• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.765-771
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• 2002

This Paper presents numerical solutions of two-dimensional Euler equations for supersonic steady and unsteady flows with heat addition in a convergent-divergent duct, The Van Leer FVS (flux vector splitting) method in generalized coordinates is employed in order to calculate the inviscid strong shock waves caused by thermal choking. We discuss on transient characteristics, start and unstart phenomena caused by thermal choking, limit of equivalence ratio to avoid thermal choking and fluctuation of specific thrust caused by thermal choking. We prove that thermal choking is a serious problem in view of engine performance.

• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.76-84
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• 2000

A numerical study was conducted for the investigation of thermal choking process in a model scramjet engine based on the experimental results at the Australian National University. The results of numerical simulation showed that thermal choking process could be related to the interaction between hypersonic flow and fuel-air mixing process. Especially, we could make sure that turbulent mixing was most important parameter to the thermal choking process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.684-691
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• 2015

A sudden increase in combustion pressure is observed in the ducted rocket combustion test equipped with pipe shaped and converging nozzle exhaust tubes. This study aims to understand the physical mechanism of abrupt change in combustion pressure using thermal choking in the exhaust tube. Results confirmed that the thermal choking of the flow inside the exhaust tube was responsible for the sudden increase in combustion pressure. Also, high pressure exponent of solid propellants is critical sensitive to the occurrence of thermal choking exhaust pipe. Additionally, numerical simulation showed that the sudden increase in combustion pressure was less possible in diverging pipe because thermal choking is more reluctant to occur.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.80-86
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• 2005

This study presents numerical solutions of the two-dimensional Navier-Stokes equations for supersonic unsteady flow in a convergent-divergent nozzle with heat addition. The TVD scheme in generalized coordinates is employed in order to calculate the moving shock waves caused by thermal choking. We discuss on transient characteristics, start and unstart phenomena, fluctuations of specific thrust caused by thermal choking and viscous effects. We prove that the control of separation of boundary layer is the most important key problem to prevent the thermal choking.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.2 s.257
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• pp.109-115
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• 2007

Airframe-integrated Scramjet engines of NASA Langley type consist of a compressor, a combustion chamber and a nozzle. When some disturbances occur in one module of the engine, its influences are propagated to other modules. In this study, it is investigated numerically how shock waves were caused by thermal choking in one module propagate upstream and how they influence adjacent modules. The calculations are carried out in 2-dimensional supersonic viscous flow model using explicit TVD scheme in generalized coordinates. The adverse pressure gradient caused by heat addition brings about separation of the wall boundary layers and formation of the oblique shock wave that proceed to upstream. This moving shock wave formed one module blocks the flow coming into the adjacent modules, which makes the modules unstarted.

• Journal of Energy Engineering
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• v.21 no.3
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• pp.237-242
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• 2012

This study presents numerical solutions of the two-dimensional Navier-Stokes equations for supersonic unsteady flow in a convergent-divergent nozzle with a isolator. The TVD scheme in generalized coordinates is employed in order to calculate the moving shock waves caused by thermal choking. We discuss on transient characteristics, unstart phenomena, fluctuations of specific thrust caused by thermal choking and effects of isolator. The adverse pressure gradient caused by heat addition brings about separation of the wall boundary layers and formation of the oblique shock wave that proceed to upstream. The proceeding speed of the oblique shock wave to upstream direction for the convergent-divergent nozzle with isolator is lower than that for the nozzle without isolator.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.297-300
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• 2017

A drastic pressure increment at the combustor inlet induced thermal choking is inevitable during scram-to-ramjet transitions. This phenomenon which is called by Non-Allowable Region(NAR) was observed on the excessive increment in the equivalent ratio. However, many studies were not investigated about factors which affects a variation of NAR. In the present study, a variation of NAR with regard to Mach number in the inlet of isolator is numerically and analytically analyzed. The conclusions from the investigation show that increasing the Mach number in the isolator inlet enlarged in the range of NAR.

• Nuclear Engineering and Technology
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• v.47 no.1
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• pp.135-138
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• 2015

A new correlation predicting the idealized critical mass-flow rates of water for subcooled and saturated liquid water including two-phase water flow was developed for a wide range of upstream stagnation pressures (e.g., 0.5-20.0 MPa). A choking correction factor dependent on the upstream stagnation pressure and subcooled temperature was introduced into a new correlation, and its values were suggested to satisfy the idealized nozzle data within 10% error ranges. The suggested correlation will be instructive and helpful for related studies and/or engineering works.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.307-311
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• 2008

Ground test of model Scramjet engine was performed with T4 free-piston shock tunnel at University of Queensland, Australia. Test condition of free stream was Mach 7.6 at 31 km altitude. With this condition, variation effects of fuel equivalence ratio, cavity, cowl setting were investigated. In the results, supersonic combustion or thermal choking was observed depending on the amount of fuel. Cavity and W-shape cowl showed early ignition and enhanced mixing respectively.

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.83-91
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• 2000

A numerical study was carried out to investigate the 'unstart' process of thermally-choked combustion in model scramjet engines. The combustion mechanism of supersonic combustor will be compared with the experimental results obtained from the T3 free-piston shock tunnel at ANU (Australian National University) and the high enthalpy supersonic wind tunnel at UT (University of Tokyo). For the numerical simulation of supersonic combustion. multi-species Navier-Stokes equations were considered. and detailed chemistry reaction mechanism of $H_2$-Air were adopted. The governing equations were solved by Roe's FDS method and LU-SGS method with MUSCL scheme. In this study. it is found that the thermal choking process could result from excessive heat release due to combustion. In detail, sufficient heat release could be generated at local region of very high temperature increased by reflection of shock waves or vortex sheets. Accordingly the flow of downstream of the combustor fell to subsonic field propagated upstream along the combustor. Sometimes the subsonic flow field propagated into isolator could generate precombustion shock waves in the isolator.