• Title/Summary/Keyword: Oblique shock

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The Interaction Between Modules Caused by Thermal Choking in a Supersonic Duct (덕트내 초음속 유동에서 열폐색에 의한 모듈 간의 간섭)

  • Kim, Jang-Woo;Koo, Kyung-Wan;Han, Chang-Suk
    • 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.

Plume Structure Analysis of an Axisymmetric Supersonic Micro-nozzle at the Various Pressure Ratios (압력비가 변할 때 축대칭 초음속 노즐의 플룸 구조 해석)

  • Kwon, Soon-Duk;Kim, Sung-Cho;Kim, Jeong-Soo;Choi, Jong-Wook;Kim, Yong-Sseok
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2862-2867
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    • 2007
  • The steady non-reacted compressible flow field in a symmetric micro-thruster, which is used for the accurate attitude control of a satellite, is analyzed varying the nozzle pressure ratio (NPR) to investigate the plume characteristics. The nozzle throat diameter is 0.06 inch and the area ratio is 56. The recirculation region is found just behind the normal shock at the several NPRs due to the locally adverse pressure gradient along the nozzle centerline when the environmental pressure is atmospheric. This phenomenon, the cause of flow loss, is similar to the flow behind a blunt body. As NPR increases the location of Mach disk, characteristics of the normal shock, moves downstream and its strength increases. The Mach number distribution appears in a wave-type patter after the normal shock because oblique shocks are reflected on the shock boundaries especially when NPRs are very high.

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Effects of Slot Configurations on the Passive Control of Oblique-Shock-Interaction Flows (슬롯 형상이 경사충격파 간섭유동의 피동제어에 미치는 영향에 관한 연구)

  • Jang, Seong-Ha;Lee, Yeol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.12
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    • pp.18-24
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    • 2006
  • Passive control of the shock wave/turbulent boundary-layer interaction utilizing slotted plates and a porous plate over a cavity has been carried out. Effect of various slot configurations on the characteristics of the interaction has been observed. Pitot/wall surface pressure distributions and flow visualizations including Schlieren images, kerosene-lampblack tracings and interference fringe patterns over a thin oil-film have been obtained at the downstream of the shock interactions. For the streamwise-slot configuration, a local higher pitot pressure was noticed at the downstream of the interaction as compared with the case of no control, however, not much improvement in pitot pressure was observed for the spanwise-slot configuration.

A Study of the Influence of the Injection Location of Supersonic Sweeping Jet for the Control of Shock-Induced Separation (경사충격파 박리유동 제어를 위한 초음속 진동제트 분출위치의 영향성 연구)

  • Park, Sang-Hoon;Lee, Yeol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.50 no.11
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    • pp.747-754
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    • 2022
  • An experimental study was carried out to control a shock-induced boundary layer separation by utilizing the supersonic sweeping jet from the fluidic oscillator. High-speed schlieren, surface flow visualization, wall pressure measurement and precise Pitot tube measurement were applied to observe the influences of the location and the supply pressure of the fluidic oscillator on the characteristics of the oblique-shock-induced boundary layer separation. The characteristics of the separation control by the present supersonic fluidic oscillator was quantitatively analyzed by comparing with a conventional control method utilizing an air-jet vortex generator.

Electron Firehose Instabilities in High-β Intracluster Medium

  • Kim, Sunjung;Ha, Ji-Hoon;Ryu, Dongsu;Kang, Hyesung
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.2
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    • pp.55.2-55.2
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    • 2019
  • The firehose instability is driven by a pressure anisotropy in a magnetized plasma when the temperature along the magnetic field is higher than the perpendicular temperature. Such condition occurs commonly in astrophysical and space environments, for instance, when there are beams aligned with the background magnetic field. Recently, it was argued that, in weak quasi-perpendicular shocks in the high-β intracluster medium (ICM), shock-reflected electrons propagating upstream cause the temperature anisotropy. This electron temperature anisotropy can trigger the electron firehose instability (EFI), which excites oblique waves in the shock foot. Scattering of electrons by these waves enables multiple cycles of shock drift acceleration (SDA) in the preshock region, leading to the electron injection to diffusive shock acceleration (DSA). In the study, the kinetic properties of the EFI are examined by the linear stability analysis based on the kinetic Vlasov-Maxwell theory and then further investigated by 2D Particle-in-Cell (PIC) simulations, especially focusing on those in high-β (β~100) plasmas. We then discuss the basic properties of the firehose instability, and the implication of our work on electron acceleration in ICM shock.

