• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.458-466
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• 2007

This study is to evaluate control effects of separation wall by surveying water quality and sewer overflows during dry and wet periods in combined sewer and separated sewer systems. Ravine water from the combined Seokgyo outfall with the separation wall was separated about four times larger than sewage flow during dry periods. The water quality of the combined Seokgyo outfall with separation wall during dry periods is flow weighed average BOD 61 mg/L, the combined Cheonseokgyo outfall without the separation wall is average BOD 71 mg/L, and the separated Pyeongsong center outfall is average BOD 41 mg/L. The BOD concentration in separated outfall form about 57% of the combined outfall, and this means the separated outfall (i.e. storm sewer) is polluted by inflow of sewage. The overflow load of the separated outfall is ten times higher than the combined outfall and its overflow load per rainfall is three times than combined outfall during the wet periods. Therefore, the control plan of overflow load is required in storm sewer. The control effects of the overflow load increased 79% by setting the separation wall in the combined sewer, and showed 27% increase without the separation wall in separated sewer, but forecasted over 80% increase of effects if the separation wall was set.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.125-129
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• 2005

Flow control has been performed using synthetic jet on NACA23012. In order to improve aerodynamic performance, synthetic jet is located near separation paint on airfoil with leading edge droop and plain flap. The flow control using synthetic jet shows that stall characteristics and control surface performance can be improved through resizing separation vortices. Stall is delayed and stall characteristics are improved when synthetic jet is applied from separation region of leading edge droop. Control surface effectiveness is increased and lift is increased when synthetic jet applied at the flap leading edge region. The results show that aerodynamic characteristics can be improved through leading edge droop with synthetic jet at near separation and plain flap with synthetic jet at the flap leading edge. The combination of synthetic jet and simple high lift device is as good as fowler flap system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.928-933
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• 2007

In this research, we investigated active vibration control based on wave-viewpoint using the longitudinal wave separation method. The control strategy is the one of active vibration control technique for generating vibration reduced zone and uses wave information including the directivity as the cost function. In order to get the wave information from the measured values, we proposed and examined the time-domain longitudinal wave separation method proper to real time application like active vibration control. Using the proposed method, we examine the performance and feasibility of active vibration control based wave view-point through the simulation. The related experimental verification and application is going to be expected in a near future.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.43-50
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• 2009

In order to reduce the download around Smart UAV(SUAV) at hovering and transition mode, flow control using synthetic jet has been performed. Many of the complex tilt rotor flow features are captured including wing leading and trailing edge separation, and the large region of separated flow beneath the wing. First, in order to control the trailing edge separation, synthetic jet is located at 30, 95% of flap chord length. The flow control using synthetic jet on flap shows that stall characteristics depending on several mode can be improved through separation vortices resizing. Also, a flap jet and a 0.01c jet which control the separation efficiently are applied at the same time at each test case because controlling the leading edge separation is essential for download reduction. As a result, time averaged download is reduced about 18% comparing with no control case at hovering mode and 48% at transition mode. These research results show that if flow control using leading edge jet and trailing edge jet is used effectively to the SUAV in overall flight mode, flight performance and stability can be improved.

• Korean Membrane Journal
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• v.7 no.1
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• pp.42-50
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• 2005

Among ceramic membranes developed to date, amorphous silica membranes are attractive for gas separation at elevated temperatures. Most of the silica membranes can be formed on a porous support by sol-gel or chemical vapor deposition (CVD) process. To improve gas permselectivity of the membrane, well-controlled pores having desired size and chemical affinity between permeates and membrane become important factors in the preparation of membranes. In this article, we review the literature and introduce our technologies on the microstructure to be solved and pore size control of silica membranes using sol-gel and CVD methods.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.60-66
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• 2007

Separation control has been performed using synthetic jets on airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.1-8
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• 2005

This paper explored the effects of separation control through the use of pulsating jet blowing on a two dimensional elliptical airfoil. To develop an active control technique of flow separation, a flow control actuator utilizing continuous/pulsed jet of pressurized air was designed and installed in a wind tunnel testing model of elliptic wing. PIV measurement and flow visualization of the wing near field were conducted to access the feasibility and effectiveness of the pulsed jet blowing on controlling the stall of the elliptical wing in subsonic flow. PIV experimental results show that separation control can provide significant reduction in turbulent flow wake and separation bubbles by jet blowing. The pulsating jet blowing is more effective on the separation control than continuous one. Increased jet frequency suppressed the turbulent separated flow wake effectively at even higher AOAs.

• International Journal of Fluid Machinery and Systems
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• v.2 no.3
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• pp.215-222
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• 2009

Jets issuing through small holes in a wall into a freestream has proven effective in the control of flow separation. This technique is known as the vortex generator jet (VGJs) method. If a precursor signal of separation is found, the separation control system using VGJs can be operated just before the onset of separation and the flow field with no separation is always attained. In this study, we measured the flow field and the wall static pressure in a two-dimensional diffuser to find a precursor signal of flow separation. The streamwise velocity measurements were carried out in the separated shear layer and spectral analysis was applied to the velocity fluctuations at some angles with respect to the diffuser. The pattern of peaks in the spectral analysis changes as the divergence angle increases over the angle of which the whole separation occurs. This change in the spectral pattern is related to the enhancement of the growth of shear layer vortices and appears just before the onset of separation. Therefore, the growth of shear layer vortices can be regarded as a precursor signal to flow separation.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.3
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• pp.296-314
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• 2016

This paper presents experimental and computational investigations of synthetic jets with a circular exit for improving flow control performance. First, the flow feature and vortex structure of a multiple serial circular exit were numerically analyzed from the view point of flow control effect under a cross flow condition. In order to improve separation control performance, experimental and numerical studies were conducted according to several key parameters, such as hole diameter, hole gap, the number of hole, jet array, and phase difference. Experiments were carried out in a quiescent condition and a forced separated flow condition using piezoelectrically driven synthetic jets. Jet characteristics were compared by measuring velocity profiles and pressure distributions. The interaction of synthetic jets with a freestream was examined by analyzing vortical structure characteristics. For separation control performance, separated flow over an airfoil at high angles of attack was employed and the flow control performance of the proposed synthetic jet was verified by measuring aerodynamic coefficient. The circular exit with a suitable hole parameter provides stable and persistent jet vortices that do beneficially affect separation control. This demonstrates the flow control performance of circular exit array could be remarkably improved by applying a set of suitable hole parameters.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.7
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• pp.902-906
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• 2004

A separation principle of the Takagj-Sugeno (T-S) fuzzy-model-based observer-control is investigated. When the premise variables are able to be measured or directly computed from the outputs of the T-S fuzzy system and the fuzzy inference rules for the plant, control, and observer share the premise parts, the T-S fuzzy-model-based observer and the T-S fuzzy-model-based control can be separately designed such that the global stabilizability is guaranteed by the fuzzy observer-based output-feedback control. In this case, the global separation principle is well established. On the other hand, when the premise variables are unmeasurable or cannot be computed from the outputs, they should also be estimated. We examine the separation principle of this case. If the decay rates of the T-S fuzzy-model-based control and observer are sufficiently fast, the global separation is assured. Otherwise we show that the separation principle holds locally.