• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.61-61
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• 2002

스크램 제트 엔진의 설계에서 초음속으로 유입된 공기의 짧은 잔류시간으로 인한 연료-공기의 혼합은 가장 중요하며 해결하기 힘든 문제이다. 전헝적인 비행 조건에서 흡입 공기가 극초음속 비행기 엔진 내에서 잔류하는 시간의 단위는 1 ms 정도이어서 짧은 시간 동안 연료와 공기는 효율적으로 혼합되어야 하며, 최대의 추진력을 얻기 위하여 과도한 공력저항없이 연소 가능한 연료-공기 혼합기를 생성시킬 수 있는 효율적인 연료-공기의 혼합 방법이 요구된다. 현재까지 가장 많이 연구되어 온 혼합 방법은 엔진 입구로 들어오는 공기 유동에 수직 방향으로 연료를 분사하는 것으로 이 방법은 연료 유동 방향과 공기 유동 방향이 수직이기 때문에 추력 손실이 생기는 단점을 갖고 있지만, 초음속으로 유입되는 공기에 수직으로 연료를 분사하게되면 분사 위치 앞에 궁형 충격파가 생겨서 감속되어 유동이 회전하는 재순환영역이 생기고 연료의 혼합이 잘 이루어지는 장점이 있다.

• The KSFM Journal of Fluid Machinery
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• v.6 no.2 s.19
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• pp.15-22
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• 2003

Comprehensive study on a centrifugal blower for air-purifier involving a few physical filters for percolation process has been accomplished for an optimal design of the air handling system. The filtering media causes a flow resistance for induced flows by a rotating impeller. The present methodology is to adopt PIV system for velocity measurements and wind tunnel connected with an anechoic chamber for total performance test of the blower. Trial prototypes for the blades of a rotor and casing are presented for satisfaction of both flow rate and noise level set by design objectives. Tapered blades with a special casing for a fan show good performance data. The results of velocity fields also explain the reason of improvements of the blower performance.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.65-68
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• 2004

The design procedure for centrifugal blower with high inlet resistance is not presented yet. Overall fluid dynamic performance is estimated for comparison between the case of atmospheric inlet condition and the present model. Detail information between blades is prepared by using a commercial program, SCRYU-Tetra. A centrifugal blower with large inlet pressure is adopted in an air purifier having filtering devices. As the inlet residence increases the flow rate of the system is decreased. In parallel, outlet area of the system affects the performance of the system in the sense of flow balance. Consequently, the flow balance between the inlet and outlet becomes an important parameter for the design of the scroll casing for the centrifugal blower with high inlet pressure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1011-1014
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• 2006

Turbo blower generates high peaks when it operates at high pressure region. The fan of the air-cleaner system, operates especially high pressure region due to several filters, generates high noise level. In this case, the tonal sound of BPF makes people annoyance. The blower of air-cleaner has several high resistance filters in its inlet area and rotates above 900rpm Moreover, for the compact design, the size of the blower should be reduced 10%. The reduced diameter of blower makes low flow rate and high noise level. In order to reduce the noise, new blade shape was suggested and optimized

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.70-77
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• 2004

Comprehensive investigation on the outlet's geometric shapes of a centrifugal blower with higher inlet resistance than an atmospheric pressure is carried out for improvements of its performance. Most unwanted behaviors of such blower are pulsating flows because of unbalance between inflows and outflows in a scroll casing. In order to reduce this undesirable phenomenon a triump is made for both the shape of outlet duct and an accessory structure inserted in the outlet port of the blower. The modification on the shape is concerned with the contraction of cross sectional area and the attached structure is for an intentional obstruction to cause a flow resistance. The details of the modification are examined for different cases and results. The methodologies for the work are performance evaluations including noise level and velocity measurements with PIV Consequently, the performance of improved system is close to that of the system operating with atmospheric pressure at the inlet.

