• 대한기계학회논문집B
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• 제21권5호
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• pp.637-649
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• 1997

Effects of cone angle, pressure-hole orientation and Reynolds number on the five-hole probe calibration have been investigated for eight large-scale conical five-hole probes, which have either perpendicular pressure holes or forward-facing pressure holes for the cone angles of 45 deg, 60 deg, 75 deg and 90.deg. Pitch and yaw angles are changed from -40 deg to +40 deg with an interval of 5 deg, respectively, when the probe Reynolds numbers are 1.77*10$^{4}$, 3.53*10$^{4}$ and 7.06*10$^{4}$. The result shows that larger cone angle results in more sensitive changes in the calibration coefficients. In the case that the cone angle is 45 deg, the pitch-angle and yaw-angle coefficients of the five-hole probe with the perpendicular pressure holes show a very different trend compared with those of the five-hole probe with the forward-facing pressure holes. On the other hand, when the cone angle is more than 60 deg, each calibration coefficient is nearly independent of the pressure-hole orientation. Additionally, the effects of the Reynolds number on the calibration coefficients are also reported in detail.

• 한국유체기계학회 논문집
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• 제14권5호
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• pp.5-11
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• 2011

In this study, the effect of cone angle of seven-hole probe on the accuracy of measured flow angle and velocity has been investigated. The seven-hole probe consisted of seven 1mm OD stainless inner tubes and one 3mm ID stainless tube. Six cone angles of $45^{\circ}$, $60^{\circ}$, $75^{\circ}$, $90^{\circ}$, $105^{\circ}$ and $120^{\circ}$ were tested. Calibrations of the seven-hole probes were conducted within ${\pm}60^{\circ}$ range with the interval of $5^{\circ}$. Analysis results show that the effect on the cone angle was not significant on the accuracy of the measured flow angle, pressure, and velocity. However, the data reduction method had more effect on the measurement accuracy.

• 한국항공운항학회지
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• 제14권1호
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• pp.43-48
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• 2006

The present study was carried out in order to develope a seven-hole pressure probe which is able to measure high flow angles. The seven-hole pressure probe is a non-nulling, directional velocity probe used for measuring three dimensional flow that having high flow angles. A 4 mm diameter seven-hole conical pressure probe was manufactured with a cone angle of 70$^{\circ}$. The probe was comprised of seven 1 mm diameter stainless steel tubes packed close together and fitted into an outer stainless steel sleeve. The calibration procedure is based on the use of the Callington's polynomial curve-fit method. The validity of the seven-hole conical pressure probe is demonstrated by comparisons with hot-wire data.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.23-29
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• 2009

A sand-cone method is commonly used to determine the density of the compacted soils. This method uses a calibration container to determine the bulk-density of the sand for use in the test. The density of the test or compacted soil is computed on the assumption that the calibration container has approximately the same size or volume and allows the sand to fall approximately the same height as a test hole in the field. However, in most cases the size or shape of test hole is not exactly the same as the calibration container. There is certain discrepancy between sand particle settlement or arrangement in the laboratory calibration and in the field testing, which may cause an erroneous determination of in-situ density. The sand filling process is simulated in the laboratory and its effect on the determination of density is investigated. Artificially-made holes with different heights and bottom shapes are prepared to simulate various shapes of the test hole in the field. The sands with different gradations are used in the testing to examine how sand grain size influences the determination of density in the field.

• 한국지반공학회논문집
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• 제31권11호
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• pp.25-31
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• 2015

연속 동하중을 지지하는 철도노반의 탄성거동은 대상 상부노반의 전단탄성계수에 주된 영향을 받으므로, 일정한 다짐도로 조성된 상부노반에서의 전단파속도 획득은 대상 지반의 탄성거동 예측에 활용될 수 있다. 본 연구에서는 상부노반에서 수행된 동적 콘 관입시험(DCPT) 결과로부터 전단파속도($V_s$)를 추정하기 위하여 동적 콘 관입지수(DCPI)와 전단파속도의 상호관계를 제시하고자 하였다. 상호관계의 신뢰도를 확보하기 위하여 동적 콘 관입시험 및 전단파속도 획득은 시공 완료된 철도 상부노반에서 수행되었다. 전단파속도 획득 방법으로서 cross hole 방법이 사용되었으며, 수신기와 발신기의 중간 위치에서 동적 콘 관입시험이 수행되었다. 동일한 심도에서의 동적 콘 관입지수 및 전단파속도 비교 결과, 전단파속도는 결정계수가 0.8 이상인 동적 콘 관입지수의 거듭제곱 형태로 나타났다. 본 연구결과는 동적 콘 관입기를 이용한 상부노반의 강도평가와 동시에 전단파속도 추정 방법으로써 유용하게 사용될 것이라 기대된다.

