• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.187-195
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• 2012

This paper deals with numerical computations of cryogenic flows around turbopump inducer. Firstly, we introduce numerical methods to compute compressible/incompressible cryogenic two-phase flow. As a validation problem, computation results of 2 dimensional/axi-symmetric cryogenic flow will be presented. In this process, various cavitation model will be compared. Finally, numerical simulation of 3 dimensional turbopump inducer will be presented.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2294-2303
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• 1993

This paper investigated the characteristics of the turbulent incompressible flow past the orifice ring in an axi-symmetric pipe. The flow field was the turbulent pulsatile flow for Reynolds number of $2{\times}10^{5}$ which was defined based on the maximum velocity and the pipe diameter at the inlet, with oscillating frequence $(f_{os})=1/4{\pi}$ which was considered as quasi-steady state frequence. In the present investigation, finite analytic method was used to solve the governing equations in Navier Stokes and turbulent transport formulations. Particularly at high Reynolds number and low oscillation frequency, the effects of orifice ring on the flow were numerically investigated. The separation zone behind the orifice ring during the acceleration phase was found to be decreased. However, during the deceleration phase, the separation behind the orifice ring for pulsatile flow continuously grow to a size even larger than that in steady flow. The pressure drop in steady flow was found to be constant and always positive while for pulsatile flow the pressure drop change with time. And large turbulent kinetic energy, dissipation rate were found to be located in the region where the flow passes through the orifics ring. The maximum turbulent kinetic energy, generally occurs along the shear layer where the velocity gradient is large.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.287-294
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• 2005

Flow rate measurement uncertainties of the ultrasonic flow meter are generally influenced by many different factors, such as Reynolds number, flow distortion, turbulence intensity, wall surface roughness, velocity integration method along the acoustic paths, and transducer installation method, etc. Of these influencing factors, one of the most important uncertainties comes from the velocity integration method. In the present study, a optimization weighting factor method for 5-chord, which is given by a function of the chord locations of acoustic paths, is employed to obtain the mean velocity in the flow through a pipe. The power law profile is assumed to model the axi-symmetric pipe flow and its results are compared with the present weighting factor concept. For an asymmetric pipe flow, the Salami flow model is applied to obtain the velocity profiles. These theoretical methods are also compared with the previous Gaussian, Chebyshev, and Tailor methods. The results obtained show that for the fully developed turbulent pipe flows with surface roughness effects, the present weighting factor method is much less sensitive than Chebyshev and Tailor methods, leading to a better reliability in flow rate measurement using the ultrasonic flow meters.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.57-66
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• 2011

Radial-vaned air separators show a strong stall suppression effect in an axial flow fans. From a survey of existing literature on the effects and the author's data, a possible mechanism for the significant effects has been proposed here. The stall suppression is suggested to have been achieved by a combination of the following several effects; (1) suction of blade and casing boundary layers and elimination of embryos of stall, (2) separation and straightening of reversed swirling flow from the main flow, (3) induction of the fan main flow toward the casing wall and enhancement of the outward inclination of meridional streamlines across the rotor blade row, thus keeping the Euler head increase in the decrease in fan flow rate, and (4) reinforcement of axi-symmetric structure of the main flow. These phenomena have been induced and enhanced by a stable vortex-ring encasing the blade tips and the air separator. These integrated effects appear to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices. Thus the author would like to name the device "tip-vortex-ring assisted stall suppression device".

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.46-52
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present study was 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 33 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.26-29
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• 2004

In this paper, we report the numerical and experimental solutions of the dynamic characteristics of a vortex ring in a circular cylinder generated by impinging a fluid blob from a hole on the bottom wall of the cylinder. We managed to visualize successfully the flow pattern shown on the vertical and horizontal planes by using a specially designed optical apparatus. Results of three-dimensional computation for the flow are shown to be in a satisfactory agreement with the experimental ones. We also report the experimental results which show a breaking of the axi-symmetric pattern after the vortex touches the free surface.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.166-170
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present studywas 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 34 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.3
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• pp.8-14
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• 2003

A cooling performance analysis has been made in the 8-channel calorimeter based on sub-scale KSR-III engine. Three-dimensional heat transfer analysis in cooling channels has been performed using the heat flux distribution through the chamber wall predicted from axi-symmetric compressible flow inside the combustion chamber. The heat flux distribution is verified against the published literature. Presented for the development and operation of the calorimeter are the coolant pressure drop, coolant temperature rise and the maximum chamber wall temperature. Required coolant flow rate is determined for given chamber pressure. Cooling performance is also predicted for temperature dependant coolant properties.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.9 s.240
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• pp.1042-1048
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• 2005

Numerical investigation has been made on the stent design to minimize the neointimal hyperplasia. Computational fluid dynamics is applied to investigate the flow distributions in the immediate vicinity of the given idealized stent implanted in the blood vessel. Parametric study on the variations of the number of stouts, stent diameters, stent spacings and Reynolds numbers has been conducted using axi-symmetric Navier-Stokes equations. An initial difficulty in the study is to determine the optimal stent design to understand the flow physics of the flow disturbance induced by stent. The size of recirculation zone around stent is depend on the stent diameter, number of stent wire and Reynolds number but is insensitive to the stent wire spacing. It is also found that when the flow is in acceleration, the flow sees a more favorable pressure gradient, and the separation zones are smaller than the steady flow case. When the flow is in deceleration and the flow sees a more adverse pressure gradient so that the separation zones are larger.

• Journal of computational fluids engineering
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• v.4 no.2
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• pp.57-66
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• 1999

Numerical Analysis has been done for the supersonic off-design jet flow due to the pressure difference between the jet and the ambient fluid. The difference of pressure generates an oblique shock or an expansion wave at the nozzle exit. The waves reflect repeatedly on the center axis and the sonic surface in the shear layer. The pressure difference is resolved across these reflected waves. In this paper, the axi-symmetric Navier-Stokes equation has been used with the κ-ε turbulence model. The second order TVD scheme with flux limiters, based on the flux vector split with the smooth eigenvalue split, has been used to capture internal shocks and other discontinuities. Numerical calculations have been done to analyze the off-design jet flow due to the pressure difference. The variation of pressure along the flow axis is compared with an experimental result and other numerical result. The characteristics of the interaction between the shock cell and the turbulence mixing layer have been analyzed.