• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.211-214
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• 2011

In the present work, a computational study was conducted to investigate characteristic of lateral force on the flow fields inside the propulsion nozzle with step. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST k-${\omega}$ turbulence model are solved using a fully implicit finite volume scheme. In order to simulate the shut-down process of the engine, NPR is varied from 100.0 to 10.0. It is observed that the separation point and Mach-disk strongly depend on the variation of NPR, and adjusting the step lead to significantly different characteristics in the lateral forces.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.570-573
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• 2012

Performance characteristics of subscale diffuser for high-altitude simulation have been numerically investigated. The length of diffuser entrance with respect to nozzle exit diameter was changed to 0, 50, 100%, respectively. In addition, flow characteristics have been studied for various length to diameter ratio of secondary throat diffuser. As a result, the shape of plume was contracted for insufficient length of diffuser entrance. Also, if the length to diameter ratio of secondary throat diffuser were less than 7 or 8, mach disk has been formed inside the diffuser.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.137-140
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• 2003

The flow characteristics of secondary recirculation region in a liquid fuel ramjet combustor are measured using PIV method. The model combustor has two rectangular inlets that form 90 degree angle each other. The tested angles of the air intakes were 30, 45 and 60. Three guide vanes are installed in each rectangular inlet to improve the flow stability. The experiments are performed in the water tunnel test with the same Reynolds number as the case of Mach 0.3 at the inlet. PIV software is developed to measure the characteristics of the flow field in the combustor. The accuracy of the developed PIV program is verified with rotating disk experiment and standard data. The experimental results show that the secondary recirculation flow occurred at the front junction of inlet main stream and combustorchamber. The size of secondary recirculation regions are increased with increasing air inlet angles. Since the performanceof combustor is very dependant on not only the main recirculation in the dome region but also the secondary recirculation flow in a junction region, the optimal angle of the air intakes should consider the both recirculation size as a frame holder.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.12
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• pp.913-919
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• 2015

A supercavitating vehicle has a speed of more than 300 km/h in water. A numerical analysis of the flow around a supercavitating vehicle must deal with a multiphase flow consisting of the water, vapor and exhaust gas because the vehicle is powered by roket propulsion. The effect of the exhaust gas on the vehicle is an important part in the study of the performance of the supercavitating vehicle. In the present study, the effect of the exhaust gas on the drag of vehicle was investigated by conducting numerical analysis. When there is no exhaust gas, drag of vehicle is affected by re-entrant. In the case with rocket propulsion, the exhaust gas reduces the influence of re-entrant. The exhaust gas also creates Mach disk and it changes drag profile.

• Journal of the Korea Institute of Military Science and Technology
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• v.4 no.2
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• pp.256-262
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• 2001

Viscous solutions of supersonic side jet nozzle and supersonic jet impinging on a flat plate are simulated using three-dimensional Navier-Stokes solver. For rapid and abrupt control of a missile in supersonic flight, side jet on a missile body is found to be a useful devise as evidenced by recent missile development at several nations. The magnitude of the side jet and the duration of it decide the level of control of such a missile system. The aerodynamic characteristics of the side jet devise itself are examined in terms of key parameters such as the side jet nozzle geometry, the chamber pressure and temperature. On the other hand, the jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. As the plate is placed close to the nozzle, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. The amplitude of wall pressure fluctuations subsides as the plate/nozzle distance increases, and the frequency of the wall pressure is estimated on the order of 10.0 KHz. Objectives of this paper are to show accurate simulation of nozzle flow itself and to demonstrate the jet flow structure when the jet interacts with a wall at a close range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.321-328
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• 2014

The performance characteristics of a subscale diffuser under non-reacting conditions for high-altitude simulation were numerically investigated with respect to different lengths of the secondary throat diffuser. The ratio of the length of the diffuser entrance to the nozzle exit diameter was set to 0, 50, and 100%. In addition, flow characteristics were studied for a range of length-to-diameter ratios of the secondary throat diffuser. An insufficient diffuser entrance length caused contraction of the plume immediately after the nozzle exit. When the length-to-diameter ratio was less than 8, a strong Mach disk was formed inside the diffuser, resulting in a sharp increase in pressure. In addition, flow characteristics in the diverging part of the diffuser were investigated for a range of diverging part lengths. A short diverging part may lead to abrupt pressure recovery, resulting in the possible application of mechanical load to the diffuser.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.281-285
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• 2007

The flow characteristics in the thruster should be analyzed considering its geometry and the pressure ratio to estimate its performance and etc. This paper suggests the computational result of an axisymmetric real nozzle for the altitude control of a satellite to find out the application limit that the assumption of continuum mechanics holds. The steady non-reacted compressible flow field in the unstructured grid system is computed and analyzed with varying the environmental pressure (or the degree of vacuum) under the fixed pressure ratio in a real thruster of which the area ratio of exit to throat is 56. The assumption of the continuum mechanics is not approved when the environmental pressure is reduced less than $10^{-3}$ atm.

• Journal of Aerospace System Engineering
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• v.12 no.5
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• pp.40-47
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• 2018

The objective of this study is to investigate the turbulence models with compressibility correction for large separation-flow in a supersonic convergent-divergent rectangular nozzle. As turbulence models, Yang and Shih's Low-Re $k-{\varepsilon}$ model, Mener's $k-{\omega}$ SST model and Wilcox's $k-{\omega}$model were evaluated. In order to get a significant compressible effects, Sarkar and Wilcox compressibility correction models were applied to the turbulence models respectively. Also, the simulation results were compared with experimental data. The turbulence model with compressibility correction model improves both of shock position and pressure recovery, but deteriorates the length of Mach disk.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.281-286
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• 2007

The Navier-Stokes equations are numerically solved for a two-dimensional small nozzle with the area ratio of 1.8 between the throat and the exit. The shock structures are verified inside the nozzle and near the exit varying with the pressure ratio and the length of the diverging part, respectively. Especially the irregular patterns in the pressure distribution near the throat are analyzed based on the geometric characteristics. It is found that there are similar phenomena in the shock wave structure between the pressure ratio and the length changes. Also there exists a normal shock just between two different oblique shocks crossing each other in special cases.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.6
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• pp.979-985
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• 2011

This paper includes that there are results of designing the flash hider and analyzing fluid dynamics of a front area of the barrel to shorten the length of small arms. Generally, the muzzle flash can be generated out of the barrel by the reaction between the oxygen in the air and unburned gunpowder contained in the propellant gas if a barrel is not long enough to burn gunpowder fully inside of the barrel. Though, the hugh muzzle flash, which is a characteristic of small arms with short barrel length, caused a soldier to aim at the target at night by making the soldier blind for a while and endangers his life by revealing firing position to enemies. Besides, the heat of muzzle flash can weaken the performance of thermal sights, which are attached to small arms for night battlefield. In this paper, flash hiders with several different shapes were designed for a newly developed 5.56mm caliber rifle with short barrel length. The performance of each flash hider to reduce the muzzle flash was compared theoretically and experimentally. Through the authorized test procedure, a highly efficient design of flash hider for reducing the muzzle flash was identified. The result of the paper can be helpful when designing flash hiders for small arms with short barrel length.