• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.73-81
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• 1997

Numerical analysis on turbulent flow and heat transfer in the rocket nozzle has been studied using the mass-weighted-averaged full Navier-Stokes equations, the Morkovin hypothesis on turbulent flow, the $\textsc{k}$-$\varepsilon$ turbulence model with the wall function specially designed to be able to consider the effects of pressure gradients, heat transfer and compressibility, and the numerical scheme of Karki. The present results are in good agreement with the experiments of Back et al.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.79.2-79.2
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• 2005

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.4
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• pp.328-334
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• 1984

본 연구에서는 기하학적으로는 물론이며 유동 장체가 축대칭이 되고 재순환 영역이 있는 노즐을 제작하여 우선 연구의 1차 단계로서 연소가 없을 경우 시간 평균 유속 및 난류 성분을 레이져 도플러 유속계로 비교적 정밀히 측정한후, 노즐 유체와 주위공기류와의 시간 평균 혼합특성을 구명하기 위하여 가스크로마토그라프에 의하여 농도 분포를 측정, 모델 검토를 위한 기초 데이타 제공과 실험용으로 채용한 노즐류의 구조를 구명하고저 한다. 특히 노즐유체를 수소/질소 혼합기인 경우와 공기를 사용 한 양 경우를 비교, 검토하므로써 부력효과에 대한 평가를 시도하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.9-17
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• 2013

A considerable deal of work has been carried out to get an insight into the gas-solid suspension flows and to specify the particle motion and its influence on the gas flow field. In this paper an attempt is made to develop an analytical model to study the effect of nozzle inlet/exit pressure ratio, particle/gas loading and the particle diameter effect on gas-solid suspension flow. The effect of the particle/gas loading on the mass flow, Mach number, thrust coefficient and static pressure variation through the nozzle is analyzed. The results obtained show that the presence of particles seems to reduce the strength of the shock wave. It is also found that smaller the particle diameter is, bigger will be the velocity as bigger particle will have larger slip velocity. The suspension flow of smaller diameter particles has almost same trend as that of single phase flow with ideal gas as working fluid. Depending on the ambient pressure, the thrust coefficient is found to be higher for larger particle/gas loading or back pressure ratio.

• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.73-80
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• 2014

Drug delivery in human upper airway was studied by the numerical simulation of oral airflow. We created an anatomically accurate upper airway model from CT scan data by using a medical image processing software (Mimics). The upper airway was composed of oral cavity, pharynx, larynx, trachea, and second generations of branches. Thin sliced CT data and meticulous refinement of model surface under the ENT doctor's advice provided more sophisticated nasal cavity models. With this 3D upper airway models, numerical simulation was conducted by ANSYS/FLUENT. The steady inspiratory airflows in that model was solved numerically for the case of flow rate of 250 mL/s with drug-laden spray(Q= 20, 40, 60 mL/s). Optimal parameters for mechanical drug aerosol targeting of predetermined areas was to be computed, for a given representative upper airways. From numerical flow visualization results, as flow-rate of drug-laden spray increases, the drag spray residue in oral cavity was increased and the distribution of drug spray in trachea and branches became more homogeneous.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.249-252
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• 2011

고체로켓추진기관의 추력조절을 위해 핀틀 기술이 사용된다. 아직까지 핀틀 유동에 대해 근본적인 물리적 이해를 돕는 연구가 공개되지 않아, 이 연구에서 다양한 형상의 needle형 핀틀에 따른 유동구조에 대한 수치적 연구를 진행하였다. 2차원 축대칭, 압축성을 고려하여, 상용 열유체 해석 프로그램인 FLUENT 6.2를 사용하여 해석을 수행하였다. 난류 모델을 검증하기 위해 기 수행된 실험 결과와 비교하였다. 핀틀 각도(tip angle)가 작아질수록 노즐에서 유동 박리점이 하류로 이동하며, 핀틀에서 발생하는 끝단 충격파가 약해진다. 핀틀 반경(tip radius)이 작아질수록 핀틀에서 발생하는 끝단 충격파가 하류로 이동하며, 크기는 약해진다. 핀틀 형상(contour)은 유동 박리 지점에 직접적인 영향을 미친다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.116-121
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• 2011

Performance of Secondary Injection Thrust Vector Control system is investigated under various secondary injection operating conditions. 3-dimensional converging-diverging nozzle having 8 secondary injection nozzles is used in this numerical study. Total pressure of flow inside the nozzle is about 70bars, and total temperature set to 300K for cold flow simulation. Effect of secondary injection flow rate and injection nozzle configuration is considered in this research. Simulation is conducted with commercial CFD code Ansys Fluent v13. Spalart-Allmaras(1-equation)model is used for turbulence modeling with AUSM+ scheme. Various performance factors as Axial thrust, side force, system specific impulse ratio are considered and explained for system performance evaluation.

• Journal of the Korean Society of Propulsion Engineers
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• v.26 no.3
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• pp.43-53
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• 2022

In this study, analysis of the flow characteristics of pintle-controlled nozzle with split-line TVC system and the thrust performance prediction was performed. The numerical computation was verified by comparing the thrust coefficient derived from the analysis results with the experimental data. By applying the same numerical analysis technique, the flow characteristics of nozzle were confirmed according to operating altitude, pintle stroke position and TVC angle with the 1/10 scale. As the TVC angle increased, thrust loss occurred and the tendency of AF was different depending on the position of the pintle stroke. Based on the analysis results, the relation of thrust coefficient was derived by applying the response surface methods. The thrust performance model with a slight difference of 1.2% on average from the analysis result was generated.

• Proceedings of the KIEE Conference
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• summer
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• pp.1100-1102
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• 2004

열팽창 방식의 가스차단기는 아크 에너지 자체를 이용하여 압력상승을 얻고, 상승된 압력을 이용하여 전류 영점 부근에서 아크 방향으로의 유동을 형성하여 아크를 소호한다. 대전류 구간에서 노즐 폐색현상이 일어나면 노즐 용삭이 크게 일어나며 용삭된 노즐 물질은 팽창실의 압력과 온도를 상승시키게 된다. 따라서 차단 특성해석을 위해서는 노즐 용삭에 의한 압력 상승해석이 필요하다. 본 논문에서는 아크에너지에 따른 노즐 용삭비를 이용하여 용삭되는 노즐량을 계산하고, 이로 인한 back flow현상을 고려한 해석 방법을 제안한다. 개발된 프로그램을 제작한 차단부 모델에 적용한 결과, 열팽창실의 압력상승치는 시험결과와 잘 일치함을 확인하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.1-8
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• 2014

Overexpanded flow of an axisymmetric thruster nozzle is numerically simulated to investigate effects of nozzle pressure ratio (NPR) on the shock structure and thrust performance. The Reynolds-averaged Navier-Stokes equations with k-${\omega}$ SST turbulence model are solved utilizing FLUENT solver. As the NPR is raised, thrust performance monotonically increases with the shock structure and flow-separation point being pushed toward the nozzle exit. It is also discussed that the flow structure at nozzle-exit plane which is immediately affected by a position of nozzle-interior shocks and expansion waves, has strong influence upon the thrust performance of thruster nozzle.