• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1702-1710
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• 2001

Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.21-28
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• 2009

This experimental study was performed to find the important design parameters and the starting characteristics of a supersonic exhaust diffuser. The experimental study was carried out on a scaled down model of straight cylindrical supersonic exhaust diffuser, in order to evaluate the effects of operating fluid(air, nitrogen), the diffuser inlet area over the primary nozzle throat area($A_d/A_t$), the inlet pressure of primary nozzle, diffuser length over diffuser inner diameter($L_d/D_d$) and existence or nonexistence of diffuser divergence. The test results showed that the starting pressure increased with decrease in diameter of primary nozzle, and the measured starting pressure of the diffuser had approximately 90~98% efficiency as compared with the predicted starting pressure. Also, the diffuser was started at all case, regardless of $L_d/D_d$ (above 8.4) and diffuser divergence. The result of this study can be used as an essential database for developing a simulated high-altitude facility for real-scale model.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.1-8
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• 1999

In the present paper an attempt has been made to simulate the secondary injection-primary flow interaction in the conical rocket nozzle and to derive the performance of secondary injection thrust vector control(SITVC) system. Complex three-dimensional flowfield induced by the secondary injection is numerically analyzed by solving unsteady three-dimensional Euler equation with Beam and Warming's implicit approximate factorization method. Emphasized in the present study is the effect of secondary injection such as secondary mass flow rates and the momentum of secondary/primary nozzle flow mass rates upon the gross system performance parameters such as thrust ratio, specific impulse ratio and deflection angle. The results obtained in terms of system performance parameters show that lower secondary mass flow rate is advantageous for to reduce secondary specific impulse loss. It is further found that the nozzle with secondary jet injected downstream and interacting with fast primary flow is preferable for efficient and stable SITVC over the wide range of use with the penalty of side specific impulse loss.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.137-148
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• 2012

In pressurized water nuclear reactors, dissimilar metal welds are susceptible to primary water stress corrosion cracking. To access this problem, accurate estimation of welding residual stresses is important. This paper provides general welding residual stress profiles in dissimilar metal nozzle butt welds using finite element analysis. By introducing a simplified shape for dissimilar metal nozzle butt welds, changes in the welding residual stress distribution can be seen using a geometry variable. Based on the results, a welding residual stress profile for dissimilar metal nozzle butt welds is proposed that modifies the existing welding residual stress profile for austenitic pipe butt welds.

• Nuclear Engineering and Technology
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• v.52 no.11
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• pp.2638-2651
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• 2020

Nozzle corner cracks present at the intersection of reactor pressure vessels (RPVs) and inlet or outlet nozzles have been a persistent problem for a number of years. The fracture analysis of such nozzle corner cracks is very important and critical for the efficient design and assessment of the structural integrity of RPVs. This paper aims to perform an engineering critical assessment of RPVs with nozzle corner cracks subjected to several transients accompanied by pressurized thermal shocks. The critical crack size of the RPV model with nozzle corner cracks under transient loading is evaluated on failure assessment curve. In particular, the influence of cladding on the crack initiation of nozzle corner crack under thermal transients is studied. The influence of primary internal pressure and secondary thermal stress on the stress field at nozzle corner and SIF at crack front is analyzed. Finally, the influence of different crack size and crack shape on the final critical crack size is analyzed.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.283.1-283
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• 2001

• Journal of Power System Engineering
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• v.3 no.1
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• pp.23-28
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• 1999

Experimental and theoretical researches about jet pump have been carried out by many researchers. Jet pump can be used for the transportation of solid materials, farm produce, and fishes. It is the purpose of this paper to seek optimal multi nozzle shape of the annular jet pump. Experiments were done for several jet nozzle areas, jet nozzle arrays and jet nozzle lengths. Water was used for both the primary fluid and secondary fluid. The efficiency curves for the annular jet pump having multi nozzles are presented in this paper.

• Journal of Aerospace System Engineering
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• v.8 no.1
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• pp.30-35
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• 2014

This study has been conducted to develop an ejector system applied in the aircraft engine-bay ventilation system. Tandem-Ejector was selected as a component of ventilation system because it could achieve high ventilation performance in spite of motive flow with small flow rate. Tandem-Ejector is composed of a primary nozzle and two mixing ducts ($1^{st}$ mixing duct and $2^{nd}$ mixing duct). In this study, 1-D Tandem-Ejector model has been built with conservation laws and isentropic relation for 1-D ejector sizing and performance prediction. Computational Fluid Dynamics(CFD) has been conducted to investigate ejector performance and flow characteristics in the ejector. Also, Tandem-Ejector performance tests have been conducted to obtain ejector pumping performance and to investigate stand-off (gap between primary nozzle and $1^{st}$ mixing duct inlet) effect on ejector pumping performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.251-253
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• 2017

Numerical study of air-blast type injector for low emission aircraft engines was conducted. Volume-of-fluids approach was used to track interface of fuel and air. Primary atomization of fuel stream was visualized, and thickness and mean velocity at the injector exit was calculated. Liquid fuel injected from fuel slots joined together as a thin film on preflimer surface, and interacted with swirling air. As instability on the fuel surface increased, separation of fuel as ligaments and droplets occured. The film thickness and velocity were used to as fuel injection boundary condition for reactive flow simulation. Primary reaction zone was formed in vicinity of the fuel nozzle, creating a stable flame inside the combustor.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.130-140
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• 2014

Rotary kiln burner has been developed continuously to improve process efficiency and exhaust emission. In this study, the characteristics of the flame and exhaust emission were numerically analyzed according to the diameter of primary air nozzle, equivalent ratio of burner, and equivalent ratio at center and side nozzle for development of multi-nozzle burner in the COG(Coke Oven Gas) rotary kiln for sintering iron ore. The results indicated that the flame length and $NO_x$ emission increase, as the diameter of primary air nozzle and equivalent ratio of burner increase. And according to the change of equivalent ratio at the center and the side of the nozzle, the flame length and average temperature in the kiln show very little change but the $NO_x$ emission shows obvious difference. In conclusion, the best design conditions which have satisfying flame length, average temperature and $NO_x$ emission are as follows: $D_2/D_1$ is 1.33, equivalent ratio of burner is 1.25 and center nozzle conditions are Rich.