• 한국가시화정보학회지
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• 제10권2호
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• pp.20-24
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• 2012

Increasing the active catalyst surface area is important in improving a converter's efficiency. In addition, uniform flow is advantageous in that it produces more efficient catalytic conversion. This results in the ability to use a smaller catalytic converter with uniform flow as opposed to a larger converter requirement for non-uniform flow. Therefore, it is important to characterize the internal flow of the catalytic converter. To characterize the system's flow patterns, velocity measurements were taken at the mid and exit planes of a ceramic honeycomb catalytic converter at flow rates of 37.8 l/s and 94.4 l/s. Measurements were conducted using LDV. The profiles were measured along both the major and minor axis of the planes. Primary flow direction velocities measured along the minor axis, at both flow rates, varied greatly at the mid plane and somewhat at the exit plane. The areas of greatest air flow were seen near the edges of the walls and on the side of the converter opposite the flow's entrance region. It also appears that the high velocities opposite the intake are due to the design of the entrance region. The entrance region is possibly too small to properly redirect the vertically entering fluid into an evenly distributed flow in the primary flow direction.

• 한국농공학회지
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• 제34권E호
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• pp.45-59
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• 1992

At downstream part of the hydraulic structures such as spiliway or drainage gate, jet flow can occur by gate opening. If stream bed is not hard or bed protection is not sufficient, scour hole will be formed due to high shear stress of the jet flow. We call this primary scour. Once the scour hole is formed, a vortex occurs in it and this vortex causes additional scour. We call this secondary scour. The primary scour proceeds to downstream together with flow direction but the secondary one proceeds to upstream direction opposite to it. If the secondary one continues and reaches to the hydraulic structure, it can undermine the bottom of hydraulic structure and this will lead to failure of structure itself. Thus, it is necessary to know the physical features of the vortex structure in a scour hole, which is the main mechanism of the secondary scour. This study deals with the characteristics of the vortex structure and its shear stress which causes the secondary scour.

• 대한기계학회논문집B
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• 제20권9호
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• pp.2965-2972
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• 1996

Transitional flow in an obstructed channel is investigated using numerical simulation. Two-dimensional thin obstacles are mounted symmetrically in the vertical direction and periodically in the streamwise direction. Flow separation occurs at the tip of the sharp obstacles. Depending on the Reynolds number, the flow undergoes Hopf bifurcation as the primary instability leading to a two-dimensional unsteady periodic solution. At higher Reynolds numbers, the unsteady solution exhibits a symmetry-breaking bifurcation which results in an unsteady asymmetric solution. The results are compared with experiments currently available, and show a good agreement.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2011년도 한국우주과학회보 제20권1호
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• pp.29.1-29.1
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• 2011

The magnetic dipolarizations at the tail are often, if not always, associated with plasma flows of some magnitude. The associated flow direction is known to be earthward most often but not necessarily always. It is the primary goal of this paper to clarify the association between dipolarizations and the associated flow characteristics in general, but with a primary emphasis on tailward flow cases. Based on a number of dipolarizations that we identify at the near-Earth tail using the THEMIS tail observations we first confirm that dipolarizations can in general initiate in association with both earthward and tailward flows. Also, the main direction of the plasma flow, whether being earthward or tailward, is not critical in determining the intensity of the dipolarizations. We actually identify some events of tailward flow-associated dipolarizations that are as much intense as the earthward flow-associated events. The occurrence rate of the tailward flow-associated dipolarizations is mainly concentrated in the radial region of < 10 RE and in the local time region of 22-01 hr. However, its relative occurrence rate is rather low, ~19 % in the radial region and ~15.3 % in the local time region, as compared to that for the events associated with all other types of flows. Furthermore, the flow direction often changes no matter whether it is initially earthward or tailward near the onset time. As a consequence, the net transport of the magnetic flux during the main duration of the dipolarization process is earthward for nearly all of the dipolarizations that initiate with dominantly tailward flows near the onset, as is the case for those that initiate with dominantly earthward flows.

• 설비공학논문집
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• 제15권10호
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• pp.809-820
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• 2003

The present study investigates effects of flow velocity on the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewall are determined by using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The aspect ratio and corrugation angle of the wavy duct is fixed at 7.3 and 145$^{\circ}$ respectively, and the Reynolds numbers, based on the duct hydraulic diameter, vary from 100 to 5,000. The results show that there exist complex secondary flows and transfer processes resulting in non-uniform distributions of the heat/mass transfer coefficients on the duct side walls. At low Re (Re<1000), relatively high heat/mass transfer regions like cell shape appear on both pressure and suction side wall due to the secondary vortex flows called Taylor-Gortler vortices perpendicular to the main flow direction. However, at high Re (Re>1000), these secondary flow cells disappear and boundary layer type flow characteristics are observed on pressure side wall and high heat/mass transfer region by the flow reattachment appears on the suction side wall. The average heat/mass transfer coefficients are higher than those of the smooth circular duct due to the secondary flows inside wavy duct. And also friction factors are about two times greater than those of the smooth circular duct.

