• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.1742-1747
• /
• 2003

When a shock wave is discharged from the exit of a duct, complicated flow is formed near the duct exit. The flow field is much more complicated under the ground effects or any other objects near the exit of a duct, such as the circumstance near the exit of the high-speed railway tunnel. The resulting flow is essentially three-dimensional unsteady with the effects of strong compressibility. In the current study, three-dimensional flow fields of the weak shock wave which is discharged from the exit of a duct are numerically investigated using a CFD method. Computations are performed for the weak shock wave in the range below 1.5. The results obtained show that the directivity and magnitude of the weak shock discharged strongly depend upon the Mach number of initial shock wave and are significantly influenced by the ground effects.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 춘계학술대회논문집
• /
• pp.852-855
• /
• 2004

This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a straight pipe attached to the open end of a simple shock tube. The sound pressure level and directivity of the impulse noise propagating from the exit of pipe with several different diameters are measured in the far sound fold for the range of the incident shock wave Mach number between 1.07 and 1.26. The experimental results showed that the peak values of impulse noises had a strong dependance on the exit diameter of a pipe and the shock wave Mach number. The impulse noise had the directivity propagating toward to the pipe axis and the characteristics of inverse square law of propagation distance. Moreover, it was shown that the one-third octave band SPL of impulse noise was almost constant regardless of the frequency band.

• 대한기계학회논문집B
• /
• 제26권9호
• /
• pp.1311-1318
• /
• 2002

An experimental model is investigated in this paper using the experimental method with a shock tube and the numerical technique. The shock-vortex interaction generated by this model is visualized with various methods: holographic interferometry, shodowgraphy, and numerical computation. In terms of shock dynamics, there are two meaningful physics in the present problem. They are reflective wave from the slip layer at the vortex edge and transmitted shock penetrating the vortex core. The discussion in this study is mainly focused on the two kinds of waves contributing to the quadrupolar pressure distribution around the vortex center during the interaction.

• 소음진동
• /
• 제11권2호
• /
• pp.285-291
• /
• 2001

The impingement of a weak shock wane discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was varied in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• 대한기계학회논문집
• /
• 제19권5호
• /
• pp.1280-1290
• /
• 1995

In order to investigate the compression wave propagating in a high-speed railway tunnel, a numerical calculation was applied to the wave phenomenon occurring in a model tunnel. Unsteady, one-dimensional inviscid or viscous flows were solved by an explicit TVD scheme, and the calculated flows were compared with the results of measurement in real tunnels. Tunnel noises caused by emission of the compression wave were characterized in terms of excess pressure of compression wave, pressure gradient in the wave front and width of the compression wave. Calculated attenuation, pressure gradient and width of compression wave with the propagating distance agreed with the results of measurement in the real tunnels. The results also show that tunnel noises are proportional to the train velocity entering the tunnel.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.462-467
• /
• 2001

The present study addresses a computational work of the weak shock wave propagatings inside a silencer system of automobile exhaust pipe. Four different types of the silencer systems and the initial shock wave Mach number $M_s$ of $1.01\sim1.30$ are applied to investigate their effects on the noise reduction and the flow field in a silencer system. The results obtained from the present computational work are compared with the experimental results. The second order total variation diminishing (TVD) scheme is employed to solve the two dimensional, compressible, unsteady, Euler equations. The present computational results predict the experimental results with a quite good accuracy. Of the four silencer systems applied, the most desirable silencer system to reduce the peak pressure at the exit of the exhaust pipe is discussed.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.792-797
• /
• 2003

A helical vane is applied to reduce the magnitude of the impulse wave discharged from the exit of a duct. A shock tube with an open end is used to investigate the effect of the helical vanes on the impulse wave magnitude. Four different types of helical vanes are installed into the low-pressure tube of shock tube. The magnitude of the incident shock wave is varied below 1.25, and the magnitude of impulse wave is measured using a pressure transducer mounted on a wedge probe. Instant images of the impulse wave are obtained by means of the Schlieren optical method. The present experimental results show that the helical vane considerably reduces the magnitude of the impulse wave and the vane effects are more remarkable for stronger incident shock wave.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.544-549
• /
• 2003

When a shock wave arrives at an open end of tube, an impulse wave is discharged from the tube exit and causes serious noise and vibration problems. In the current study, the effect of the cross-sectional area of tube on the impulse wave is numerically investigated using a CFD method. The Harten-Yee's total variation diminishing(TVD) scheme is used to solve the axisymmetric, two-dimensional, unsteady, compressible Euler equations. With three different cross-sectional areas of tube, the Mach number of the incident shock wave $M_{s}$ is varied between 1.01 and 1.5. The results obtained show that the directivity and magnitude of impulse wave strongly depend upon the Mach number of incident shock wave and are influenced by the tube area. It is also known that the tube cross-sectional area significantly affects the magnitude of impulse wave at or near the tube axis.

• 대한기계학회논문집B
• /
• 제23권7호
• /
• pp.901-910
• /
• 1999

Investigated In this paper is the shock reflection from a blunt body, In particular, a circular cylinder of 20 mm diameter, for the weak shock impinging in the range 1<$M_s$ <2. Pressure and shock speed are measured for various shock strengths. Double-pulse holographic interferograms are taken to study the unsteady flow field at $M_s=1.34$. These experimental results are, in overall, well compared with the unstructured adaptive finite volume computation of the Euler equations performed in this study. Correlation of incident and reflected shocks and shock-shock locus obtained by experiment, computation, and theory are presented in parallel.

• 대한기계학회논문집B
• /
• 제21권10호
• /
• pp.1294-1302
• /
• 1997

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.