• 한국가시화정보학회:학술대회논문집
• /
• 2001.12a
• /
• pp.108-122
• /
• 2001

In a continuing effect to study the mixmg enhancement by large-scale streamwise vortices in lobed mixing flows, an advanced PIV system named as dual-plane stereoscopic PIV system was used in the present study to conduct simultaneous vorticity (all three components) measurement of an air jet exhausted from a lobed nozzle. Unlike 'classical' 2-D PIV system or conventional 'single-plane' stereoscopic PIV system, the dual-plane stereoscopic PIV system used in the present study can obtain the flow velocity (all three components) fields at two spatially separated planes simultaneously. Therefore, it can provide the distributions of all the three components of vorticity vectors instantaneously and simultaneously. The evolution and interaction characteristics of the large-scale streamwise vortices and azimuthal Kelvin-Helmholtz vortices in the lobed jet mixing flow were revealed instantaneously and quantitatively from the measurement results of the dual-plane stereoscopic PIV system. The characteristics of the mixing process in the lobed jet mixing flow were analyzed based on the simultaneous measurement results of the steamwise vorticity and azimuthal Kelvin-Helmholtz vorticity distributions.

• The KSFM Journal of Fluid Machinery
• /
• v.7 no.6 s.27
• /
• pp.15-20
• /
• 2004

Numerical analysis of the partial admission turbine in the KARI turbopump has been performed. Flow field of the partial admission turbine is intrinsically unsteady and three dimensional. To avoid heavy computational efforts, the frozen rotor method is adopted in computation and compared with the mixing plane approach. The frozen rotor method can represent the variation of a flow field along the circumferential direction of rotor blades, which have the different relative positions to the nozzle with one another. It also illustrates the wake loss mechanism starting from the lip of a nozzle, which is not captured in the mixing plane method. The frozen rotor method has proven to be an efficient tool for the design of a partial admission turbine.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.9 no.1
• /
• pp.61-66
• /
• 2005

A theoretical analysis is developed for an annular-injection-type supersonic ejector having a second-throat downstream the ejector under the assumption that the Fabri choking is placed in mixing chamber. Non mixing theory is applied to formulate secondary flow pressure in the region between inlet of the mixing chamber and Fabri choking. To describe the shock standing at the inlet of the mixing chamber, two dimensional oblique shock relations are used and it is assumed that the shock affects only primary flow at Fabri choking plane. Physical constraint, which is that primary flow pressure and secondary flow pressure are same at Fabri choking plane, is added. In conclusion, it agrees well with experiments in case of small contracting angle of mixing chamber, under 4degrees.

• Journal of the Korean Society of Combustion
• /
• v.3 no.1
• /
• pp.59-69
• /
• 1998

The results of study on the active control of naturally occurring combustion oscillations with a single dominant frequency in an atmospheric dump combustor are presented. Control was achieved by an oscillatory infection of secondary fuel at the dump plane. A high speed solenoid valve with a maximum frequency of 250Hz was used as the actuator and a sound level meter, located at the combustor exit, measured the pressure fluctuations which served as the feedback signal for the control loop. Instability characteristics were mapped over a range of mean mixing section velocities from 6.7 m/s-9.3 m/s and with three mixing conditions. Different fuel/air mixing conditions were investigated by introducing varying percentages of primary fuel at two locations, one at the entrance to the mixing section and one 6 mixing tube diameters upstream of the dump plane. Control studies were conducted at a mean velocity of 9.3 m/s, with an air temperature of $415^{\circ}C$, and from flame blowout to the stoichiometric condition.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.3
• /
• pp.316-325
• /
• 1998

