• Proceedings of the KSME Conference
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• 2002.08a
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• pp.147-150
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• 2002

In general, a single gas flow through a converging nozzle is choked when the pressure communications between the downstream and upstream flowfields are broken by the sonic condition of Mach number, M=1. A similar phenomenon may occur In two streams of different stagnation properties flowing side by side in a converging nozzle. In this case, the limiting condition of M=1 for flow choking is no longer applied to such a compound compressible flow. The compound choking phenomenon can be explained by means of a compound sound wave at the nozzle exit. In order to detail the flow characteristics involved in such a compound choking of the two streams, the two-dimensional, compressible, Wavier-Stokes equations have been solved using a fully implicit finite volume method and compared with the results of the one-dimensional theoretical analysis. The computational and theoretical results show that the compound sound wave can reasonably explain the compound choking phenomenon of the two streams in the convergent flow channel.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.881-888
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• 2017

In general, the choking phenomenon occurs by flow acceleration for a turbine at high pressure ratio condition. In choking condition, total pressure ratio increases without mass flow rate variation. It is hard to predict choking characteristics by using conventional meanline analysis which used mass flow inlet boundary condition. In the present study, the algorithm for predicting choking point is developed to solve the problem. Moreover, performance estimation algorithm after choking is presented by reflecting the flow behaviour of flow expansion at choked nozzle or rotor. The analysis results are compared with 3D CFD analysis and experimental data to validate present method.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1829-1834
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• 2001

The choking of dual subsonic streams flowing through a convergent duct in contact has been investigated experimentally and theoretically. The experiment was conducted by using blow-down wind tunnel. The condition, when the dual stream flow chocking (compound choking) occurs at the nozzle exit, was explained by one-dimensional analysis of compound sound wave propagation. The experimental results for the condition of compound choking were compared with the prediction from theoretical analysis, and the schlieren optical method using the spark light source has been used to visualize the flowfield.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.54-60
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• 2003

Compound choking frequently occurs at a minimum area of the flow passage, where two or more streams which have different stagnation properties are merged. This phenomenon is especially important in that the flow choking may not be given by Mach number, M=1 at the nozzle throat. In order to obtain a detailed understanding of the flow characteristics involved in the compound flow choking, the two-dimensional, compressible, Wavier-Stokes equations are solved using a fully implicit finite volume method and the predicted solutions are compared with the results of the one-dimensional theoretical analysis. Stagnation pressure and temperature of each stream are changed to investigate the effects on the compound choking. The results show that stagnation pressures of each stream affect Mach number and static pressure distributions downstream of the exit of the convergent nozzle. However, the flow characteristics of the compound choking are not significantly dependent on the total temperature ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.2
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• pp.20-28
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• 2018

In general, the choking phenomenon occurs due to the flow acceleration of a turbine under high pressure-ratio. During choking, the total pressure ratio increases without any variation in the mass flow rate. It is difficult to predict choking characteristics by using conventional meanline analysis, which utilizes mass flow inlet boundary condition. In this study, an algorithm for predicting the choking point is developed to solve this problem. In addition, a performance estimation algorithm is presented to estimate the performance after choking, based on the flow behavior of flow expansion at the choked nozzle or rotor. The analysis results are compared with 3D CFD analysis and experimental data to validate this method.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.4
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• pp.11-18
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• 2006

Compound flow by confluence of two parallel flows through a convergent channel and its choking phenomenon are calculated by one-dimensional isentropic model and completely mixing model. Optical observations and pressure measurements for subsonic/subsonic compound flows are carried out and compared with the results of one-dimensional calculations. As a result, it is found that inlet conditions of one flow influence the behavior of the other flow as well as the choking condition and present experimental data agree well with the results of one-dimensional calculations.

• 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.

• Korean Journal of Bronchoesophagology
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• v.9 no.1
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• pp.83-86
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• 2003

Background and Objectives : Paradoxical vocal cord movement is a series of paroxysmal adduction of the anterior two-thirds of the vocal cords during respiration or during phonation. The choking, stridor, and wheezing in this condition occur primarily on inhalation, rather than on exhalation. The two pathognomonic diagnostic criterias that need to be assessed during an acute presentation are laryngoscopy with direct visualization of paradoxical adduction of the vocal cords and pulmonary function testing. Materials and Methods : A retrospective review of 3 patients who were referred to otolaryngologist from pulmonology department, and were confirmed by typical laryngoscopic findings with paradoxical adduction of the vocal cords was conducted. Results The patients were misdiagnosed as exercised-induced asthma, and unresponsive to corticosteroid and bronchodilators. Improvement was achieved only by diagnosis with paradoxial vocal cord movement. Biofeed back therapy, voice therapy, treatment for reflux laryngitis improved symptoms. Conclusion The etiology of paradoxical vocal cord movement is unknown. It may be functional or emotional. The functional factors that were proposed are neurologic deficit and gastroesophageal reflux. Management methods of this condition consist of psychological counselling, voice therapy, and antireflux medication.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.452-455
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• 2008

Model Scramjet engine is tested with T4 free-piston shock tunnel at University of Queensland, Australia. Basically, test condition is fixed as Mach 7.6 at 31 km altitude. With this condition, variation effects of fuel equivalence ratio, cavity, cowl setting and angle of attack were investigated. In the results, supersonic combustion was observed with low and middle fuel equivalence ratio. At high equivalence ratio, thermal choking was occurred due to the intensive reaction. Cavity and W-shape cowl showed early ignition and enhanced mixing respectively.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.305-310
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• 2001

This paper presents the computational method for analyzing the compressible flow fields in a high voltage gas circuit breaker. There are many difficult problems in analyzing the gas flow in GCB due to complex geometry, moving boundary, shock wave and so on. In particular, the distortion problem of the grid due to the movement of moving parts can be worked out by the fixed grid technique. Numerical simulations are based on a fully implicit finite volume method of the compressible Reynolds-averaged Navier-Stokes equations to obtain the pressure, density, and velocity through the entire interruption process. The presented method is applied to the real circuit breaker model and the pressure in front of the piston is good agreement with the experimental one.