• 한국분무공학회지
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• 제16권4호
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• pp.201-209
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• 2011

Optimum engine performance is obtained when the spray characteristics is well matched to the geometry of a combustion chamber. Among many parameters governing the combustion performance in internal combustion engine, fuel supply characteristics and atomization are important performance factors. Therefore, spray characteristics of high pressure multi-hole injector has been studied experimentally. An experimental test system has been made to operate high pressure injection system and to visualize spray behavior. Spray visualization has been performed to analyze spray formation, spray cone angle, bent angle and penetration length. Spray interaction with piston has been analyzed with various injector installation angle, injection pressure and ambient pressure. Test results show that penetration length is greatly influenced by the injection pressure. Penetration length is decreased as ambient pressure increased. Spray cone angle is increased as injection pressure and ambient pressure increased. However, bent angle is not influenced by the change of injection pressure and ambient pressure. Spray cone angle distribution map is plotted using the experimental data. Fuel movement around the spark-plug has been enforced as increasing injector installation angle.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.65-71
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• 2002

Characteristics of corona discharge of the different types of the plasma reactors which are cone-hole and cone-plate is investigated experimentally. The discharge starts at lower voltage for the cathode corona than the anode corona and spark occurs at higher voltage for the cathode corona. And the cathode corona makes more stable discharge than the anode corona. The effect of the base gas in corona discharge for different O$_2$/N$_2$ concentrations is related with the gas molecular weight. The discharge for the smaller molecular weight gas occurs easier than for the high molecular weight gas. The discharge current decreases with the increase of oxygen concentration and it increases more sharply for anode corona than for cathode corona as discharge voltage increases after corona onset voltage. NO-NO$_2$ conversion increases with the energy density of corona discharge and the addition of O$_2$ in a base N$_2$ gas.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.73-80
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• 2002

Dimethyl ether (DM) is one of the most attractive alternative fuel far compression ignition engine. Its main advantage in diesel engine application is high efficiency of diesel cycle with soot free combustion though conventional fuel injection system has to be modified due to the intrinsic properties of DME. Experimental study of DME and conventional diesel spray employing a common-rail type fuel injection system with a 5-holes sac type injector (hole diameter 0.168 ㎜/hole) was performed in a high pressure chamber pressurized with nitrogen gas. A CCD camera was employed to capture time series of spray images followed by spray cone angles and penetrations of DME were characterized and compared with those of diesel. Under atmospheric pressure condition, regardless of injection pressure, spray cone angles of the DME were wider than those of diesel and penetrations were shorter due to flash boiling effect. Tip of the DME spray was farmed in mushroom like shape at atmospheric chamber pressure but it was disappeared in higher chamber pressure. On the contrary, spray characteristics of the DME became similar to that of diesel under 3MPa of chamber pressure. Hole-to-hole variation of the DME spray was lower than that of diesel in both atmospheric and 3MPa chamber pressures. At 25MPa and 40MPa of DME injection pressures, regardless of chamber pressure, intermittent DME spray was observed. It was thought that vapor lock inside the injector was generated under the two injection pressures.

• 한국가스학회지
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• 제24권4호
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• pp.25-31
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• 2020

산업용 혹은 발전용 가스터빈에 사용되는 이중 콘형 예혼합 연소기의 연소 특성을 이해하기 위하여 실험적 연구를 수행하였다. 노즐의 여러 연료 분사 방식에 대하여 NOx와 CO의 배출 특성, 화염 안정성 및 연소실 온도 분포에 대한 연소특성을 비교하였다. 주 연구 결과로는 연료홀 개수가 동일하고 연료 홀 직경이 감소하는 경우와 연료 홀면적이 동일하고 연료 홀 수가 감소되는 경우 연료의 연소용 공기층 침투가 커지기 때문에 NOx의 배출은 감소하지만 화염 안정성은 감소하게 된다. 그리고 동일 연료 홀 면적을 이용하는 분사방식에 있어서 연료 홀을 교차 변경하는 경우 연료의 평균 침투거리 증가로 NOx의 배출이 감소되며 연료 침투거리가 적은 연료가 화염을 안정화시키는 역할을 한다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.1052-1055
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• 2001

In micro-drilling of brittle materials including glass, cracks occur at the exit surface. In drilling glass, the main type of crack is cone crack. Cone crack is generated by thrust force acting at the bottom surface of the workpiece. Cone crack size could be reduced by changing cutting conditions, but cone crack still existed. Two methods were proposed to prevent crack formation and perfect hole shapes were obtained. One method is attaching two glass plates with water and the other method is constraining two glass plates. The proposed methods eliminated tensile stress acting on the exit surface of glass and prevented crack propagation.