• Title/Summary/Keyword: Shock tunnel

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Passive control of condensation shock wave in supersonic nozzles (초음속 노즐에서 발생하는 응축충격파의 피동제어)

  • Kim, Hui-Dong;Gwon, Sun-Beom;Setoguchi, Toshiaki
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.12
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    • pp.3980-3990
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    • 1996
  • When a moist air is rapidly expanded in a supersonic nozzle, nonequilibrium condensation occurs at a supersaturation state. Condensation shock wave appears in the nozzle flow if the releasing latent heat due to condensation goes beyond a critical value. It has been known that self-excited oscillations of the condensation shock wave generate in an air or a steam nozzle flow with a large humidity. In the present study, the passive control technique using porous wall with a cavity underneath was applied to the condensation shock wave. The effects of the passive control on the steady and self-excited condensation shock waves were experimentally investigated by Schlieren visualization and static pressure measurements. The result shows that the present passive control is a useful technique to suppress the self-excited oscillations of condensation shock wave.

Effects of supersonic condensing nozzle flow on oblique shock wave (超音速 노즐흐름에 있어서 凝縮이 傾斜衝擊波에 미치는 影響)

  • 강창수;권순범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.3
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    • pp.547-553
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    • 1989
  • Last several stages of high capacity fossil power steam turbine and most stages of nuclear power steam turbine operate on wet steam. As a consequence, the flows in those cascades are accompanied by condensation, and the latent heat caused by condensation affects an oblique shock wave being generated at the vicinity of trailing of the blade. In the case of expanding of moist air through a suction type indraft wind tunnel, the effect of condensation affection the oblique shock wave generated by placing the small wedge into the supersonic part of the nozzle was investigated experimentally. In these connections, the relationship between condensation zone and reflection point of the incident oblique shock wave, angle between wedge bottom wall and oblique shock wave, and the variations of angles of incident and reflected shock waves due to the variation of initial stagnation relative humidity are discussed. Furthermore, the relationship between initial stagnation relative humidity and load working on the nozzle wall, obtained by measuring static pressure at the nozzle centerline, is discussed.

Aerodynamic Analysis of a Train Running in a Tunnel(II)-Aerodynamics of Two-Trains- (터널내를 주행하는 열차의 공기역학적 해석(II)-2열차의 공기역학-)

  • Kim, Hui-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.8
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    • pp.983-995
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    • 1997
  • As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect backward at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves can give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfort for the passengers in the train. In the present study, the pressure transients and aerodynamic drag for two-trains running in a tunnel were calculated numerically for a wide range of train speed, and compared with the results of the previous tunnel tests and calculations for one train. The present calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.

Numerical study on attenuation and distortion of compression wave propagation into a straight tube (직관내를 전파하는 압축파의 감쇠와 변형에 관한 수치해석적 연구)

  • Kim, Hui-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.7
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    • pp.2315-2325
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    • 1996
  • A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

Numerical Study of Thermal Choking Process in a Model SCRamjet Combustor (모델 스크램제트 연소기 내의 열적 질식 과정 수치 연구)

  • Lee, B.R.;Moon, G.W.;Jeung, I.S.;Choi, J.Y.
    • 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.

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A Study on the installation time and method of soundproofing facilities according to a Tunnel blasting work. (터널발파작업에 따른 방음시설의 설치시기와 방법에 대한 고찰.)

  • Won, Yeon-Ho;Son, Young-Bok;Jeong, Jai-Hyung
    • Proceedings of the KSEE Conference
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    • 2006.10a
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    • pp.119-140
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    • 2006
  • The rock excavation work by doing blasting breaks the rock by using a shock pressure and gas pressure produced when explosive explodes and the shock wave by shock pressure propagated three-dimensionally from the exploding center is on the decrease notably to the distance, however, $0.5{\sim}20%$ of energy produced by blasting propagates into the ground outside a crack zone by the shape of an elastic wave, on the ground it appears as a ground vibration with a seismic amplitude and a seismic cycle, it is called a blasting vibration. on the other side, what propagated in the air is called a blasting sound. The blasting sound of both means the things which the shock sound within the range the audible frequency($20{\sim}20000Hz$) of the elastic wave in the air influences the response system of a human body, it doesn't harm physically to any structures but influences unreasonably a work accomplishment, such as a work discontinuance due to the outbreak of a public complaint by a mental pain, reduction of a blasting scale, etc.. So, this study is examined at about 20 sites on the installation time and method of soundproofing facilities for reduction of the sound accompanied with a tunnel blasting work.

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Aerodynamic Analysis of a Train Running in a Tunnel(I)-Aerodynamics of One-Train- (터널내를 주행하는 열차의 공기역학적 해석(I)-1열차의 공기 역학-)

  • Kim, Hui-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.8
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    • pp.963-972
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    • 1997
  • As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfortableness of the passengers in the train. In the present study, the pressure transients were calculated numerically for a wide range of train speed and compared with the previous tunnel tests. The calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.

Passive control of strength of shock wave (다공벽을 이용한 충격파 강도의 피동제어)

  • Choe, Yeong-Sang;Gwon, Sun-Beom;Jo, Cheol-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.1
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    • pp.174-184
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    • 1997
  • A shock wave, being an irreversible process, gives rise to entropy increase. A great deal of effort has been made to control shock wave and boundary layer interaction related to energy losses as well as problems of vibration and noise. In the present study, tests are performed on a roof mounted half circular arc in an indraft type supersonic wind tunnel to evaluate the effects of porosity, length and depth of cavity in passive control of shock wave on the attenuation of shock strength by reviewing the measured static pressures at the porous wall and cavity. Also the flow field is visualized by a Schlieren system. The results show that in the present study the porosity of 8% produced the largest reduction of pressure fluctuations and that for the same porosity, the strength of shock wave decreases with the increasings of the depth and length of cavity.

Passive Control of the Condensation Shock Wave Oscillation in a Supersonic Nozzle (초음속 노즐에서 발생하는 응축충격파 진동의 피동제어)

  • Baek, Seung-Cheol;Kwon, Soon-Bum;Kim, Heuy-Dong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.7
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    • pp.951-958
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    • 2002
  • Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

Computations on Passive Control of Normal Shock-Wave/Turbulent Boundary-Layer Interactions (수직충격파와 난류경계층의 간섭유동의 피동제어에 관한 수치 해석)

  • 구병수;김희동
    • Journal of the Korean Society of Propulsion Engineers
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    • v.5 no.3
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    • pp.25-32
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    • 2001
  • A passive control method of the interaction between a weak normal shock-wave and a turbulent boundary-layer was simulated using two-dimensional Navier-Stokes computations. The inflow Mach number just upstream of the normal shock wave was 1.33. A porous plate wall having a cavity underneath was used to control the shock-wave/turbulent boundary-layer interaction. The flows through the porous holes and inside the cavity were investigated to get a better understanding of the flow physics involved in this kind of passive control method. The present computations were validated by some recent wind tunnel tests. The results showed that downstream of the rear leg of the $\lambda$-shock wave the main stream inflows into the cavity, but upstream of the rear leg of the $\lambda$-shock wave the flow proceeds from the cavity toward to the main stream. The flow through the porous holes did not choke fur the present shock/boundary layer interaction.

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