• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.51-58
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• 2020

Research on shock structures of supersonic jet through visualization experiments in low-pressure environment have not been actively conducted. Therefore, in this study, shock waves and supersonic jets were analyzed and compared by numerical analysis and Schlieren technique at low-pressure. Schlieren technique is commonly used to visualize the shock waves generated by density gradient as interferometric methods. Pressure ratio of entrance and ambient was set around 4 to observe moderate under-expanded jet. For validation of experimental and numerical results, the shock structure and frequency were compared. In the case of ST and C nozzle, the results were shown that the difference of shock cell distance was within 10%. The Mach number gradually decreased due to energy reduction, and the error rate was within 7%. D nozzle was not fitted to be observing the shock structure. Because the interface between rarefaction fan and supersonic jet was ambiguous and oscillating phemenoma occurred at end of jet, the supersonic jet in low ambient pressure was observed and analyzed.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.2
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• pp.1-10
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• 2018

Structures, systems and components of nuclear power plants should be able to maintain safety even in the event of design-basis accidents such as high-energy line breaks. The high-pressure steam jet ejected from the broken pipe may cause damage to the adjacent structures. The ANSI/ANS 58.2 code has been adopted as a technical standard for evaluating the jet impingement load. Recently, the U.S. NRC pointed out the non-conservativeness of the ANSI/ANS 58.2, because it does not take into account the blast wave effect, dynamic behavior of the jet, and oversimplifies the shape and load characteristics of the supersonic steam jet. Therefore, it is necessary to improve the evaluation method for the high-energy line break accident. In order to evaluate the behavior of supersonic steam jet, an appropriate numerical analysis technique considering compressible flow effect is needed. In this study, numerical analysis methodology for evaluating supersonic jet impingement load was developed and verified. In addition, the conservativeness of the ANSI/ANS 58.2 model was investigated using the numerical analysis methodology. It is estimated that the ANSI jet model does not sufficiently reflect the physical behavior of under-expanded supersonic steam jet and evaluates the jet impingement load lower than CFD analysis result at certain positions.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.109-112
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• 2002

The supersonic jet discharging from a petal nozzle is known to enhance mixing effect with the surrounding gas because it produces strong longitudinal vortices due to the velocity difference from both the major and minor axes of petal nozzle. In the present study, the supersonic free jet discharging from the petal nozzle is investigated experimentally. The nozzles used are 4, 6, and 8 lobed petal nozzles with a design Mach number of 1.7, and the flow fields are compared with a circular nozzle with the same design Mach number. The pitot impact pressures are measured using a fine pilot probe. The flow fields are visualized using a Schlieren optical method. The results show that the petal nozzle has more increased supersonic length compared with the circular jet.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.525-530
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• 2000

The effects of vortex generators, in the form of small tabs projecting into the flow at the axisymmetric supersonic nozzle exit and triangular thin tapes attached on the inner surface at the nozzle exit, on the characterixtics of supersonic mixing enhancements are experimentally investigated. Delta-shaped tabs as small as 1% of the nozzle exit area produce strong counter-rotating vortices, and is found to produce significant effects on the jet flowfield downstream of the nozzle. The effects is larger on the under-expanded cases than over- and perfect-expanded cases. Nozzle inner surface roughness also can do a role of centerline pressure decay for highly under-expanded jet cases. The effects of the angle of tabs with respect to flow direction are also investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1702-1710
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• 2001

Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.664-669
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• 2001

The characteristics of dual coaxial jet which composed of inner supersonic nozzle of 26500 in constant expansion rate with 1.91 design Mach number and outer converging one with $40^{\circ}$ converging angle with the variation of outer nozzle stagnation pressures are experimentally investigated in this paper. In which the stagnation pressure for the inner supersonic nozzle is 750kPa thus, the inner jet leaving the nozzle is slightly underexpanded. The plenum pressures of outer nozzle are varied from 200 to 600kPa. Flow visualizations by shadowgraph method, impact pressure and centerline static pressure measurements of dual coaxial jet are presented. The results show that the presence of outer jet affects significantly the structures and pressure distributions of inner jet. And outer jet causes Mach disk which does not appear for the case of single jet stream. As the stagnation pressure of outer jet increases, impact pressure undulation is severe, but the average impact pressure keeps high far downstream.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.586-591
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• 2003

The present study addresses experimental results to investigate the effect of the jet supply chamber configuration on the sonic/supersonic swirling jets, as the case study. The experiment is carried out using the convergent nozzle with a various different chamber configurations upstream the nozzle throat, which is composed of four tangential inlet holes for the swirling flows. The jet pressure ratio is varied between 3.0 and 7.0. The sonic/supersonic swirling jet flows are specified by the pitot impact and static pressure measurements and visualized using the Shadowgraph method. The results show that the major structures of the sonic/supersonic swirling jet are strongly influenced by the jet supply chamber.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.15-15
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• 1998

The problem of the impingement of a sonic or a supersonic jet on a flat surface has not only wide applications but has also interesting and very complex flow phenomena. The main applications of this impinging jet include prediction of solid surface erosion, design of launcher systems, stage separation of multi-stage rocket system, V/STOL operations, thermal spray system, and manufacturing technologies of materials. Much have been learned about the supersonic impinging jet flow field but many fundamental questions have not been answered satisfactorily. The problem encompasses many facets of fluid dynamics which, in combination, present the compressibility effect and the viscous-inviscid interaction, coupled with flow separation and reattachment. What is more, there are many flow parameters that have on the impinging jet flow field, for example, Mach number, Reynolds number, pressure ratio, distance between the nozzle exit and flat plate, jet shock structure, nozzle diameter and etc. Thus the existing data on the supersonic impinging jet flow present considerable disagreement in which quantitative comparison between one result and another is often impossible.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.774-779
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• 2008

An experimental study on the micro-supersonic jet flow fields has been carried out. A sonic nozzle of 440 ${\mu}m$-exit diameter and a Laval nozzle of 800 ${\mu}m$ exit diameter with the nozzle exit Mach number 2.0 were fabricated by stretching a micro Pyrex glass tube for the present experiments. Schlieren flow visualization and Pitot pressure distribution of the jet flow field were obtained. Representative characteristics of the jet flow fields such as, supersonic length, jet core length, similarity of the velocity field, and jet spreading rates, have been observed. All the results were compared to previous observations of larger supersonic jets of higher Reynolds numbers, and it was found that overall characteristics of the micro supersonic jet are qualitatively similar as those of the higher Reynolds number jets, except the jet core length and the jet spreading rate.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.2
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• pp.256-262
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• 2001

Viscous solutions of supersonic side jet nozzle and supersonic jet impinging on a flat plate are simulated using three-dimensional Navier-Stokes solver. For rapid and abrupt control of a missile in supersonic flight, side jet on a missile body is found to be a useful devise as evidenced by recent missile development at several nations. The magnitude of the side jet and the duration of it decide the level of control of such a missile system. The aerodynamic characteristics of the side jet devise itself are examined in terms of key parameters such as the side jet nozzle geometry, the chamber pressure and temperature. On the other hand, the jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. As the plate is placed close to the nozzle, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. The amplitude of wall pressure fluctuations subsides as the plate/nozzle distance increases, and the frequency of the wall pressure is estimated on the order of 10.0 KHz. Objectives of this paper are to show accurate simulation of nozzle flow itself and to demonstrate the jet flow structure when the jet interacts with a wall at a close range.