• 한국연소학회지
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• 제7권1호
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• pp.1-7
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• 2002

Experiments have been performed to investigate the structure of axisymmetric hydrogen diffusion flame in a supersonic coflow air. The characteristics and structure of supersonic flames are compared with those of subsonic flames as the velocity of coflow air increases from subsonic to supersonic velocity of Mach 1.8. Also, the subsonic and supersonic flow fields are analyzed numerically for the non-reacting conditions and the possible flame contours indicated by fuel mass fraction are compared with the measured OH radical distributions. It is found that the flame structure indicates more like a partially premixed flame as the coflow air velocity is increased from subsonic to supersonic regimes; strong reaction zone indicated by intense OH signal is found at the center, which is different from subsonic flame cases. And it is shown that the fuel jet passes along the recirculation zones behind the bluff-body fuel nozzle resulting in relatively long mixing time. This is believed to be the reason of the partially premixed flame characteristics found in the present supersonic flames.

• 한국항공우주학회지
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• 제35권1호
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• pp.27-32
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• 2007

본 논문에서는 초음속 제트로부터 유발되는 소음의 특성을 실험적으로 분석하고, 기존의 소음예측식을 사용하여 비교해 봄으로서 예측식의 적용가능 범위를 살펴보았다. 실험을 위하여 제작된 초음속제트 발생장치의 출구마하수를 측정하기 위하여 정체실의 온도, 압력과 함께 피토 튜브를 이용하였고, 결과를 쉐도우 그래프 가시화 방법을 사용하여 얻은 결과와 비교하였다. 제트소음의 스펙트럼을 관찰한 결과, 불완전 팽창의 제트 유동에서 발생하는 충격파 관련 소음인 광대역 소음과 스크리치 톤 소음의 경향이 나타는 것을 확인 할 수 있었다. 아음속 조건에서는 큰 난류 구조에 의해 발생되는 난류 혼합 소음에 의하여 흐름방향으로 강한 방향성을 나타내었고, 초음속 조건에서는 충격파 관련 소음이 흐름의 상류 방향으로도 강하게 전파됨을 확인 하였다. 그리고 제트 엔진의 소음 예측 프로그램인 ARP876D 코드를 이용하여 실험에서 측정한 스펙트럼과 비교해 본 결과 아음속 영역에서보다는 초음속 영역에서 더 좋은 결과를 보였다.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• 한국군사과학기술학회지
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• 제20권3호
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• pp.393-404
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• 2017

Side jet effect on the aerodynamic characteristics of a missile was investigated using experimental and computational methods. A couple of side jets were injected toward outward downstream at mid point of missile body. Cold air jet was used in the wind tunnel test, and cold and hot jet were used in the computation. Wind tunnel test was carried out with jet and without jet, and calculation was performed for three cases ; no jet, cold air jet, and hot mixture gas jet. From the comparison of measured and calculated data for all cases, two points could be deduced. Firstly, side jet made static stability to be unstable by increasing body normal force near the side jet exit and by decreasing tail normal force. Secondly, hot mixture gas had more significant effect on the static stability of a missile-type body than cold air jet.

• 한국소음진동공학회논문집
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• 제14권1호
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• pp.50-55
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• 2004

In this study, slit-tones by plane impinging jet are investigated experimentally over the whole subsonic flow range, especially at low speeds, in order to obtain the instability behaviour of impinging plane jet. Slit-tones are generated at low speeds associated with laminar shear layer instability as well as at high speeds associated with turbulent instability. Most of low-speed slit-tones are induced by symmetric mode instability unless the slit is not so wide, in which case antisymmetric modes are induced like edge-tones. It is found that the frequencies at low speeds ate controled by the unstable condition of the vortex at the nozzle exit and its pairings by which the frequencies are decreased by half. In the case of symmetric modes related with low-speed slit-tones, frequencies lower than those associated with one-step pairings are not found.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.502-507
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• 2003

Spiral jet is characterized by a wide region of the free vortex flow with a steep axial velocity gradient, while swirl jet is largely governed by the forced vortex flow and has a very low axial velocity at the jet axis. However, detailed generation mechanism of spiral flow components is not well understood, although the spiral jet is extensively applied in a variety of industrial field. In general, it is known that spiral jet is generated by the radial flow injection through an annular slit which is installed at the inlet of convergent nozzle. The objective of the present study is to understand the flow characteristics of the spiral jet, using a computational method. A finite volume scheme is used to solve 3-dimensional Navier-Stokes equations with RNG ${\kappa}-{\varepsilon}$ turbulent model. The computational results are validated by the previous experimental data. It is found that the spiral jet is generated by coanda effect at the inlet of the convergent nozzle and its fundamental features are dependent the pressure ratio of the radial flow through the annular slit and the coanda wall curvature.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.65.2-65.2
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• 2005

• 한국분무공학회지
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• 제14권2호
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• pp.59-64
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• 2009

These experiments are close examination of spray characteristics that are continuous liquid jet and modulated liquid jet. The experiments were conducted using water, over a range of crossflow velocities from $42{\sim}l36\;m/s$, with modulation frequencies of $35.7{\sim}166.2\;Hz$. Between continuous crossflow jet and modulated cross-flow jet of penetration, breakup point, spray angle and macro spray shape are experimentally investigated with image analysis. In cross-flow field, main parameter of liquid jet for breakup was cross-flow stream rather than modulation effect. As oscillation of the periodic pressure that could make liquid jet moved up and down, the mixing efficiency was increased. Also, a bulk of liquid jet puff was detected at upper field of liquid surface. So, this phenomenon has a good advantage of mixing spray from concentration of center area to outer area. Because of modulation frequency, SMD inclination of the structured layer was evanescent. Cross-sectional characteristics of SMD at downstream area were non-structured distributions. Then cross-sectional characteristics of SMD size were about same tendency over a range that is effect of spray mixing. The tendency of volume flux value for various modulation frequency was same distribution. And volume flux was decreased when the modulation frequency increase.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.1210-1216
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• 2001

The impinging tones by high-speed plane jets are investigated for the characteristics of edgetone generation based on experimental observations. Experiment has been performed for edgetones with a slit nozzle and a wedge system. The jet in the experiment is varied from low to high subsonic speed to obtain the effect of the speed on the frequency characteristics of impinging tones. The experimental data obtained previously for edgetones and platetones by various nozzles are compared with the present edgetone data for the condition of tone generation, the frequency ranges and the effective source point. It is found that the jet speed has no fundamental influence on the impinging tone characteristics. Regardless of the jet speed, the effective source point is about a quarter wavelength downstream from the edge tip. With increase in jet speed, the influence of the nozzle configuration is decreased and the operating frequencies show good coincidencies by normalized parameters based on the slit thickness.

• 한국추진공학회지
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• 제4권4호
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• pp.1-8
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• 2000

본 연구에서는 아음속/초음속 이젝터 시스템의 효과적인 설계를 목적으로, 증기 보일러로부터 발생하는 파열증기를 1차 구동유체로 하는 축대칭 아음속/초음속 이젝터 유동을 실험하였다. 과열증기는 여러형태의 아음속/초음속 노즐에 의하여 이젝터 혼합부로 방출되도록 설계되었으며, 2차정체실 내부에 있는 대기 공기는 증기제트에 의하여 혼합부로 유입된다. 실험에서는 2차정체실의 진공성능을 조사하기 위하여 넓은 범위의 이젝터 자동압력비에 대하여 적용하였다. 본 연구의 결과로부터 이젝터목에서 혼한유동의 정압은 1차 노즐의 형태에 관계없이 이젝터 작동압력비의 함수만에 의하여 결정된다는 것을 알았다.