• Title/Summary/Keyword: Jet Oscillation

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A Study on Self-excitations in Laminar Coflow Jet Flames (층류 동축류 제트화염에서의 화염진동에 관한 실험적 연구)

  • Yoon, Sung Hwan;Park, Jeong;Yun, Jin Han;Keel, San In;Kwon, Oh Boong
    • 한국연소학회:학술대회논문집
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    • 2012.04a
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    • pp.83-85
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    • 2012
  • Experimental study in coflow jet flames has been conducted to investigate the effects of adding $N_2$, $CO_2$ and He to coflowing air-side in self-excitations. Differences in the behaviors between buoyancy-driven and diffusive-thermal self-excitations with similar frequency range are explored and discussed in laminar coflow jet flames.

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Prediction of Supersonic Jet Impingement on Flat Plate and Its Application (초음속 충돌제트에 대한 수치적 연구와 응용)

  • Lee K. S.;Hong S. K.;Park S. O.;Bae Y. S.
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.225-228
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    • 2002
  • Supersonic jet impingement on a flat plate has been investigated to show the flow physics for different jet heights and to demonstrate the adequacy of the characteristics-based flux-difference Wavier-Stokes code Current study also compares the steady-state solutions obtained with variable CFL number for different grid spacing with the time-accurate unsteady solutions using the inner iterations, displaying a good agreement between the two sets of numerical solutions. The unsteady nature of wall fluctuations due to bouncing of the plate shock is also uncovered for high pressure ratios. The methodology is then applied to a complex vertical launcher system where the jet plume hits the bottom wail, deflects into the plenum and eventually exits through the vertical uptake. Flow structures within vertical launcher system are captured and solutions are partially verified against the flight test data. Present jet impingement study thus shows the usefulness of CFD in designing a complex structure and predicting flow behavior within such a system.

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EFFICIENT SIMULATION AND SCALING OF OSCILLATORY IMPINGING JETS (진동하는 충돌 제트의 스케일링과 효율적인 수치 모사)

  • Kim S. I.;Park S. O.;Hong S. K.;Lee K. S.
    • Journal of computational fluids engineering
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    • v.10 no.4 s.31
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    • pp.32-38
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    • 2005
  • Present study simulates oscillatory supersonic impinging jet flows using the axisymmetric Navier-Stokes code. To capture the salient features of flow oscillation and overcome the divergence during the initial transient period, several tests have been conducted for the grid and time step sizes. The results also show that the effects of the inlet flow condition at the nozzle exit and turbulence on the oscillatory behavior of supersonic impinging jets are negligible. Frequencies of the surface pressure oscillation obtained by the selected numerical method are in good accord with the measured impinging tones for various cases of nozzle-to-plate distance. Two seemingly different staging behaviors with nozzle-to-plate distance and nozzle pressure variations are found to correlate well if the frequency and distance are normalized by the length of the first shock cell.

An Experimental Study on the Screech Tone in Supersonic Jet (초음속 제트의 스크리치 톤에 관한 실험적 연구)

  • Lim, Chae-Min;Kwon, Yong-Hun;Aoki, Toshiyuki;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.2023-2028
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    • 2004
  • The effects of nozzle-lip thickness on the relationship between screech tone and broadband shock-associated noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. A baffle plate was installed at the exit of the nozzle and its size was varied to obtain different nozzle-lip thicknesses. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained clearly show that the screech tones are influenced by the nozzle-lip thickness. It is found that the screech tone and its peak amplitude are strongly dependent on whether the jet is over-expanded and under-expanded at the nozzle exit.

