• Title, Summary, Keyword: Shock Wave

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Shock-Wave Oscillation in a Supersonic Diffuser -Displacement Measurement of Mormal Shock-Wave- (초음속 디퓨져에서 충격파의 진동 (1) -수직충격파의 순간변위 측정-)

  • 김희동;엄용균;권순범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.4
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    • pp.933-945
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    • 1994
  • A shock-wave in a supersonic flow can be theoretically determined by a given pressure ratio at upstream and downstream flowfields, and then the obtained shock-wave is stable in its position. Under the practical situation in which the shock-wave interacts with the boundary layer along a solid wall, it cannot, however, be stable even for the given pressure ratio being independent of time and oscillates around a time-mean position. In the present study, oscillations of a weak normal shock-wave in a supersonic diffuser were measured by a Line Image Sensor(LIS), and they were compared with the data of the wall pressure fluctuations at the foot of the shock-wave interacting with the wall boundary layer. LIS was incorporated into a conventional schlieren optical system and its signal, instantaneous displacement of the interacting shock-wave, was analyzed by a statistical method. The results show that the displacement of an oscillating shock-wave increase with the upstream Mach number and the dominant frequency components of the oscillating shock-wave are below 200 Hz. Measurements indicated that shock-wave oscillations may not entirely be caused by the boundary layer separation. The statistical properties of oscillations appeared, however, to be significantly affected by shock-induced separation of turbulent boundary layer.

Geometrical characterization of the cavitation bubble clouds produced by a clinical shock wave device

  • Choi, Min Joo;Kang, Gwansuk;Huh, Jung Sik
    • Biomedical Engineering Letters
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    • v.7 no.2
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    • pp.143-151
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    • 2017
  • This study was to optically visualize the cavitation bubbles produced by a clinical shock wave and to look into their geometric features of the resulting cavitation bubbles in relation to the driving shock wave field. A clinical shock wave therapeutic system was taken for shock wave production. The shock wave induced cavitation bubbles were captured by a professional camera under the illumination of a micro-pulse LED light. The light exposure was set to last for the whole life time of bubbles from formation to subsequent collapses. It was shown that the cavitation bubbles appeared mostly in the vicinity of the focus. The bubbles became more and larger as approaching to the focus. The cavitation bubbles formed jet streams which became enlarged (stronger) as the shock wave device output setting increased. The bubble cloud boundary was reasonably fitted to an elongated ellipsoid characteristically similar to the acoustic focal area. The bubble clouds were enlarged as the output setting increased. The geometric features of the cavitation bubbles characteristically similar to those of the focusing acoustic field have potential to provide the therapeutic focal information without time consuming hydrophone measurements of the shock wave field causing damages of the expensive sensor. The present study is limited to the static afterimages of the cavitation bubbles and investigation including the bubble dynamics is suggested to deliver the more realistic therapeutic area of the shock wave therapy.

Experimental Study Shock Waves in Superfluid Helium Induced by a Gasdynamic Shock Wave Impingement

  • Yang, Hyung-Suk;Nagai, Hiroki;Murakami, Masahide;Ueta, Yasuhiro
    • Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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    • pp.43-47
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    • 2000
  • Two modes of shock waves, a compression shock wave and a thermal shock wave, propagating in He II have been investigated. The shock waves are at a time generated by the impingement of a gasdynamic shock wave onto a He II free surface in the newly developed superfluid shock tube facility. Superconductive temperature sensors, piezo-type pressure transducers and visualization photograph were used for the measurement of them and the phenomena induced by them were investigated in detail. It is found that the compression by a compression shock wave in He II causes temperature drop because He II has negative thermal expansion coefficient. the thermal shock wave is found to be of a single triangular waveform with a limited shock strength. The waveform is similar to that generated by stepwise strong heating from an electrical heater for relatively long heating time. In the experiments at the temperatures near the lambda temperature, no thermal shock wave is sometimes detected in shock compressed He II. It can be understood that shock compression makes He Ii convert to He I in which no thermal shock wave is excited.