• 한국전산유체공학회지
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• 제18권2호
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• pp.99-108
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• 2013

The standard drag force and virtual mass force, which exert to the primary flow direction, are generally considered in two-phase analysis computational codes. In this paper, the lift force, wall lubrication force, and turbulent dispersion force including turbulence models, which are essential for a computational multi-fluid dynamics model and play an important role in motion perpendicular to the primary flow direction, were introduced and verified with conceptual problems.

• 대한기계학회논문집B
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• 제28권7호
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• pp.789-799
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• 2004

An experimental study is conducted to investigate the effects of duct corrugation angle on heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger application. Local heat/mass transfer coefficients on the wavy duct sidewalls are determined by using a naphthalene sublimation technique. The corrugation angles(${\alpha}$) of the wavy ducts are 145$^{\circ}$, 130$^{\circ}$, 115$^{\circ}$ and 100$^{\circ}$. And the Reynolds numbers based on the duct hydraulic diameter vary from 300 to 3,000. The results show that at the low Re(Re $\leq$1000), the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, high heat/mass transfer regions are formed on both pressure-side and suction-side walls. At the high Re(Re $\geq$ 1000), these secondary flows are vanished with helping flow transition to turbulent flow and the regions which show high heat/mass coefficients by flow reattachment are formed on suction side. As corrugation angle decreases, the local peak Sh induced by Taylor-Gortler vortices increase at Re $\leq$1000. At high Re(Re $\geq$ 1000), by the existence of different kind of secondary flows called Dean vortices, non-uniform Sh distribution appears along spanwise direction at the narrow corrugation angle (${\alpha}$=100$^{\circ}$). Average Sh also increase by the enhanced effect of secondary vortices and flow reattachment. More pumping power (pressure loss) is required with the smaller corrugation angle due to the enhancement of flow instability.

• 대한토목학회논문집
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• 제29권1B호
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• pp.35-45
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• 2009

본 연구에서는 사행수로에서 유속구조가 추적물질의 혼합에 미치는 영향을 분석하기 위하여 2개의 만곡부를 갖는 S자형 실험수로를 제작하여 순간 주입된 추적자물질에 대한 분산실험을 수행하였다. 실험자료를 분석한 결과, 주 흐름은 사행수로의 최단경로를 따라 이동하며 만곡부에서 불균일한 분포를 갖는 것으로 밝혀졌다. 이차류의 경우, 만곡부에서 강력한 셀이 발달하나 직선부에서는 소멸하다가 다시 다음 만곡부에 반대 방향의 셀로 재생성됨이 확인되었다. 오염운의 거동은 주흐름의 불균일한 분포와 이차류셀에 의해 매우 큰 영향을 받는 것으로 나타났다. 주흐름의 불균일한 분포는 오염운을 종방향으로 분리시키고, 이차류 셀은 만곡부 외측의 처진 오염운을 횡방향으로 더욱 분리시키는 역할을 하게 되어, 결과적으로 만곡부의 복잡한 유속구조가 오염운을 종 횡방향으로 모두 분리시키고 나아가서 많이 퍼지게 하는 작용을 하는 것으로 밝혀졌다. 2차원 추적법의 적용을 통해서 각 케이스별 종 횡분산계수 실측치를 산정한 결과, 사행수로 전체구간에 대한 무차원 횡분산계수는 0.012~0.875의 범위를 갖는 것으로 밝혀졌다. 횡분산계수는 하폭 대 수심비에 대체적으로 비례하는 것으로 나타났다. 횡분산계수 이론식에 의한 추정치와 비교한 결과, 이론치가 실측치와 비교하여 다소 과대 산정하는 경향을 보여주고 있음을 알 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.858-863
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• 2001

In this paper, the test and result of flow and combustion for 21AFR lean fuel models are described. The necessity to develop the low emission combustor has been issued from the concern on the increase of green house and the destruction of ozone layer. To evaluate the flow and combustion performance of new designed 21AFR lean modules, the hydraulic tests in stereo lithographic airflows models, the low pressure combustion tests in three injectors model for weak extinction and ignition and the high pressure combustion tests in single sector for NOx, SAE and efficiency are performed. The low pressure tests reveal that the governing parameters in weak extinction and ignition at atmospheric condition are prefilmer length, swirl flow rotation direction, secondary swirl angle and flow split. As a results of combustion test at high pressure, the efficiency and smoke level are satisfied with performance targets, but EINOx of 17.8 is higher than target value of 13.1. The high pressure tests show that the main parameters influenced on NOx are primary swirl angle, swirl flow rotation direction, heatshield exit angle and liner mixing hole location.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.467-472
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• 2000

Most of the past experimental or analytical studies were performed for the curved bend with a square cross-section. Velocity profiles and Reynolds stresses of the turbulence flow in the 270 degree bend with circular cross-section were measured by a hot-wire anemometer. The mean velocity of primary flowing direction effected by the downstream of bend in the entry region of the bend. The flow in the inner part of the bend slowed the distribution velocity relatively large and unsymmetric phenomenon. In the strong secondary flow occurred when the flow passed in the region of 45 degree to 90 degree. The secondary flow appeared very large value in the neighbor region of inner wall.