• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.51-58
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• 2002

The RPV(Reaction Progress Variable) combustion model has been applied to numerically investigate the effects of Damkohler number on the superequilibrium concentration and flame structure in the nonpremixed turbulent flames. Computations are performed for the two turbulent jet flames of CO/H$_2$/N$_2$(40/30/30 volume percent) having the same jet Reynolds number of 16,700 but different nozzle diameters(4.58mm and 7.72mm). The detailed discussions have been made for the interaction between fluid dynamics and chemistry in the flame field.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.10a
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• pp.5-9
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• 1995

In the dry-jet-wet-spinning process of a hollow fiber membrane, the polymer solution is pumped into a coaxial tube, jet spinneret. The threadline emerging from the spinneret is stabilized by an internal coagulating medium(liquid or gas) as it emerges from the jet orifice. The nascent hollow thread is further stabilized in a quench bath as shown in Fig. 1. In this scheme, three mechanism of formatiota(temperature gradient, solvent evaporation, and solvent-nonsotvent exchange) can be combined. The changes which promote stabilization often play a dominant role in determining the ultimate fiber wall structure as well. Hence, in pratice, hollow fiber stabilization and development of membrane structure are commonly inseparable. However, fiber dimension(the inside diameter and wall thickness of the hollow fiber) is mainly a rheological problem and is determined by dope pumping rate, spinneret diatance from the coagulation bath, inner coagulant flow rate, and fiber draw-rate. Besides rheological phenomena play a prominent part in the final properties of the hollow fiber.

• Journal of ILASS-Korea
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• v.4 no.4
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• pp.38-45
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• 1999

The near field structure of round turbulent jets with initially asymmetric velocity distribution is investigated experimentally. Experiments were carried out using a constant temperature hot-wire anemometry system to measure streamwise velocity in the jets. The measurements were undertaken across the jet at various streamwise stations in a range starting from the jet exit plane and up to a downstream location of twelve diameters. The experimental results include the distribution of mean and instantaneous velocities, vorticity field, turbulence intensity, and the Reynolds shear stress. The asymmetry of the jet exit plane was obtained by using circular cross-section pipes with a bend at the upstream of the exit. Three pipes were used for this study: A straight pipe, 90 and 160 degree-bended pipes. Therefore, at the upstream of the pipe exit, the secondary flow through the bend and the mean streamwise velocity distribution could be controlled by changing the curvature of pipes.

• Journal of computational fluids engineering
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• v.6 no.3
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• pp.32-40
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• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum mean pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.12
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• pp.1173-1183
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• 2009

In order to reduce the download around the Smart UAV(SUAV) at hovering, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including the leading and trailing edge separation, and the large region of separated flow beneath the wing. In order to control the leading edge and trailing edge separation, synthetic jet is located at 0.01c, $0.3c_{flap}$, $0.95c_{flap}$. As non-dimensional frequency, the flow pattern is altered and the rate of drag reduction is changed. The results show that synthetic jets shorten the vortex period and decrease the vortex size by changing local flow structure. By using leading edge jet and trailing edge jet, download is efficiently reduced compared to no control case at hovering mode.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.986-993
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• 2018

Lateral thrust jet has better maneuverability performance than the control surface like the conventional fin for attitude control or orbital transition of guided weapons. However, in the supersonic region, a jet interaction flow occurs due to the lateral thrust jet during flight, and a complicated flow structure is exhibited by the interaction of the shock wave, boundary layer flow, and the vortex flow. Especially, hit-to-kill interceptors require precise control and maneuvering, so it is necessary to analyze the effect of jet interaction flow. Conventional jet interaction analyses were performed under low altitude conditions, but there are not many cases in the case of medium altitude condition, which has different flow characteristics. In this study, jet interaction flow analysis is performed on the lateral jet controlled interceptor operating at medium altitude. Based on the results, the structural characteristics of the flow field and the changes of aerodynamic coefficient are analyzed.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.83-93
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• 2017

A numerical analysis is made of the fluid flow and heat transfer characteristics in the corrugated structure that traps the spent air in the corrugations between impinging jets to reduce crossflow effects on downstream jets in the array. All computations are performed by considering three-dimensional, steady state, and incompressible flow by using the ANSYS-CFX 15.0 code. Averaged jet Reynolds number is 10,000. The oblique angles of impingement jets on the spanwise section are $70^{\circ}$, $80^{\circ}$, $90^{\circ}$, and the oblique angles of impingement jets on the streamwise section are $70^{\circ}$, $90^{\circ}$, $110^{\circ}$. The investigation focuses on the oblique angle influence of impinging jet array on the fluid flow and heat transfer characteristics of a corrugated structure.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.51-56
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• 2005

Acoustic excitations were imposed to coaxial air jet of non-premixed jet flame with hydrogen gaseous injected axially in the center of the flow. The frequencies of excitation were three dominant resonant frequencies at 1L, 2L, 3L. modes including specially 514 Hz (2L-mode) which was estimated theoretically as longitudinal mode of combustor characteristics. The mixing enhancement by acoustic forcing has been investigated quantitatively using PLIF and PIV. The effect of acoustic excitation on combustion process was significant to enhance mixing rate that coincides with specific resonant frequencies. And the behavior of vortex-interaction on flame structure was a good evidence to investigate the phenomenon of shear/mixing layer of fuel-air jet structure. The results obtained in this study concludes that generated streamwise vortex by acoustic excitation has a potential to enhance the mixing rate and abating NOx emissions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.96-101
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• 1986

The average heat transfer coefficient of 2-D impinging jet has been augmented as much as 60% on the wall with large-scale wavy roughness. The mechanism of this heat transfer augmentation is studied with emphasis on two primary flow structures in the impinging flow region by using either the surface floating method or the smoke-wire technique. They are the stream-wise vortex-like structure, which is characteristic to the impining jet, and the spanwise vortiecs associated with the flow separation around the roughness. The combined effect of these structures can effectively augment the heat transfer particularly in the downstream region where the teat transfer usually deteriorates consicerably.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.84-91
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• 2005

An experimental investigation has been carried out to examine heat-transfer characteristics of an axisymmetric, under-expanded, sonic jet impinging on a flat plate and the local measurement of surface pressures and heat transfer coefficients on a plate have been achieved together with a visualization test of shock structure in a jet. Heat transfer coefficients on a plate have been found to be changed significantly depending on the under-expansion ratio as much as the nozzle-to-plate distance. These phenomena could be explained by the wall pressure measurement and the shock visualization.