• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.11 no.9
• /
• pp.406-413
• /
• 2001

The current study depicts and experimental work of the impulsive wave discharged from the exit of several kinds of right-angle bend pipes, which are attached to the open end of a simple shock tube. The weak normal shock wave with Mach number from 1.02 to 1.20 is employed to obtain the impulsive wave propagating outside the exit of the pipe bends. The experimental data of the magnitude of the impulsive wave and its propagation directivity are analyzed to characterize the impulsive waves discharged from the right-angle bend pipes and compared with those from a straight pipe. The impulsive waves are visualized by a Schlieren optical system. A computation work using the two-dimensional, unsteady, compressible Euler equation is also carried out to represent the experimented impulsive waves. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulsive wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right angle miter bend pipe can play a role of passive control agianst the impulsive wave.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.48 no.11
• /
• pp.849-859
• /
• 2020

The semi-empirical equation and commercial computational tool were used to predict the base drag of a guided missile with free-stream Mach numbers and chamber pressures, and the results were generally agree each other. Differences in flow characteristics and base drags were observed with over/under expansion conditions by the nozzle. Under the over-expansion condition, the base pressure decreased as the expansion fan was generated at upper region of the base, and base pressure decreased further with increasing free-stream Mach number as the expansion becomes strong. Under the under-expansion conditions, a shock wave was generated around the base by the influence of the nozzle flow, which increased the base pressure, and the effect increased as the chamber pressure increased. Under the same chamber pressure condition, as the free-stream Mach number increases, the characteristic that the base pressure decreases as the shock wave generated at the base moves downstream was observed.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.2066-2070
• /
• 2003

This experimental study describes the propagation characteristics and suppression of the impulse noise emitted from the exit of a perforated pipe attached to the open end of a simple shock tube. The experiment is performed through the systematic change of the shock wave Mach number and the geometrical parameters such as the porosity, hole diameter and length of the perforated pipe. The experimental results for the near and far sound field are presented and explained in comparison with those for a straight pipe. The results obtained show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the all directions, indicating that the directivity pattern is almost same regardless of the pipe type. Moreover, the noise reduction performance of perforated pipe depends upon the condition of sound field. For the near sound field the perforated pipe has a little performance to suppress the impulse noise, but for the far sound field the perforated pipe has little performance to suppress the impulse noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.168-173
• /
• 2003

This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a perforated pipe attached to the open end of a simple shock tube. The pressure amplitudes and directivities of the impulse wave propagating from the exit of perforated pipe with several different configurations are measured and analyzed fur the range of the incident shock wave Mach number between 1.02 and 1.2. In the experiments, the impulse waves are visualized by a Schlieren optical system for the purpose of investigating their propagation pattern. The results obtained show that for the near sound field the impulse noise strongly propagates toward to the pipe axis, but for the far sound field the impulse noise uniformly propagates toward to the all directions, indicating that the directivity pattern is almost same regardless of the pipe type. Moreover, it is shown that for the far sound field the perforated pipe has little performance to suppress the impulse noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• 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.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.187-188
• /
• 2004

압전식 충격파 쇄석기를 사용하여 대상물을 파쇄하는 과정에서 발생하는 음의 특성을 조사한 결과, 대상물이 파쇄됨에 따라 방사음이 더욱 저주파대로 이동한다는 사실을 알았다. 이 사실을 입증하기 위하여 대상물의 파쇄상태를 모델링한 대상물을 사용한 실험에서는 동일한 결과를 관측할 수 있었다. 따라서, 본 논문에서는 실험적으로 추정된 연구결과를 이론적으로 확인하기 위하여 유한요소법을 이용한 수치 시뮬레이션을 실험과 유사하게 모델링한 대상물에 실행하였고, 시뮬레이션에서 관측된 결과를 제시하여 대상 연구결과의 유효성을 입증하였다.

• Journal of KSNVE
• /
• v.11 no.2
• /
• pp.241-248
• /
• 2001

The present paper describes experimental and computational work to augment the magnitude of the impulsive wave. An experiment was performed using a simple shock tube with an open end and numerical calculations were carried out to solve the unsteady, axisymmetric, inviscid, compressible governing equations. The control strategy applied was to alter the exit geometry of a straight tube to a sudden enlargement tube and a flare tube. The effects of the configurations of the tube exit on the magnitude of the impulsive wave were investigated over the range of the weak shock Mach number from 1.01 to 1.10. The results obtained were compared to those of the straight tube tests. The numerical result predicted the magnitude of the experimented impulsive waves with a good accuracy. The present passive control technique enabled the magnitude of the impulsive wave to augment by about 23 percent, compared to that of the straight tube of no control.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.371-375
• /
• 2006

A computational work has been performed to investigate the aerodynamics of a projectile which is launched from a ballistic range. A moving coordinate method for a multi-domain technique is employed to simulate unsteady projectile flows with a moving boundary. The variation of a virtual mass and the shape of projectile are added to the axisymmetric unsteady Euler equation systems. The present computational results properly predict the velocity, acceleration, drag histories and the major flow characteristics of the projectile.

• Journal of Energy Engineering
• /
• v.21 no.3
• /
• pp.237-242
• /
• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.12 no.5
• /
• pp.346-354
• /
• 2002

The present study is to investigate the propagation characteristics of the impulse waves discharged from the exit of the convergent and divergent pipes. An experiment is carried out using a shock tube with an open end and is compared to the computation of the axisymmetric, compressible, unsteady Euler equations, which are solved by the second-order total variation diminishing (TVD) scheme. For the computational work, several initial compression waves are assumed inside the pipe so that those are the same to the experimental ones of the shock tube. The results show that the peak pressures of the impulse waves discharged from the exit of convergent and divergent pipes decrease with an increase in the wavelength of the initial compression wave. All of the impulse waves have a strong directivity toward the pipe axis, regardless of the exit type of the pipe employed. The impulse waves discharged from the divergent pipe are stronger than those from the straight pipe, while the impulse waves of the convergent pipe are weaker than those from the straight pipe. It is found that the convergent pipe can play a role of a passive control to reduce the peak pressure of the impulse wave. The present computations represent the experimented impulse waves with a good accuracy.