• Title/Summary/Keyword: 박리 노즐 유동

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Numerical Study of Separated Nozzle Flows for Various Pressure Ratios (압력비에 따른 박리 노즐 유동의 수치적 해석)

  • Kim, Hui-Kyung;Park, Seung-O
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.8
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    • pp.1-9
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    • 2002
  • Axisymmetric separated flows in a converging-diverging conical nozzle are investigated through numerical simulations for various pressure ratios. We employ AUSM scheme for spatial derivatives and Pulliam's 2nd order subiteration time stepping scheme for implicit time integration. Numerical results indicate that the separated flow structures are very complex when compared to the simple quasi-one dimensional flow. Depending on the pressure ratio, the flow within the nozzle is either separated or non-separated. Various separated flow patterns with distinctive features are illustrated and discussed in detail.

Computational Investigation of Pintle Nozzle Flow (핀틀 노즐 유동장의 수치해석적 연구)

  • Kim, Joung-Keun;Lee, Ji-Hyung;Chang, Hong-Been
    • Journal of the Korean Society of Propulsion Engineers
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    • v.13 no.2
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    • pp.35-41
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    • 2009
  • Both the nozzle expansion ratio and the chamber pressure are simultaneously and continuously changed according to pintle movement, resulting in a different internal flow structure and flow separation characteristics. In this paper, the pintle position effect on nozzle flow structure and separation phenomena is analyzed by experimental-aided Computational Fluid Dynamic(CFD). Among the turbulent models for RANS(Reynold Averaged Navier Stokes) in Fluent, Spalart-Allmaras model is better agreement with the nozzle wall pressure distribution attained by cold-flow test than other models. And even if a conical nozzle is used, there is a shock structure similar to cap-shock pattern mainly occurred in contoured or shaped optimized nozzle because of internal shock generated from pintle tip flow separation.

Flow Characteristics of Dual Bell Nozzle with Pintle (핀틀을 적용한 듀얼 벨 노즐의 유동 특성)

  • Kim, Jeonghoon;Heo, Junyoung;Ha, Dongsung
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.379-382
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    • 2017
  • Flow characteristics of dual bell nozzle with pintle were investigated. Thrust and thrust coefficient were compared with the pintle-bell nozzle of the same condition, and difference according to the pintle stroke was investigated. At stroke 0 mm, the thrust of the dual bell nozzle was about 13.18% higher than the bell nozzle, and when the pintle was backward, it was similar to the bell nozzle. The change in expansion ratio with stroke was considered to be more advantageous for a dual bell nozzle that performs altitude compensation through separation and transition.

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Three-dimensional Effects of an Axi-symmetric Pintle Nozzle (축대칭 핀틀노즐의 3차원 효과 분석)

  • Lee, Gang-Min;Sung, Hong-Gye
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.6
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    • pp.47-55
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    • 2018
  • In order to determine whether three-dimensional effects exist in a pintle nozzle of axisymmetric shape, a three-dimensional numerical analysis was performed. The compressibility correction was implemented with the k-${\omega}$ SST turbulence model to predict the complex flow separation transition in acceptable accuracy. Recirculation zones were observed at both the front end and rear faces of the pintle, and the flow through the pintle nozzle conveyed complex shock wave structures. Three-dimensional effects that resulted from the reasonable flow separation location were noted, and a trace of the transient pressure increase was observed, mismatched by a two-dimensional axi-symmetric analysis.

Flow Characteristics of 2 Dimensional Supersonic Nozzle in Overexpanded Conditions (2차원 초음속 노즐의 과대팽창 유동 특성)

  • 김성돈;정인석;최정열
    • Journal of the Korean Society of Propulsion Engineers
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    • v.6 no.2
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    • pp.1-7
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    • 2002
  • In the modern propulsion systems, requited thrust is obtained using a nozzle. Sometimes shock and induced boundary layer separation is generated in an over-expanded convergent-divergent supersonic nozzle. It occurs because the nozzle expansion ratio is too large for a given nozzle pressure ratio (NPR). This phenomenon can be explained that it redefines effective nozzle geometry, shorer nozzle geometry and lower pressure ratio, in a given pressure ratio. Numerical studies were conducted about a fixed geometry 2D nozzle in overexpanded condition and compared with Hunter's experimental result. For the numerical simulation of the supersonic nozzle, Navier-Stokes equations are considered and as a turbulent model, $\kappa$-$\varepsilon$ /$\kappa$-$\omega$ blended SST two equation turbulent model is used. The characteristics of $\lambda$-shape shock systems due to the interaction of shock and boundary layer was investigated in a low NPR. And the result of comparison of thrust value shows that a fixed geometry nozzle can cover required flight mission.

