the simple quasi-one dimensional flow. Depending on the pressure ratio, the flow within the nozzle is either separated or non-separated. Various separated flow patterns with distinctive features are illustrated and discussed in detail.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.68-72
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• 2006

Vertical fence has the coherent flow structure in front of the fence. In the present study, the wake change due to the flow separator in front of the vertical fence was experimentally investigated. Quantitative method was applied to study the separated shear flow field. The results show the flow separator changes the downstream shear flow and alters the curvature of separated shear layer As the freestream velocity increased, the reattachment length also increased.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.669-677
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• 2015

A mechanistic model for void fraction prediction with improved interfacial friction factor in nearly horizontal tubes has been proposed in connection with the development of a condensation model package for the passive auxiliary feedwater system of the Korean Advanced Power Reactor Plus. The model is based on two-phase momentum balance equations to cover various types of fluids, flow conditions, and inclination angles of the flow channel in a separated flow. The void fraction is calculated without any discontinuity at flow regime transitions by considering continuous changes of the interfacial geometric characteristics and interfacial friction factors across three typical separated flows, namely stratified-smooth, stratified-wavy, and annular flows. An evaluation of the proposed model against available experimental data covering various types of fluids and flow regimes showed a satisfactory agreement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.69-74
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• 2004

In scramjet engines with sidewall compression inlet, it is well known that a non-uniform flow appears since a separated region is generated near the flow centerline on the body side. The separated region is caused by shock-boundary layer interaction and likely to cause un-start phenomena since the flow in the separated region is subsonic and acts as a communication path between the isolator and the combustor. In the present study, the non-uniform flow characteristics in the scramjet inlet-isolator region are numerically studied in detail. Effect of flow suction from body sidewall surface on the non-uniform flow field numerically examined to clarify the flow mechanism to suppress the un-start transition.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.3
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• pp.397-404
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• 2011

The aerodynamic characteristics of a separated captive body in flow field around aircraft are studied to observe aerodynamic stability for safe separation from aircraft. Since the captive body separated from aircraft is initially exposed to unsteady flow pattern, the change of aerodynamic forces and moments should be measured to analyze how the flow pattern affects on the captive body at the vicinity of aircraft. Aerodynamic forces and moments of the separated captive body are measured at selected positions along predictable dropping trajectories. The measuring trajectories, generated by the free drop test of the dropping model in the wind tunnel, are consisted of 9 possible lines by free dropped trajectories. Experimental results show that the aerodynamic forces and moments are significantly varied with the distance between the captive body and aircraft. In conclusion, the change of aerodynamic characteristics within flow field around aircraft should be considered to simulate trajectories of the separated captive body from aircraft.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.9-18
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• 2010

There are two kinds of models in two-phase pressured drop; homogeneous flow model and separated flow model. Many previous researchers have developed correlations for two-phase pressure drop in a microchannel. Most correlations were modified Lockhart and Martinelli's correlation, which was based on the separated flow model. In this study, experiments for adiabatic liquid water and nitrogen gas flow in rectangular microchannels were conducted to investigate two-phase pressure drop in the rectangular microchannels. Two-phase frictional pressure drop in the rectangular microchannels is highly related with flow regime. Homogeneous model with six two-phase viscosity models: $Owen^{(21)}$'s, $MacAdams^{(22)}$'s, Cicchitti et ${al.}^{(23)}$'s, Dukler et ${al.}^{(24)}$'s, Beattie and ${Whalley}^{(25)}$'s, Lin et ${al.}^{(26)}$'s models and six separated flow models: Lockhart and $Martinelli^{(27)}$'s, ${Chisholm}^{(31)}$'s, Zhang et ${al.,}^{(15)}$'s, Lee and ${Lee}^{(5)}$'s, Moriyama and ${Inue}^{(4)}$'s, Qu and $Mudawar^{(8)}$'s models were assessed with our experimental data. The best two-phase viscosity model is Beattie and Whalley's model. The best separated flow model is Qu and Mudawar's correlation. Flow regime dependency in both homogeneous and separated flow models was observed. Therefore, new flow pattern based correlations for both homogeneous and separated flow models were individually proposed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.467-476
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• 2000

An unsteady numerical simulation was performed for locally-forced separated and reattaching flow over a backward-facing step. The local forcing was given to the separated and reattaching flow by means of a sinusoidally oscillating jet from a separation line. A version of the $k-{\varepsilon}-f_{\mu}$ model was employed, in which the near-wall behavior without reference to distance and the nonequilibrium effect in the recirculation region were incorporated. The Reynolds number based on the step height (H) was fixed at $Re_H=33000$, and the forcing frequency was varied in the range $0{\leq}St_H{\leq}2$. The predicted results were compared and validated with the experimental data of Chun and Sung. It was shown that the unsteady locally-forced separated and reattaching flows are predicted reasonably well with the $k-{\varepsilon}-f_{\mu}$ model. To characterize the large-scale vortex evolution due to the local forcing, numerical flow visualizations were carried out.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.87-95
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• 2001

A numerical study was made of heat transfer in locally-forced turbulent separated and reattaching flow over a backward-facing step. The local forcing was given to the flow by means of sinusoidally oscillating jet from a separation line. A Rhee and Sung version of the unsteady $\kappa$-$\varepsilon$-f(sub)u model and the diffusivity tensor heat transfer model were employed. The Reynolds number was fixed at Re(sub)H=33,000 and the forcing frequency was varied in the range 0$\leq$fH/U(sub)$\infty$$\leq$2. The condition of constant heat flux was imposed at the bottom wall. The predicted results were compared and validated with the experimental data of Chun and Sung and Vogel and Eaton. The enhancement of heat transfer in turbulent separated and reattaching flow by local forcing was evaluated and analyzed.

• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.458-466
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• 2007

This study is to evaluate control effects of separation wall by surveying water quality and sewer overflows during dry and wet periods in combined sewer and separated sewer systems. Ravine water from the combined Seokgyo outfall with the separation wall was separated about four times larger than sewage flow during dry periods. The water quality of the combined Seokgyo outfall with separation wall during dry periods is flow weighed average BOD 61 mg/L, the combined Cheonseokgyo outfall without the separation wall is average BOD 71 mg/L, and the separated Pyeongsong center outfall is average BOD 41 mg/L. The BOD concentration in separated outfall form about 57% of the combined outfall, and this means the separated outfall (i.e. storm sewer) is polluted by inflow of sewage. The overflow load of the separated outfall is ten times higher than the combined outfall and its overflow load per rainfall is three times than combined outfall during the wet periods. Therefore, the control plan of overflow load is required in storm sewer. The control effects of the overflow load increased 79% by setting the separation wall in the combined sewer, and showed 27% increase without the separation wall in separated sewer, but forecasted over 80% increase of effects if the separation wall was set.