• Journal of Biosystems Engineering
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• v.7 no.2
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• pp.57-71
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• 1983

마찰식 정미기의 성능에 영향을 미치는 기계설계 및 작동상의 인자로는 스크린의 형태, 롤러의 형태, 롤러회전속도, 출구 저항 등 여러가지가 있다. 이러한 요인들에 대한 연구가 본 논문의 저자에 의해서 시리즈로 연구되어 왔으며, 본 연구는 그의 일환으로 스크린의 단면형상(6각, 8각, 12각 그리고 원통형), 스크린에 뚫려있는 슬랏의 기울기($15^{\circ}$, $30^{\circ}$, $45^{\circ}$ 그리고 $-45^{\circ}$), 그리고 출구 저항이 정백미의 질과 양, 정백효율 그리고 정백실내의 정백압력 등에 미치는 영향을 규명하기 위해 수행되었다. 이 실험에 사용된 공시 정미기는 임도정 공장에서 널리 사용되고 있는 흡입마찰식이었며, 사용된 시료는 밀양 23호인 통일계품종이었다. 각 처리마다 동력 소모량과 정백실내의 정백압력을 측정하기 위해서 "KYOWA" 스트레인 게이지 시스템(strain gauge system), 토오크 변환기, 압력변환기 등이 사용되었다. 본 실험 결과를 요약하면 다음과 같다. 1) 정백과정중에 정백실내의 정백압력은 입구에서 가장 높았고 출구쪽으로 갈수록 점차 감소하였다. 평균 정백압력도 순환 횟수에 따라서 변화 하였는데 첫번째 순환에서 가장 높았고 순환횟수가 증가함에 따라 감소하였다. 2) 본 실험에서 사용한 출구저항 수준은 출구저항 수준 1에서 요구되는 정백도의 백미를 얻기 위한 순환 횟수는 2회 이었고 출구저항 수준 2에서는 4회 이었는데, 이를 출구저항 수준이 정백압력, 정백율, 완전미수율 및 도정 효율에 가장 큰 영향을 주었다. 3) 스크린에 뚫려있는 슬랏 각도가 $15^{\circ}$에서 $45^{\circ}$로 증가함에 따라서 정백실내의 평균 정백압력은 감소하였고, 완전미수율과 도정 효율은 증가하였으나, 일반적으로 도정수율은 감소하는 경향을 보였다. $-45^{\circ}$의 슬랏 각도를 가진 스크린에서는 슬랏 각도 $15^{\circ}$인 스크린에서와 거의 비슷한 정백압력 수준을 나타냈으나 완전미와 정백미의 생산은 매우 낮았다. 4) 스크린 표면에 기다란 강편 (보통 "띠"라고 부름)을 붙인 원통과 12각형의 스크린에서는 강편을 붙이지 않은 6각형과 8각형 스크린에서 보다는 비교적 높은 정백압력을 나타냈다. 전자는 후자에 비해서 정백효율은 높았으나 완전미수율은 떨어졌다. 5) 정백실내에서 가장 낮은 정백압력을 나타낸 8각형 스크린은 높은 도정수율과 완전미수율을 가져왔으나 상대적으로 정백효율은 낮게 나타났다. 6) 정백실내의 반경 방향의 평균 정백압력($P_R$)과 완전미수율($Y_h$)은 다음과 같은 1차적인 역비례 관계가 있었으며(평균 정백압력 범위는 0.5-0.9kg/$cm^2$), $Y_h=-28.661P_R+84.860$ ($r^2=0.858$) 정백효율($Y_e$)과 정백압력($P_R$) 사이에는 다음과 같은 2차적인 관계가 존재함을 알 수 있었다. $Y_e=-597.5P_{R^2}+929.96P_R-210.15$ ($r^2=0.759$) 정백효율은 정백압력이 0.7-0.8kg/$cm^2$일 때 가장 높았으며, 이때 변이도 가장 심한 것으로 나타났다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.92-100
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• 2018

