• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.10
• /
• pp.649-657
• /
• 2017

A rupture in a high-pressure pipe causes the fluid in the pipe to be discharged in the atmosphere at a high speed resulting in a supersonic jet that generates the compressible flow. This supersonic jet may display complicated and unsteady behavior in general. In this study, Computational Fluid Dynamics (CFD) analysis was performed to investigate the compressible flow generated by a supersonic jet ejected from a high-pressure pipe. A Shear Stress Transport (SST) turbulence model was selected to analyze the unsteady nature of the flow, which depends upon the various gases as well as the diameter of the pipe. In the CFD analysis, the basic boundary conditions were assumed to be as follows: pipe of diameter 10 cm, jet pressure ratio of 5, and an inlet gas temperature of 300 K. During the analysis, the behavior of the shockwave generated by a supersonic jet was observed and it was found that the blast wave was generated indirectly. The pressure wave characteristics of hydrogen gas, which possesses the smallest molecular mass, showed the shortest distance to the safety zone. There were no significant difference observed for nitrogen gas, air, and oxygen gas, which have similar molecular mass. In addition, an increase in the diameter of the pipe resulted in the ejected impact caused by the increased flow rate to become larger and the zone of jet influence to extend further.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.261-267
• /
• 2005

The unsteady flow analysis of staging system is conducted. This study focuses on comparing the results of two different governing equations between Euler equations and Navier-Stokes equations. The Chimera grid scheme is applied to moving simulations for unsteady flow analysis with dynamic simulation. As a result, it is certified that inviscid simulation have capabilities enough to analyze the present staging problem.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.2
• /
• pp.23-28
• /
• 2011

The engine ground and altitude tests were carried out to investigate the effect of jet fuel alteration on the performance of a small turbojet engine. JP-S was supplied 8% higher than JP-8 by fuel metering system at the same command. The employment of JP-S showed the similar starting characteristic to that of JP-8, however, difference in the ignition time and acceleration rate of engine speed due to the difference of fuel flow rate by fuel metering system was observed. In spite of jet fuel alteration, the test results yield the similar steady-state engine performance in net thrust, air flow, exhaust gas temperature, etc. On the other hand, the fuel consumption of JP-S increased by 5 % compared with that of JP-8. In point of specific fuel consumption (SFC), SFC of JP-S was approximately 1.1~2.6 %, 5 % higher than that of JP-8 in ground and altitude tests respectively at the same thrust.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.101-108
• /
• 2002

A numerical simulation of an incompressible cavity flow is conducted. Two dimensional Navier-Stokes equations are integrated using staggered grid and a finite volume method with C-QUICK scheme for spatial derivatives and fully implicit scheme for the time derivatives. SIMPLE-C algorithm is employed to solve the pressure field. Computational results show that the third eddy is generated in the shear layer mode but not in the steady mode. This signifies that the third eddy plays an important role in cavity flow stability. As a means to control the flow, jet blowing is applied to a position below the cavity upstream edge. Effects of flow control parameters on the stability such as the frequency, the phase, and the velocity magnitude are reported.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.3
• /
• pp.301-310
• /
• 2013

Jet fans are installed in road tunnels in order to maintain critical velocity when fire occurs. Generally the number of jet fans against fire are calculated by considering critical velocity and flow resistance by wall friction, vehicle drag force, thermal buoyance force and natural wind. In domestic case, thermal buoyance force is not considered in estimating the number of jet fans. So, in this study, we investigated the pressure loss due to the thermal buoyance force induced by tunnel air temperature rise and the impact of thermal buoyance force on the number of jet fans by the numerical fire simulation for the tunnel length(500, 750, 1000, 1500, 2000, 3500m) and grade (-1.0, -1.5, -2.0%). Considering the thermal buoyance force, number of jet fans have to be increased. Especially in the case of 100MW of heat release rate, the pressure loss due to thermal buoyance force exceed the maximum pressure loss due to vehicle drag resistance, so it is analyzed that number of 2~11 jet fans are needed additionally than current design criteria. Thus, in case of estimating the number of jet fans, it must be considered of thermal buoyance force induced tunnel air temperature rise by fire.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.310-313
• /
• 2006