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Numerical Study of Laminar Flow in a Combustor with a Planar Fuel Jet (Planar-Jet형 연소내 층류유동의 전산해석)

  • Eom, Jun-Seok;Kim, Do-Hyeong;Yang, Gyeong-Su;Sin, Dong-Sin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.12
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    • pp.1644-1651
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    • 2000
  • In this study, the confined laminar flow and transport around a square cylinder with a planar fuel jet are numerically simulated. Both rear and front jets are considered, respectively. In each case, various ratios of the jet velocity to the fixed upstream velocity are taken into consideration. In case of the rear jet, the high mass-fraction region is formed along the streamlines from the jet exit, and the oscillation of the force on the square cylinder eventually disappears as the jet velocity is close to the upstream velocity. In case of the front jet, drag is significantly reduced when the jet velocity ratio is grater than 1. The results obtained exhibit flow and scalar-mixing charactered in a planar combustor.

Experimental Study on Characteristics of Steam Condensation in a Sub-cooled Water Pool (과냉각수조에서 증기응축 특성에 관한 실험적 연구)

  • Kim, Hwan-Yeol;Cho, Seok;Song, Chul-Hwa;Chung, Moon-Ki;Choi, Sang-Min
    • Journal of Energy Engineering
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    • v.8 no.2
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    • pp.298-308
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    • 1999
  • Experimental study on characteristics of direct contact condensation of steam discharged into a sub-cooled water pool has been performed using five different sizes of horizontal nozzle over a wide range of steam mass fluxes and pool temperatures. Steam condensation phenomena have been observed visually and by taking pictures of steam jets using a high speed video camera. Two different steam jet shapes such as ellipsoidal shape and conical shape were typically observed for a stable steam jet, depending on the steam mass flux and pool temperature. The steam jet expansion ratio and the steam jet length as well as the condensation heat transfer coefficients were determined. The effect of steam mass flux, pool temperature, and nozzle diameter on these parameters were also discussed. Empirical correlations for the steam jet lengths and the condensation heat transfer coefficients as a function of steam mass flux and condensation driving potential were established. The axial and radial temperature distributions in steam jet and in surrounding water were measured. The effect of steam mass flux, pool temperature, and nozzle diameter were also discussed. The condensation regime map, which consists of six regimes such as chugging, transient chugging, condensation oscillation, stable condensation, bubble condensation oscillation, and intermittent oscillation condensation, were established. In addition, the dynamic pressures at the pool wall were measured. The close relation of dynamic pressure and steam condensation mode, which is also dependent on steam mass flux and pool temperature, was found.

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Glow Discharge as Detector for Gas Chromatography (글로우방전을 이용한 가스크로마토그라프 검출기의 개발)

  • 김효진;박일영;장성기;김박광;박만기
    • YAKHAK HOEJI
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    • v.37 no.1
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    • pp.76-83
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    • 1993
  • The changes in discharge current, emission and/or oscillation frequency of the electric oscillation of a glow discharge are the potential sensitive measure of the concentration of an impurity in the argon plasma supporting gas. A single jet enhanced glow discharge has been interfaced with the gas chromatograph via 1/8" O.D. tube with a heating pad to study the changes in discharge current. To investigate the optimum operating conditions of the glow discharge system as detector for gas chromatography, pressure, gas flow rate, discharge current, distance between the anode and the cathode have been studied.

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Spray Characteristics of a Pulsed Liquid Jet into a Cross-flow of Air (아음속 횡단 유동장으로 펄스 분사된 액체 제트의 분무특성)

  • Lee, In-Chul;Byun, Young-Wu;Koo, Ja-Ye
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.61-64
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    • 2008
  • The present study of these experiments are close examination of spray characteristics that are continuous liquid jet and modulated pressure pulse liquid jet. The experiments were conducted using water, over a range of cross-flow velocities from 42${\sim}$136 m/s, with injection frequencies of 35.7${\sim}$166.2 Hz. Between continuous cross-flow jet and pressure pulsed cross-flow jet for characteristics of penetration, breakup point, spray angle and macro spray shape are investigated experimentally. In cross-flow field, main parameter of liquid jet for breakup was cross-flow stream rather than pressure pulse frequency. 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 pressure pulsation frequency, an inclination of SMD for 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 frequency of pressure pulse was same distribution. And volume flux was decreased when the frequency of pressure pulse increase.

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