• Title/Summary/Keyword: Nozzle L/D

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Wavenumber analyses of panel vibrations induced by transonic wall-bounded jet flow from an upstream high aspect ratio rectangular nozzle

  • Hambric, Stephen A.;Shaw, Matthew D.;Campbell, Robert L.
    • Advances in aircraft and spacecraft science
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    • v.6 no.6
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    • pp.515-528
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    • 2019
  • The structural vibrations of a flat plate induced by fluctuating wall pressures within wall-bounded transonic jet flow downstream of a high-aspect ratio rectangular nozzle are simulated. The wall pressures are calculated using Hybrid RANS/LES CFD, where LES models the large-scale turbulence in the shear layers downstream of the nozzle. The structural vibrations are computed using modes from a finite element model and a time-domain forced response calculation methodology. At low flow speeds, the convecting turbulence in the shear layers loads the plate in a manner similar to that of turbulent boundary layer flow. However, at high nozzle pressure ratio discharge conditions the flow over the panel becomes transonic, and the shear layer turbulence scatters from shock cells just downstream of the nozzle, generating backward traveling low frequency surface pressure loads that also drive the plate. The structural mode shapes and subsonic and transonic surface pressure fields are transformed to wavenumber space to better understand the nature of the loading distributions and individual modal responses. Modes with wavenumber distributions which align well with those of the pressure field respond strongly. Negative wavenumber loading components are clearly visible in the transforms of the supersonic flow wall pressures near the nozzle, indicating backward propagating pressure fields. In those cases the modal joint acceptances include significant contributions from negative wavenumber terms.

Effect of AC Electric Field on Decreasing Liftoff Height in Laminar Lifted Jet Flames (층류 부상 화염의 화염부상 높이 감소 구간에서 교류 전기장이 인가된 화염에 관한 영향)

  • Seo, B.H.;Van, K.H.;Kim, G.T.;Park, J.;Keel, S.I.;Kim, S.W.;Chung, S.H.
    • Journal of the Korean Society of Combustion
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    • v.22 no.3
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    • pp.17-22
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    • 2017
  • An experimental study has been conducted to elucidate the effect of AC electric field on behaviors of laminar lifted flame in nitrogen-diluted methane coflow-jets. Our concerns are focued on the regime to show a decrease in liftoff height, $H_L$ with increasing nozzle exit velocity, $U_O$ (hereafter, $decreasing-H_L$). The $H_L$ with $U_O$ near flame extinction were measured by varying the applied AC voltage, $V_{AC}$ and frequency, $f_{AC}$ in a single electrode configuration. The behavior of $H_L$ with a functional dependency of $V_{AC}$ and $f_{AC}$ was categorized into two regime : (I) $H_L$ decreased for nozzle diameter, D = 1.0 mm, and (II) $H_L$ increased in the increase of $f_{AC}$ for a fixed $V_{AC}$ in a D = 4.0, 8.4 mm. The lifted flames in $decreasing-H_L$ region was unstable in high voltage regimes while the $H_L$ showed a decreasing tendency with $U_O$ except them. Such behaviors in $H_L$ were also characterized by functional dependencies of related physical parameters such as $V_{AC}$, $f_{AC}$, $U_O$, fuel mole fraction ($X_{F.O}$) and D.

Experimental Study of High-Altitude Simulation using Small-Scale Supersonic Diffuser (소형 초음속 디퓨저를 이용한 고고도환경 모사에 대한 시험적 연구)

  • Lee Ji-Hyung;Oh Jong-Yun;Byun Jong-Ryul
    • Journal of the Korea Institute of Military Science and Technology
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    • v.7 no.4 s.19
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    • pp.138-145
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    • 2004
  • Experimental study was conducted on cylindrical supersonic diffuser in order to investigate the effects of the ratios of diffuser area to nozzle throat area (Ad/At), diffuser area to nozzle exit area (Ad/Ae), nozzle exit area to its throat area (Ae/At), and diffuser length to its diameter (L/D), the free volume of vacuum chamber, and the relative distance between nozzle exit and diffuser inlet on the diffuser performance. The study showed that the minimum diffuser starting pressure (Po/Pa)st increased monotonically with increase in (Ad/At) as predicted by the normal shock and momentum theory models and the volume of vacuum chamber affected vacuum pressure level during diffuser operation at lower value of (Ad/Ae). The results of this investigation will be utilized in the design of real-scale high-altitude simulation test facility.

Experimental Study on the Flow Characteristics of High Pressurized Jets Depending upon Aspect Ratio (노즐 형상비에 따른 고압 분사류의 유동특성에 관한 실험적 연구)

  • Namkung J.H.;Lee S.J.;Kim K.C.;Lee S.G.;Rho B.J.
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.233-236
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    • 2002
  • The high-pressurized spray nozzle is used f3r special washing and cutting with strong impact force. The performance of this nozzle, which focused on spray penetration and radial dispersion, was mainly investigated to maximize the momentum and minimize the flow loss. Hence, our experimental research was conducted by changing the aspect ratio ranging from 0 to 3 with nozzle outlet of 1.1. The spray trajectory far high-pressurized water was experimentally investigated using PDPA diagnostics, which was available at spray downstream region. As the spray at upstream near the nozzle exit did not show the improved disintegration. The results showed empirical correlation with regard to non-dimensional axial velocity distribution, spray penetration, and radial spreading rate with photographic visualization.