The present study aims at investigating the effectiveness of a new passive cavity flow control technique, sub-cavity. The characteristics of cavity flow oscillation with the device are compared with those with other control techniques tested previously, including a triangular bump and blowing jet. In the computation, the three-dimensional, unsteady Navier-Stokes equations governing the supersonic cavity flow are solved based on an implicit finite volume scheme spatially and multi-stage Runge-Kutta scheme temporally. Large eddy simulation (LES) is carried out to properly predict the turbulent features of cavity flow. The present results show that the pressure oscillation near the downstream edge dominates overall time-dependent cavity pressure variations, and the amplitude of the pressure oscillation can be reduced in the presence of a sub-cavity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2005.11a
• /
• pp.117-120
• /
• 2005

The present study describes unsteady flow phenomena generated in a supersonic flow passing over a rectangular cavity and suggests a way of control of pressure oscillation, doing harm to overall performance and stable operation of aerodynamic and industrial applications. The three-dimensional, unsteady, compressible Navier-stokes equations are numerically solved based on a fully implicit finite volume scheme and large eddy simulation. The cavity flow are simulated with and without control methods, including a triangular bump and blowing jet installed near the leading edge of the cavity. The results show that the pressure oscillation is attenuated by both control techniques, especially near the trailing edge of cavity.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.5
• /
• pp.118-126
• /
• 2002

The Altitude Engine Test Facility(AETF) was built at the Korea Aerospace Research Institute and has been being operated for the gas turbine engines in the class of 3,000 lbf thrust. To enhance the confidence level of AETF to the international level, a series of studies and facility modification have been conducted to improve the measurement uncertainty and reliability. In this paper, some part of the facility evaluation tests performed with a single spool turbojet engine are introduced. Tests were performed simulating the flight conditions as steady state, sea level for various flight speeds (i.e., Mn=0.3, 0.5, 0.7, 0.9). The obtained test results are compared with the predicted values of the engine DECK. The measurement uncertainties of airflow, net thrust, fuel flow and SFC showed 0.791~0.914%, 0.851~1.706%, 1.372~7.348% and 1.642~5.205%, respectively. Thus, from this research, the improvement methods of uncertainties on AETF has been confirmed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.11-11
• /
• 1998

다목적으로 활용할 수 있는 터보축 엔진의 개발을 위한 정상상태 및 동적모사 프로그램을 개발하였다. 개발비, 개발시간, 개발위험도의 절감을 위해 가스발생기 부분은 성능이 잘 알려진 기존의 터보제트 엔진을 활용하였으며 약 3000hr 이상의 수명을 확보하기 위해 터빈재질을 교체하고, Larson-Miller 곡선을 이용하여 최대회전속도와 최대 터빈 입구온도를 각각 35000 RPM과 1140 K의 결정하였다 추가되는 동력터빈의 구성품 성능선도는 압축기 터빈 성능선도를 축척하여 사용하였다. 정상상태 성능해석에는 유량 및 일평형 방정식을 이용하였으며, 동력터빈이 각각 73%, 80%, 90%, 100% RPM일 때 가스발생기를 75%(24500 RPM)에서 100%(35000 RPM)까지 5% 간격으로 나누어 계산을 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.7
• /
• pp.2386-2396
• /
• 1996

A numerical simulation has been performed for isothermal and reacting flows in an exisymmetric, bluff-body research combustor. The present formulation is based on the density-weighted averaged Navier-Stokes equations together with a k-epsilon. turbulence model and a modified eddy-breakup combustion model. The PISO algorithm is employed for solution of thel Navier-Stokes system. Comparison between measurements and predictions are made for a centerline axial velocities, location of stagnation points, strength of recirculation zone, and temperature profile. Even though the numerical simulation gives acceptable agreement with experimental data in many respects, the present model is defictient in predicting the recoveryt rate of a central near-wake region, the non-isotropic turbulence effects, and variation of turbulent Schmidt number. Several possible explanations for these discrepancies have been discussed.