• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.381-385
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• 2004

본 인구에서는 레이놀즈응력모형을 이용하여 직사각형 개수로 흐름을 수치모의 하고 이차흐름의 생성 메커니즘을 제시하였다. 수치모의 결과 자유수면과 측벽의 접합부 근처에서 inner secondary flow가 발생하였다. 이는 최근 Grega 등(1995)과 Hsu 등(2000)에 의해 밝혀진 새로운 이차흐름이다. 또한 측벽에서의 전단력 분포를 계산한 결과 inner secondary flow에 의하여 수면 근처에서의 전단력 값이 증가하는 것으로 나타났다. 계산된 결과를 이용하여 와도 방정식에서 각 항의 크기를 비교하여 이차 흐름의 생성 메커니즘을 살펴보았다. 그 결과 벽 및 측벽 경계 부근에서는 난류의 비등방성에 의한 와도 생성항에 의해 이차 흐름이 생성되고, 경계와 멀리 떨어진 영역에서는 레이놀즈응력에 의한 와도 생성항이 이차흐름을 생성시키는데 중요한 역할을 하는 것으로 나타났다.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.58-66
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• 1999

The flow characteristics of supersonic ejectors is often subject to compressibility, unsteadiness and shock wave systems. The numerical works carried out thus far have been of one-dimensional analyses or some Computational Fluid Dynamics(CFD) which has been applied to only a very simplified configuration. For the design of effective ejector-pump systems the effects of secondary mass flow on the supersonic ejector flow should be fully understood. In the present work the supersonic ejector-pump flows with a secondary mass flow were simulated using CFD. A fully implicit finite volume scheme was applied to axisymmetric compressible Navier-Stokes equations. The standard two-equation turbulence model was employed to predict turbulent stresses. The results obtained showed that the flow characteristics of constant area mixing tube types were nearly independent of the secondary flow rate, but the flow fields of ejector system with the second-throat were strongly dependent on the secondary flow rate due to the effect of the back pressure near the primary nozzle exit.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3529-3533
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• 2007

The advantages of the SITVC(secondary injection thrust vector control) technique over mechanical thrust vector systems include a reduction in both the nozzle weight and complexity due to the elimination of the mechanical actuators that are used in conventional vectoring. Computational study is performed to understand the fluidic thrust vectoring control of an axisymmetric nozzle, in which secondary gas injection is made in the divergent section of the nozzle. The nozzle has a design mach number 3. The effect of injection hole number and shape of secondary jet on the mach number distribution of SITVC were investigated. The standard ${\kappa}$ - ${\epsilon}$ turbulence model solved the complex three-dimensional nozzle flows perturbed by the secondary gas jet. The numerical code was validated by experiment. The results showed that the mach number distribution of circular and square nozzle are similar each other. As number of second injection hole increasing, a effect of deflection was decreased.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.646-651
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• 2001

The present study is an experimental work of the sonic/supersonic air ejector-diffuser system. The pressure-time dependence in the secondary chamber of this ejector system is measured to investigate the steady operation of the ejector system. Six different primary nozzles of two sonic nozzles, two supersonic nozzles, petal nozzle, and lobed nozzle are employed to drive the ejector system at the conditions of different operating pressure ratios. Static pressures on the ejector-diffuser walls are to analyze the complicated flows occurring inside the system. The volume of the secondary chamber is changed to investigate the effect on the steady operation. the results obtained show that the volume of the secondary chamber does not affect the steady operation of the ejector-diffuser system but the time-dependent pressure in the secondary chamber is a strong function of the volume of the secondary chamber.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.4
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• pp.50-56
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• 2001

The present study is an experimental work of the soni $c^ersonic air ejector-diffuser system. The pressure-time dependence in the secondary chamber of this ejector system is measured to investigate the steady operation of the ejector system. Six different primary nozzles of two sonic nozzles, two supersonic nozzles, petal nozzle, and lobed nozzle are employed to drive the ejector system at the conditions of different operating pressure ratios. Static pressures on the ejector-diffuser walls are to analyze the complicated flows occurring inside the system. The volume of the secondary chamber is changed to investigate the effect on the steady operation. the results obtained show that the volume of the secondary chamber does not affect the steady operation of the ejector-diffuser system but the time-dependent pressure in the secondary chamber is a strong function of the volume of the secondary chamber.er.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.825-830
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• 2001