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An Experimental Study on the Characteristics of Gas Burner Nozzle (가스버너의 노즐특성에 관한 실험적 연구)

  • Chung, D.H.;Kim, W.B.;Dong, S.K.
    • 한국연소학회:학술대회논문집
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    • 1995.06a
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    • pp.105-121
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    • 1995
  • The objective of this study is to find out the design data for gas burner with an axal and radial type nozzles. The design parameters are chosen as the stabilizer type, the jet hole size of gas nozzle, the distance between gas nozzle and stabilizer, the size of stabilizer and the hole size of stabilizer, the stabilizer type with or without air swirler, the angle of swirler. For the experimental test combustor sizing ${\phi}1.3m{\times}L4.5m$ is designed and manufactured, in which the set up of power diagram, the exhaust gas analysis, blow-off test, the flame temperature and the direct photography are performed.

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Cooling Characteristics of a Hot Steel Plate by a Circular Impinging Liquid Jet (원형수직 충돌 수분류에 의한 고온강판의 냉각특성 연구)

  • 오승묵;이상준
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.6
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    • pp.1150-1155
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    • 1992
  • The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

Prediction of the Mechanical Erosion Rate Decrement for Carbon-Composite Nozzle by using the Nano-Size Additive Aluminum Particle (나노 알루미늄 입자 첨가 추진제에 의한 탄소복합재 노즐의 기계적 삭마 감소 특성 예측)

  • Tarey, Prashant;Kim, Jaiho;Levitas, Valeny I.;Ha, Dongsung;Park, Jae Hyun;Yang, Heesung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.19 no.6
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    • pp.42-53
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    • 2015
  • In this study, the influence of Al particle size, as an additive for solid propellant, on the mechanical erosion of the carbon-composite nozzle was evaluated. A new model which can predict the size and distribution of the agglomerated reaction product($Al(l)/Al_2O_3(l)$) was established, and the size of agglomerate were calculated according to the various initial size of Al in the solid propellant. With predicted results of the model, subsequently, the characteristics of mechanical erosion on the carbon-composite nozzle was estimated using a commercial CFD software, STAR CCM+. The result shows that the smaller the initial Al particles are, in the solid propellant, the lower is the mechanical erosion rate of the composite nozzle wall, especially for the nano-size Al particle.

Concave surface curvature effect on heat transfer from a turbulent round impinging jet (오목표면곡률이 난류원형충돌제트의 열전달에 미치는영향)

  • Im, Gyeong-Bin;Lee, Dae-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.5
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    • pp.691-699
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    • 1997
  • The effects of concave hemispherical surface curvature on the local heat transfer from a turbulent round impinging jet were experimentally investigated. The liquid crystal transient method was used for these measurements. This method, which is a variation on the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystals for the measurement of the surface temperature. The Reynolds number ranges from Re=11,000 to 50,000, the nozzle-to- surface distance from L/d=2 to 10, and the surface curvature from D/d=6 to 12.The present results are also compared to those for the flat plate case. In the experiment, the local Nusselt numbers tend to increase in all regions with an increasing surface curvature. The maximum Nusselt number for all Reynolds numbers occurred at L/d .ident. 6 and a second maximum in the Nusselt number occurred at R/d .ident. 2 for both Re=23,000 and Re=50,000 in the case of L/d=2 and for Re=50,000 only in the case of L/d=4. Meanwhile, as the surface curvature increases, the value of the secondary maximum Nusselt number decreases. All the other cases exhibit monotonically decreasing values of the Nusselt number along the curved surface. The stagnation point Nusselt numbers are well correlated with Re, L/d, and D/d.

Control of Impinging Jet Heat Transfer Using Mesh Screens (메쉬 스크린을 이용한 충돌제트 열전달 제어에 관한 연구)

  • Jo, Jeong-Won;Lee, Sang-Jun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.5
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    • pp.722-730
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    • 2001
  • The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.

Numerical Analysis on Development of Nozzle Shape for NOVEC Gas Extinguishing System (NOVEC가스 소화설비용 노즐 형상 설계에 대한 수치해석)

  • Yun, Jeong In;Jung, Kyung Kuk;Kim, Ji Sung;Kim, Sung Yoon;Rho, Beom-Seok;Choi, Jae-Hyuk
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.24 no.7
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    • pp.939-944
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    • 2018
  • Clean fire extinguishing agents refer to chemical that can replace Halon 1211 and Halon 1310 according to the Montreal Protocol fermented to protect the Earth's ozone layer. In Korea and abroad, system standardization and performance evaluation of clean fire extinguishing agents are being carried out. This paper proposes an optimal nozzle shape by modeling and numerical analysis of various nozzle shapes based on general clean fire extinguishing system. The ejection speed of the nozzle can be improved by studying three - dimensional modeling of the nozzle for two shapes, Type A and B. Flow analysis was performed on the two types of nozzles and the gas velocity and pressure distribution were measured with different nozzle diameters. It was confirmed that the jetting speed was changed at the nozzle outlet according to the number and diameter of the nozzle holes. The flow rate increased with increasing the pressure regardless of the nozzle hole diameter. Based on the results obtained from the experiment, the K-factor value was deduced. Finally, a nozzle with a 12-hole structure with a 5-mm nozzle hole was proposed.