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Numerical Visualization of the Unsteady Shock Wave Flow Field in Micro Shock Tube

  • Arun, Kumar R.;Kim, Heuy-Dong
    • Journal of the Korean Society of Visualization
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    • v.10 no.1
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    • pp.40-46
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    • 2012
  • Recently micro shock tube is extensively being used in many diverse fields of engineering applications but the detailed flow physics involved in it is hardly known due to high Knudsen number and strong compressibility effects. Unlike the macro shock tube, the surface area to volume ratio for a micro shock tube is very large. This unique effect brings many complexities into the flow physics that makes the micro shock tube different compared with the macro shock tube. In micro shock tube, the inter- molecular forces of working gas can play an important role in specifying the flow characteristics of the unsteady shock wave flow which is essentially generated in all kinds of shock tubes. In the present study, a CFD method was used to predict and visualize the unsteady shock wave flows using the unsteady compressible Navier-Stokes equations, furnished with the no-slip and slip wall boundary conditions. Maxwell's slip equations were used to mathematically model the shock movement at high Knudsen number. The present CFD results show that the propagation speed of the shock wave is directly proportional to the initial pressure and diameter of micro shock tube.

A Computational Study of the Focusing Phenomenon of Weak Shock Wave (약한 충격파의 포커싱 현상에 관한 수치해석적 연구)

  • Kweon Yong Hun;Kim Heuy Dong
    • Proceedings of the KSME Conference
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    • pp.169-172
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    • 2002
  • When a plane shockwave reflects ken a concave wall, it is focused at a certain location, resulting in extremely high local pressure and temperature. This focusing is due to a nonlinear phenomenon of shock wave. The focusing phenomenon has been extensively applied to many diverse folds of engineering and medical treatment as well. In the current study, the focusing of shock wave over a reflector is numerically investigated using a CFD method. The Harten-Yee total variation diminishing (TVD) scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The incident shock wave Mach number $M_{s}\;of\;1.1{\~}l.3$ is applied to the parabolic reflectors with several different depths. Detailed focusing characteristics of the shock wave are investigated in terms of peak pressure, gasdynamic and geometrical foci. The results obtained are compared with the previous experimental results. The results obtained show that the peak pressure of shock wave focusing and its location strongly depend on the magnitude of the incident shock wave and depth of parabolic reflector. It is also found that depending up on the depth of parabolic reflector, the weak shock wave focusing process can classified into three distinct patterns : the reflected shock waves do not intersect each other before and after focusing, the reflected shock waves do not intersect each other before focusing, but intersect after focusing, and the reflected shock waves intersect each other before and after focusing. The predicted Schlieren images represent the measured shock wave focusing with a good accuracy.

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Numerical Simulations of an Unsteady Shock Wave Propagating into a Helmholtz Resonator (Helmholtz 공명기 내부를 전파하는 비정상 충격파의 수치해석)

  • Lee, Y.K.;Gweon, Y.H.;Shin, H.D.;Kim, H.D.;AOKI, T.
    • Proceedings of the KSME Conference
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    • pp.1643-1648
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    • 2004
  • When a shock wave propagates into a Helmholtz resonator, very complicated wave phenomena are formed both inside and outside the resonator tube. Shock wave reflection, shock focusing phenomena and shock-vortex interactions cause strong pressure fluctuations inside the resonator, consequently leading to powerful sound emission. In the present study, the wave phenomena inside and outside the Helmholtz resonator are, in detail, investigated with a help of CFD. The Mach number of the incident shock wave is varied below 2.0 and several types of resonators are tested to investigate the influence of resonator geometry on the wave phenomena. A TVD scheme is employed to solve the axisymmetric, compressible, Euler equations. The results obtained show that the configuration of the Helmholtz resonator significantly affects the peak pressure of shock wave focusing, its location, the amplitude of the discharged wave and resonance frequency.