A numerical study on a quantitative analogy of the fully developed flow between in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of two turbulent flows, the dimensionless parameters $K_{TR} = Re^{1/4}/\sqrt{Ro}$ and the Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to $K_{TC} = Re^{1/4}/\sqrt{{\lambda}}$ and curvature ratio, ${\lambda}$, in a stationary curved duct flow so that they have the same dynamical meaning as $K_{LR} = Re/\sqrt{Ro}$ and $K_{LC} = Re/\sqrt{{\lambda}}$ of the fully developed laminar flows. For the large values of Ro or A, it is shown that the flow field satisfies the asymptotic invariance property: there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of $K_L$ and $K_T$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.842-849
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• 2002

The present study showed that a quantitative analogy of the fully developed laminar flows inorthogonally rotating rectangular ducts and stationary curved rectangular ducts of arbitrary aspect ratio could be established. In order to clarify the similarity of the two flows, the dimensionless parameters $K_{LR}$ =Re/√Ro and Rossby number Ro= $w_{m}$/$\Omega$d in a rotating strait duct were used as a set corresponding to Dean number $K_{LC}$ =Re/√λand curvature ratio λ=R/d in a stationary curved duct. Under the condition that the value of Rossby number and curvature ratio was large enough, the flow field satisfied the ‘asymptotic invariance property’: there were strong quantitative similarities between the two flows such as friction factors, flow patterns, and maximum axial velocity magnitudes for the same values of $K_{LR}$ and $K_{LC}$ .

• Journal of computational fluids engineering
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• v.6 no.1
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• pp.21-30
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• 2001

A numerical study on the similarity of the developing laminar flows between in a straight duct rotating about an axis perpendicular to that of the duct and in a stationary curved duct was carried out. In order to clarify the analogy of two flows, dimensionless parameters K/sub LR/ = Re/(equation omitted) and Rossby number, Ro, in a rotating straight duct were used as a set corresponding to Dean number K/sub LC/ = Re/(equation omitted), and curvature ratio, λ, in a stationary curved duct. For the large values of Ro and λ, it is shown that the flow field satisfies the 'asymptotic invariance property', that is, there are strong quantitative similarities between the two flows such as flow patterns, friction factors, and maximum axial velocity magnitudes for the same values of K/sub LR/ and K/sub LC/ if they are correlated with dimensionless axial distances Z/sub R/ = z/(equation omitted) for a rotating duct flow and Z/sub C/ = z/(equation omitted) for a stationary curved duct flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.185-194
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• 1984

The finite analytic method is extended to solve the steady two dimensional Navier-Stokes equation of stream functions and vorticity in polar coordinate system. The method is applied to calculate laminar flows in a sector cavity where the motion is induced by the rotation of the outer wall. Numerical solutions are obtained in the range of Reynolds number 0 to 5000 and aspect ratios 0.50, 1.20, 1.60 and 1.92. The finite analytic method is verfied to be accurate and fast convergent at high Reynolds numbers. It is promising as a numerical method of viscous flows and heat transfer. Flows in sector cavities show different flow structures and formation of secondary vortex with aspect ratios and Reynolds numbers in comparison with rectangular cavities.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.157-164
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• 2015

The present work performs three-dimensional flow calculations based on Reynolds Averaged Navier-Stokes (RANS) and Delayed Detached Eddy Simulation (DDES) to investigate the flow field of a transonic rotor (NASA Rotor 37) at near-stall condition. It is found that the DES approach is likely to predict well the complex flow characteristics such as secondary vortex or turbulent flow phenomenon than RANS approach, which is useful to describe the flow mechanism of a transonic compressor. Especially, the DES results show improvement of predicting the flow field in the wake region and the model captures reasonably well separated regions compared to the RANS model. Besides, it is discovered that the three-dimensional vortical flows after the vortex breakdown from the rotor tip region are widely distributed and its vortex structures are clearly present. Near the rotor leading edge, a part of the tip leakage flows in DES solution spill over into next passage of the blade owing to the separation vortex flow and the backflow is clearly seen around the trailing edge of rotor tip. Furthermore, the DES solution shows strong turbulent eddies especially in the rotor hub, rotor tip section and the downstream of rotor trailing edge compared to the RANS solution.