The objective of this study is to investigate the role of large-scale coherent structures in a spatially developing plane mixing layers. To achieve this, we have to look into the mutual interactions between three-dimensional large-scale coherent structures and the mean flow. Our attention will be focused on the energy exchange mechanism between the various modes, and the effects of the nonlinear evolution of the phases of the interacting modes. Linear stability of the three-dimensional viscous shear layer is formulated and solved as the basis for the solution of the nonlinear formulation based on the energy method. The importance of the initial conditions that may affect the evolution of the flow has been examined. It has been numerically calculated the nonlinear effects arising from the interactions among the three-dimensional large-scale coherent structures in a spatially developing plane mixing layers. The results of this study provide useful parametric information for the control of shear layer in practical applications in the mixing and transport augmentation.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.9 no.2
• /
• pp.97-104
• /
• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.11
• /
• pp.919-925
• /
• 2016

In this study, the Lamb wave mixing technique, which is basised on advanced research on the nonlinear bulk wave mixing technique, is applied for corrosion detection. To demonstrate the validity of the Lamb wave mixing technique, an experiment was performed with normal and corroded specimens. Comparison group in an experimentation are selected to mode and frequency with dominant in-plane displacement and out-of-plane displacement of Lamb waves. The results showed that the Lamb wave mixing technique can monitor corrosion defects, and it has a trend similar to that of the conventional Lamb wave technique. It was confirmed that the dominant displacement and mode matching the theory were generated. Flaw detectability is determined depending on displacement ratio instead of using the measurement method and mode selection.

• 제어로봇시스템학회:학술대회논문집
• /
• 1992.10b
• /
• pp.388-393
• /
• 1992

An infrared range finder using a self-mixing laser diode (SM-LD), which has been proposed and developed by the Authors, can measure not only a range of a moving target but its velocity simultaneously. In this paper, described is that the precise mode-hop pulse train can be obtained by employing a new signal processing circuit even when the backscattered light returning into the SM-LD is much more weaker. As a result, the distance to a tilted square sheet made from aluminium or white paper, which is placed 10 cm through 60 cm from the SM-LD, is measured with accuracy of a few percent even when the tilting angle is less than 75 degrees or 85 degrees, respectively. And in this paper, described is the range-image recognition of a plane object under the condition of standstill. The output laser beam is scanned by scanning two plane mirrors-equipped with each stepping motor. And we succeeded in the acquisition of the range-image of a plane object in a few tens of seconds. Furthermore, described is a feasibility study about the range-image recognition of a slowly moving plane object.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.1
• /
• pp.48-53
• /
• 2005

The purpose of this investigation is to explore the possibility of using artificial mechanical means for excitation of shear layers with application in swirling jet mixing enhancement. For this purpose, a mechanical excitation device was designed and fabricated. The major system components consist of two subsonic nozzles, one swirl generator, and the excitation device. The experiments were carried out at various helical excitation modes; i.e., m=+0, m=$\pm$1, m=$\pm$2, m=$\pm$3, and m=$\pm$4. Axial mean velocity measurements were made with plane and helical wave excitation using a hot-wire anemometer. The results are compared with the baseline (plane-wave excitation) at various helical modes. The acquired data is presented in 3-D mesh plots and 2-D contour plots. It was observed that new device was effective in excitation of the helical instability waves and resulting in mixing enhancement of the swirling jet.

• Journal of the Korean Vacuum Society
• /
• v.3 no.3
• /
• pp.316-321
• /
• 1994

Rate of mixing of Cu particles to polyimide substrate at interfaces under different thermal treatments was analyzed by Rutherford Backscattering spectroscopy using 2.0 MeV He+ ions. T he mixing rate was a function of annealing temperature and time and was constant at afioxed temperature. The amount of mixing increased linearly with time and the mixing rate increased with temperature. The activation energy for interface mixing between Cu and polyimide was 2.6 kcal/mol. The X-ray studies showed the Cu(111) plane peak changed with annealing time at fixed temperature. The mixing of Cu to polyimide was explained with segmental motion of PI chain and with interaction between functional group of the chain and metal electron donor. The comparisons were made bewteen the mixing induced by ion irradiation and by thermal treatment. The various factors affecting the interface mixing are discussed.