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THE FUNDAMENTAL SHOCK-VORTEX INTERACTION PATTERNS THAT DEPEND ON THE VORTEX FLOW REGIMES

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • Journal of computational fluids engineering
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    • v.14 no.3
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    • pp.76-85
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    • 2009
  • The shock wave is deformed and the vortex is elongated simultaneously during the shock-vortex interaction. More precisely, the shock wave is deformed to a S-shape, consisting of a leading shock and a lagging shock by which the corresponding local vortex flows are accelerated and decelerated, respectively: the vortex flow swept by the leading shock is locally expanded and the one behind the lagging shock is locally compressed. As the leading shock escapes the vortex in the order of microseconds, the expanded flow region is quickly changed to a compression region due to the implosion effect. An induced shock is developed here and propagated against the vortex flow. This happens for a strong vortex because the tangential flow velocity of the vortex core is high enough to make the induced-shock wave speed supersonic relative to the vortex flow. For a weak shock, the vortex is basically subsonic and the induced shock wave is absent. For a vortex of intermediate strength, an induced shock wave is developed in the supersonic region but dissipated prematurely in the subsonic region. We have expounded these three shock-vortex interaction patterns that depend on the vortex flow regime using a third-order ENO method and numerical shadowgraphs.

Aerodynamic control capability of a wing-flap in hypersonic, rarefied regime

  • Zuppardi, Gennaro
    • Advances in aircraft and spacecraft science
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    • v.2 no.1
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    • pp.45-56
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    • 2015
  • The attitude aerodynamic control is an important subject in the design of an aerospace plane. Usually, at high altitudes, this control is fulfilled by thrusters so that the implementation of an aerodynamic control of the vehicle has the advantage of reducing the amount of thrusters fuel to be loaded on board. In the present paper, the efficiency of a wing-flap has been evaluated considering a NACA 0010 airfoil with a trailing edge flap of length equal to 35% of the chord. Computational tests have been carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km, in the range of angle of attack 0-40 deg. and with flap deflection equal to 0, 15 and 30 deg.. Effects of the flap deflection have been quantified by the variations of the aerodynamic force and of the longitudinal moment. The shock wave-boundary layer interaction and the shock wave-shock wave interaction have been also considered. A possible interaction of the leading edge shock wave and of the shock wave arising from the vertex of the convex corner, produced on the lower surface of the airfoil when the flap is deflected, generates a shock wave whose intensity is stronger than those of the two interacting shock waves. This produces a consistent increment of pressure and heat flux on the lower surface of the flap, where a thermal protection system is required.

Experimental analysis of flow field for laser shock wave cleaning (레이저 충격파 클리닝에서 발생되는 유동장의 실험적 해석)

  • 임현규;장덕석;김동식
    • Laser Solutions
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    • v.7 no.1
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    • pp.29-36
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    • 2004
  • The dynamics of laser-induced plasma/shock wave and the interaction with a surface in the laser shock cleaning process are analyzed by optical diagnostics. Shock wave is generated by a Q-switched Nd:YAG laser in air or with N$_2$, Ar, and He injection into the focal spot. The shock speed is measured by monitoring the photoacoustic probe-beam deflection signal under different conditions. In addition, nanosecond time-resolved images of shock wave propagation and interaction with the substrate are obtained by the laser-flash shadowgraphy. The results reveal the effect of various operation parameters of the laser shock cleaning process on shock wave intensity, energy-conversion efficiency, and flow characteristics. Discussions are made on the cleaning mechanisms based on the experimental observations.

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Reduction of Normal Shock-Wave Oscillations by Turbulent Boundary Layer Flow Suction (경계층 유동의 흡입에 의한 수직충격파 진동저감)

  • Kim, Heuy Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.9
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    • pp.1229-1237
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    • 1998
  • Experiments of shock-wave/turbulent boundary layer interaction were conducted by using a supersonic wind tunnel. Nominal Mach number was varied in the range of 1.6 to 3.0 by means of different nozzles. The objective of the present study is to investigate the effects of boundary layer suction on normal shock-wave oscillations caused by shock wave/boundary layer interaction in a straight duct. Two-dimensional slits were installed on the top and bottom walls of the duct to bleed turbulent boundary layer flows. The bleed flows were measured by an orifice. The ratio of the bleed mass flow to main mass flow was controlled below the range of 11 per cent. Time-mean and fluctuating wall pressures were measured, and Schlieren optical observations were made to investigate time-mean flow field. Time variations in the shock wave displacement were obtained by a high-speed camera system. The results show that boundary layer suction by slits considerably reduce shock-wave oscillations. For the design Mach number of 2.3, the maximum amplitude of the oscillating shock-wave reduces by about 75% compared with the case of no slit for boundary layer suction.