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Influence of a isolator in supersonic nozzle on thermal choking (초음속 노즐의 분리부가 열폐색에 미치는 영향)

  • Kim, Sangwoo;Kim, Youngcheol;Kim, Jangwoo
    • 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.

A Study on the Aerodynamic Noise of a Supersonic Exhaust Nozzle of Slotted Tube (슬롯관형 초음속 배기노즐의 공력소음에 관한 연구)

  • Lee, Dong-Hoon;Seto, Kunisato
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.1
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    • pp.132-142
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    • 2000
  • The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

Assessment of dynamic crushing and energy absorption characteristics of thin-walled cylinders due to axial and oblique impact load

  • Baaskaran, N.;Ponappa, K.;Shankar, S.
    • Steel and Composite Structures
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    • v.28 no.2
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    • pp.179-194
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    • 2018
  • Reliable and accurate method of computationally aided design processes of advanced thin walled structures in automotive industries are much essential for the efficient usage of smart materials, that possess higher energy absorption in dynamic compression loading. In this paper, most versatile components i.e., thin walled crash tubes with different geometrical profiles are introduced in view of mitigating the impact of varying cross section in crash behavior and energy absorption characteristics. Apart from the geometrical parameters such as length, diameter and thickness, the non-dimensionalized parameters of average forces which control the plastic bending moment for varying thickness has explored in view of quantifying its impact on the crashworthiness of the structure. The explicit finite element code ABAQUS is utilized to conduct the numerical studies to examine the effect of parametric modifications in crash behavior and energy absorption. Also the simulation results are experimentally validated. It is evident that the circular cross-sectional tubes are preferable as high collision impact shock absorbers due to their ability in withstanding axial and oblique impact loads effectively. Furthermore, the specific energy absorption (SEA), crash force efficiency (CFE), plastic bending moment, peak force responses and its impact for optimally tailoring a design to cater the crashworthiness requirements are investigated. The primary outcome of the study is to provide sufficient information on circular tubes for the use of energy absorbers where impact oblique loading is expected.

Flow Analysis of POSRV Subsystem of Standard Korean Nuclear Reactor (한국 표준형 원전의 POSRV 하부 배관 유동해석)

  • Kwon, Soon-Bum;Kim, In-Goo;Ahn, Hyung-Joon;Lee, Dong-Eum;Baek, Seung-Cheol;Lee, Byeong-Eun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.27 no.10
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    • pp.1464-1471
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    • 2003
  • In order to investigate the flows with shock wave in branch, 108$^{\circ}$ elbow and T-junction of the IRWST system of standard Korean nuclear reactor, detail time dependent behaviors of unsteady flow with shock wave, vortex and so on are obtained by numerical method using compressible three-dimensional Navier-Stokes equations. At first, the complex flow including the incident and reflected shock waves, vortex and expansion waves which are generated at the corner of T-junction is calculated by the commercial code of FLUENT6 and is compared with the experimental result to obtain the validation of numerical method. Then the flow fields in above mentioned units are analyzed by numerical method of [mite volume method. In numerical analysis, the distributions of flow properties with the moving of shock wave and the forces acting on the wall of each unit which can be used to calculate the size of supporting structure in future are calculated specially. It is found that the initial shock wave of normal type is re-established its type from an oblique one having the same strength of the initial shock wave at the 4 times hydraulic diameters of downstream from the branch point of each unit. Finally, it is turned out that the maximum force acting on the pipe wall becomes in order of the T-junction, 108$^{\circ}$ elbow and branch in magnitude, respectively.

ACCURACY IMPROVEMENT OF THE BLEED BOUNDARY CONDITION WITH THE EFFECTS OF POROSITY VARIATIONS AND EXPANSION WAVES (다공도 및 팽창파의 영향을 고려한 BLEED 경계조건 수치 모델링의 정확도 향상 연구)

  • Kim, G.;Choe, Y.;Kim, C.
    • Journal of computational fluids engineering
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    • v.21 no.1
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    • pp.94-102
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    • 2016
  • The present paper deals with accuracy improvement of a bleed boundary condition model used to improve the performance of supersonic inlets. In order to accurately predict the amount of bleed mass flow rates, this study performs a scaling of sonic flow coefficient data for 90-degree bleed holes in consideration of Prandtl-Meyer expansion theory. Furthermore, it is assumed that porosity varies with stream-wise location of the porous bleed plate to accurately predict downstream boundary layer profiles. The bleed boundary condition model is demonstrated through Computational Fluid Dynamics(CFD) simulations of bleed flows on a flat plate with/without an oblique shock. As a result, the bleed model shows the improved accuracy of bleed mass rates and downstream boundary layer profiles.