Vortical systems are considered a main feature to sustain turbulence in a boundary layer through interaction. Such turbulent structures result in frictional drag and erosion or vibration in engineering applications. Research for controlling turbulent flow has been actively carried out, but in order to show the effect of vortices in a turbulent boundary layer, it is necessary to clarify the mechanism by which turbulent energy is transferred. For this purpose, it is convenient to demonstrate and capture phenomena in a laminar boundary layer. Therefore, in this study, the interactions of disturbed flow around a hemisphere on a flat plate in laminar flow were analyzed. In other words, a street of hairpin vortices was generated following a wake region formed after flow separation occurred over a hemisphere. Necklace vortices surrounding the hemisphere also appeared due to a strong adverse pressure gradient that brought high momentum fluid into the wake region thereby leading to an increase in the frequency of hairpin vortices. To mitigate the effect of these necklace vortices, local suction control was applied through a hole in front of the hemisphere. Flow visualization was recorded to qualitatively determine flow modifications, and hot-film measurements quantitatively supported conclusions on how much the power of the hairpin vortices was reduced by local wall suction.

• Fire Science and Engineering
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• v.33 no.4
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• pp.35-40
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• 2019

In this study, the mass flow rate of the heat release rate equation, which is the major factor of the oxygen consumption method, was analyzed for the fundamental investigation of the cone-calorimeter (5 m length and 0.3 m diameter). The shapes of a completely empty inside, 3 mm pore diameter mesh and pore diameter 10 mm honeycomb with 0.76 porosity were constructed using the cone-calorimeter. To calculate the mass flow rate, four bi-directional probes and thermocouples were installed in a uniform position in the vertical direction of flow. The velocity gradient and flow perturbation were measured from the increase in Reynolds number. As the flow capacity increased, the speed gradient increased in all three shapes relative to the turbulence intensity. In addition, the deviation of extended uncertainty to the mass flow was completely low in the order of empty space, mesh (d_p = 3 mm) and honeycomb (d_p = 10 mm and 𝜖 = 0.76) at the 95% confidence level. The results can be used in designs to improve the flow stability of the cone calorimeter.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.529-535
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• 2018

The range extender vehicle runs on a mechanism that allows the small power generation engine to start in the most efficient specific operating range to charge the battery and extend the mileage. In this study, we developed a step motor type intake air supply system that replaces existing throttle body system to develop a simple low cost control logic system. The system was applied to the existing base engine, and in order to improve the performance by increasing the amount of intake air, the effect of changing the length of the intake and exhaust manifold was experimentally examined. As a result, the Type B intake air control actuator operated by one step motor showed higher performance than the Type A in all the operation region, but the performance was lower than that of the base engine due to the increase of flow resistance. To improve this, it was confirmed that the engine performance was improved at both speeds of 2200rpm and 4300rpm when the 140mm adapter was installed in the intake manifold and when the newly designed 70mm exhaust manifold was applied. Through this process, high - precision operation control was realized by connecting the generator load to the optimized engine for the range extender electric vehicle. Experimental results showed that the speed change rate was within ${\pm}2.5%$ at 2200rpm in 1st stage and 4300rpm in 2nd stage and the speed follow-up result of 610 rpm/s was obtained when the speed was increased from 2200rpm to 4300rpm.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.378-383
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• 2013

A butterfly throttle valve has been used to control the brake power of an SI engine by controlling the mass flow-rate of intake air in the induction system. However, the valve has a serious effect on the volumetric efficiency of the engine due to the pressure resistance in the induction system. In this study, a new intake air controlling valve named "Variable Geometry Throttle Valve(VGTV)" is proposed to minimize the pressure resistance in the intake system of an SI engine. The design concept of VGTV is on the application of a venturi nozzle in the air flow path. Instead of change of the butterfly valve angle in the airflow field, the throat width of the VGTV valve is varied with the operating condition of an SI engine. In this numerical study, CFD(computational fluid dynamics) simulation technique was incorporated to have an aerodynamics performance analysis of the two air flow controlling systems; butterfly valve and VGTV and compared the results to know which system has lower pressure resistance in the air intake system. From the result, it was found that VGTV has lower pressure resistance than the butterfly valve. Especially VGTV is effective on the low and medium load operating condition of an SI engine. The averaged pressure resistance of VGTV is about 49.0% lower than the value of the conventional butterfly throttle valve.