• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2000.11a
• /
• pp.36-36
• /
• 2000

천음속 또는 초음속 유동이 유동장의 하류에서 부여되는 압력조건에 의하여 감속되는 경우나, 유동방향의 갑작스런 변화를 요구하는 물체 혹은 벽면이 존재하는 경우에 발생한 충격파는 벽면을 따라 발생하는 층류 혹은 난류 경계층과 복잡한 상호간섭 (interaction)을 일으켜 충격파에 의한 박리 발생, 충격파 하류에 새로운 충격파 발생, 충격파가 큰 진폭으로 진동하게 되는 현상 등을 발생시킨다. 이러한 간섭현상은 고속유동이 통과하는 유체요소나 유체기기의 성능을 좌우하는 매우 중요한 유동현상으로, 유체기계의 설계 시 사전에 고려되어야 할 중요한 공학적 문제이다.(중략)

• Proceeding of EDISON Challenge
• /
• 2016.11a
• /
• pp.96-100
• /
• 2016

슬롯판을 이용한 경사충격파와 경계층 간섭유동 제어에서, 슬롯의 각도를 바꾸어 가며 제어 성능을 비교하는 수치적 연구가 수행되었다. 기준이 되는 수직 슬롯, 각도를 달리한 6개의 case를 선정하여 하여 충격파 뒤에서 전압손실 및 경계층 안정성을 기준으로 제어 성능을 평가하였다. 수치해석 결과 모든 형상에 대해 제어하지 않은 상태보다 좋은 성능을 얻었다. 공력성능이 뛰어난 그룹과 그렇지 않은 그룹을 구분하여 슬롯과 공동 유동 구조를 분석하면서 경계층 불안정성을 야기하고 전압손실 감소에 영향을 미치는 것은 경계층과 충격파가 상호작용하는 영역에서 Vortex를 얼마나 제어할 수 있는지 여부임을 알 수 있었고, 이러한 Vortex를 얼마나 제어할 수 있는지에 따라 공력 성능이 결정됨을 파악할 수 있었다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.4
• /
• pp.33-38
• /
• 2003

The Physics of the Plume-induced shock and separation Particularly at a high Plume to exit pressure ratio and supersonic speeds up to Mach 3.0 with and without a passive control method, porous extension, were studied using computational techniques. Mass-averaged Navier-Stokes equations with the RNG $\kappa$-$\varepsilon$ turbulence model were solved using a fully implicit finite volume scheme and a 4-stage Runge-Kutta method. The control methodology for plume-afterbody interactions is to use a perforated wall attached at either the nozzle exit or the edge of the missile base. The Effect of porous wall length on plume interference is also investigated The computational results show the main effect of the porous extension on plume-afterbody interactions is to restrain the plume from strongly underexpanding during a change in flight conditions. With control, a change in porous extension length has no significant effect rut plume interference.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.5 no.3
• /
• pp.25-32
• /
• 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.

• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.604-609
• /
• 2016

슬롯판을 이용한 경사충격파와 경계층 간섭유동 제어에서, 슬롯판 아래에 있는 공동부의 형상을 바꾸어 가며 제어 성능을 비교하는 수치적 연구가 수행되었다. 공동형상 직사각형 5개, 사다리꼴 3개를 선정하여 shock 뒤에서 경계층 안정성, 전압손실을 기준으로 제어 성능을 평가하였다. 수치해석 결과 모든 형상에 대해 제어하지 않은 상태보다 좋은 성능을 얻었다. 그 중 경계층 안정성 측면에서는 형상 L과 R, 전압손실 감소 측면에서는 형상 M과 A가 효과적임을 확인하였고, 종합적으로 슬롯의 끝 면과 공동의 길이방향 끝 면이 일치하는 형상에서 상대적으로 좋은 결과를 얻음을 확인했다. 또한 슬롯과 공동 내부유동을 분석하면서 경계층 안정성과 전압손실 감소에 영향을 미치는 것은 separation 영역을 얼마 원활히 흡입하는지의 여부임을 알 수 있었고, 상류 슬롯에서 발생하는 shock에 대한 추후 해결 연구도 필요함을 알 수 있었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.05a
• /
• pp.45-48
• /
• 2003

The plume interference is a complex phenomenon, consisting of plume-induced boundary layer separation, separated shear layer, multiple shock waves, and their interactions. The base knowledge of plume interference effect on powered missiles and flight vehicles is not yet adequate to get an overall insight of the flow physics in plume-freestream flow field. Computational studies are performed to better understand the flow physics of the plume-induced shock and separation for Simple, Rounded, Porous-extension test model configurations. The present study simulates highly underexpanded exhaust plume effect on missile body at the transoni $c^ersonic speeds. In order to investigate the plume-induced separation phenomenon, Simple, Rounded and Porous-extension plate are attacked to the missile afterbody. The computational result shows that the rounded afterbody and the porous-extension wall attached at the missile base can alleviate the plume-induced shock wave and separation phenomenon and improve the control of the missile body.dy.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.3
• /
• pp.31-40
• /
• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• 유체기계공업학회:학술대회논문집
• /
• 1999.12a
• /
• pp.179-186
• /
• 1999

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67), and to evaluate the performances of k-$\epsilon$ and Baldwin-Lomax turbulence models. A finite volume method is used for spatial discretization. And, the equations are solved implicitly in time with the use of approximate factorization. Upwind difference scheme is used for inviscid terms, but viscous terms are centrally differenced. The flux-difference-splitting of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. And, the results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, we conclude that k-$\epsilon$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost same.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.10a
• /
• pp.91-94
• /
• 2003

An experimental study has been carried out in a supersonic blow-down wind tunnel for examining the influence of streamwise vortices on normal shock-wave/boundary layer interaction. It has been reported by the earlier investigator the streamwise vortices generated by the blowing jets can significantly suppress the shock-induced separation and reduce the wave drag. The blowing jets generate the streamwise vortices with 45$^{\circ}$ angle in the spanwise direction. The shock waves are visualized by a Schlieren optical system. Appropriate measurement systems are provided for the characterization of shock wave/boundary layer interaction. The chamber pressure ratio and blowing pressure ratio are varied from 1.5 to 2.4 and 1.0 to 2.0 respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.12
• /
• pp.986-993
• /
• 2018

Lateral thrust jet has better maneuverability performance than the control surface like the conventional fin for attitude control or orbital transition of guided weapons. However, in the supersonic region, a jet interaction flow occurs due to the lateral thrust jet during flight, and a complicated flow structure is exhibited by the interaction of the shock wave, boundary layer flow, and the vortex flow. Especially, hit-to-kill interceptors require precise control and maneuvering, so it is necessary to analyze the effect of jet interaction flow. Conventional jet interaction analyses were performed under low altitude conditions, but there are not many cases in the case of medium altitude condition, which has different flow characteristics. In this study, jet interaction flow analysis is performed on the lateral jet controlled interceptor operating at medium altitude. Based on the results, the structural characteristics of the flow field and the changes of aerodynamic coefficient are analyzed.