Compressibility Correction Effects of Two-equation Turbulence Models for a Supersonic Through-type Pintle Nozzle with Large Scale Separation Flow (큰 박리유동을 동반한 초음속 관통형 핀틀노즐 유동에 적합한 2-방정식 난류모델의 압축성계수 보정 영향)

  • Heo, Junyoung;Jung, Junyoung;Sung, Hong-Gye;Yang, June-Seo;Lee, Ji-Hyung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.1
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    • pp.61-69
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    • 2013
  • Numerical simulations have been performed for assessment of compressibility correction of two-equation turbulent models suitable for large scale separation flows perturbed by a pintle strokes. Two-equation turbulence models, the low Reynolds k-${\varepsilon}$ and the k-${\omega}$ SST models with or without compressibility correction proposed by Wilcox and Sarkar are evaluated. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. Mach disk location and pressure recovery profiles in flow separation region are noticeably distinct between turbulent models of k-${\varepsilon}$ and k-${\omega}$ SST. The compressible effect corrections to those models improve resolving of separation flow behaviors. The compressibility corrections to k-${\varepsilon}$ model have provided very comparable results with test data.

Thrust Characteristics of Through-type Pintle Nozzle at Operating Altitudes Conditions (작동 고도에 따른 관통형 핀틀 노즐의 추력 특성 연구)

  • Jeong, Kiyeon;Hong, Ji-Seok;Heo, Junyoung;Sung, Hong-Gye;Yang, Juneseo;Ha, Dongsung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.20 no.4
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    • pp.59-67
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    • 2016
  • Numerical simulations have been performed to investigate thrust characteristics of a through-type pintle nozzle with or without flow separation at various operating altitudes. The low Reynolds number $k-{\varepsilon}$ with compressibility correction proposed by Sarkar are applied. The detail flow structures are observed and static pressures along nozzle wall are compared with experimental results. The flow separation in the pintle nozzle disappears and jet plume strongly expands as its operating altitude increases. To evaluate the thrust characteristics, the momentum term and pressure term of thrust are analyzed. Thrust and thrust coefficient at altitude 20 km are about 10% more than them at the ground 0km.

Study of Characteristics of Assist Gas in Laser Machining Using Flow Visualization Techniques (유동가시화 기법을 이용한 레이저가공의 보조가스 충돌특성에 관한 연구)

  • Son, Sang-Hyuk;Lee, Yeol;Min, Seong-Kyu
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.2
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    • pp.153-160
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    • 2011
  • The characteristics of supersonic coaxial/off-axis jet impingements on a slanted kerf surface were experimentally studied, to investigate the role of the assist gas that removes molten materials from cut zone formed by laser machining. In this parametric study, hundreds of high-resolution schlieren images were obtained for various gas pressures, distances between nozzle exit and kerf surface, kerf widths, and alignments of off-axis nozzle. It was noticed that simply increasing the assist gas pressure was not effective in eliminating the flow separation that occurs downstream of the kerf surface. However, it was also observed that by increasing the kerf width and utilizing off-axis nozzles, the separation of the assist gas on the kerf surface can be weakened. The effect of the distance between the nozzle exit and the kerf surface on the characteristics of separation occurring on the kerf surface was found to be lower in the case of supersonic nozzles than that in the case of sonic nozzles.

A Numerical Study on Effects of Displacement of a Variable Area Nozzle on Flow and Thrust in a Jet Engine (가변노즐의 변위가 제트 엔진의 유동 및 추력특성에 미치는 영향에 관한 수치해석)

  • Park, Junho;Sohn, Chae Hoon;Park, Dong Chang
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.5
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    • pp.1-9
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    • 2013
  • Variable area nozzle, where both throat and exit area vary, is required for optimal expansion and optimal nozzle shape upon operation of after-burner. Steady-state and transient analyses are carried out for each condition with and without afterburner operation and as a function of the location of the nozzle flap. Effects of that nozzle displacement on flow and thrust characteristics are analyzed from numerical results. With variable area nozzle adopted, the combustion field is variable in time, leading to periodically variable thrust. For off-design conditions, flow separation shows up due to over expansion at the flap tips and shock wave does in the nozzle due to under expansion. The undesirable phenomena can be solved by control of variable area nozzle.

Numerical Analysis of Flow Characteristics within Blades for Design Parameters of Impulse Supersonic Turbine Blade (충동형 초음속 터빈 익렬의 설계 변수에 따른 익렬내 유동 특성에 관한 수치적 연구)

  • 신봉근;정수인;김귀순;이은석
    • Journal of the Korean Society of Propulsion Engineers
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    • v.8 no.2
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    • pp.62-72
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    • 2004
  • In this paper. firstly, numerical results were compared with experimental results to verify accuracy of the results. It is found that the numerical results show good agreements with experimental result. Next, computations about flow within blades for design parameters such as radius of the pressure and suction side's curvature and pitch-chord ratio have been performed. It is found that the flow and performance characteristics mainly depend on shocks occurred at the leading edge of blades and the end of nozzle and separations occurred inside the flow passage. And shock of nozzle and separations depend upon area of flow passage and shocks of blade are affected by the number of blades occupied by a nozzle.