• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.623-629
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• 2017

Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle's geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.71-81
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• 2017

When an integral pressurized water reactor is operated under low power conditions, once-through steam generator group operation strategy is applied. However, group operation strategy will cause nonuniform coolant flow distribution at the core inlet and lower plenum. To help coolant flow mix more uniformly, a flow mixing chamber (FMC) has been designed. In this paper, computational fluid dynamics methods have been used to investigate the coolant distribution by the effect of FMC. Velocity and temperature characteristics under different low power conditions and optimized FMC configuration have been analyzed. The results illustrate that the FMC can help improve the nonuniform coolant temperature distribution at the core inlet effectively; at the same time, the FMC will induce more resistance in the downcomer and lower plenum.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.282-287
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• 2004

Unielement combustion tests were conducted using coaxial bi-swirl injectors. Major experimental parameters were a recess length and a fuel-side swirl chamber. Combustion efficiency mainly depends on a mixing mechanism for the present coaxial swirl injectors. Low-frequency pressure excitations around 200Hz were observed for all injectors. However, dynamic behaviors considerably differ for an external and an internal mixing case controlled by a recess length. The internal mixing induces mixture to be biased at a specific frequency in a mass flow rate, which results in a relatively high amplitude of pressure fluctuations but results for the external mixing case show that fuel and oxidizer mixture flow carries more complicated, multiple wave characteristics due to broad mixing region as well as disintegration and merging phenomena of propellant films.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.88-93
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• 2000

In this study, the mixing process of two-phase flow generated by two jets with height difference is analyzed. The primary jet is jetted on the condition of the state mixed pulverized solid particles with air. The height difference between the main jet and the secondary jet is changed into three kinds(0, 32.5, 47.5mm). The velocity vector field, concentration field and turbulent properties of solid particles are measured by using 3-Dimensional Particles Dynamics Analyzer. As the height difference of two jets through the two nozzles increases, the solid particle recirculation zone and the dense zone in the combustion chamber become large. The solid particle concentration at the center of the combustion chamber gets dense because the particle velocity remains slow due to the existence of the solid particle recirculation zone. The particle concentration in the combustion chamber can also be influenced by the hight difference of two jets.

• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1811-1820
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• 2005

Thermo-acoustic instability of methane/ air flames in an industrial gas-turbine combustor is numerically investigated adopting CFD analysis. The combustor has 37 EV burners through which methane and air are mixed and then injected into the chamber. First, steady fuel! air mixing and flow characteristics established by the burner are investigated by numerical analysis with single burner. And then, based on information on the flow data, the burners are modeled numerically via equivalent swirlers, which facilitates the numerical analysis with the whole combustion system including the chamber and numerous burners. Finally, reactive flow fields within the chamber are investigated numerically by unsteady analysis and thereby, spontaneous instability is simulated. Based on the numerical results, scaling analysis is conducted to find out the instability mechanism in the combustor and the passive control method to suppress the instability is proposed and verified numerically.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.417-424
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• 2009

A micro-mixer with a quasi-active rotor was fabricated, and mixing characteristics were evaluated. The proposed micro-mixer combines an active type micro-mixer with a passive type micro-mixer. The micro-rotor, which is a moving part of an active type micro-mixer, is added in a micro-chamber of a passive type vortex micro-mixer. The rotor rotated by inflows tangent to a chamber, causing strong perturbations. The micro-mixers were fabricated using photosensitive glass. Mixing efficiency of the micro-mixers was measured using an image analysis method. Mixing efficiency and characteristics of the micro-rotor mixer were compared with the vortex micro-mixer without a rotor. Mixing efficiency was reduced as Reynolds number increased at a low Reynolds number due to decrease of residence time. Mixing efficiency at higher Reynolds number, on the other hand, was improved even though residence time decreased since the contact surface between fluids increased by twisted flow. The perturbation induced by rotating rotor at greater than Re 200 improved the efficiency of the rotor mixer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.905-914
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• 2001

A large eddy simulation(LES) is performed for turbulent flow around a bluff body inside a sudden expansion cylinder chamber, a configuration which resembles a premixed gas turbine combustor. To promote turbulent mixing and to accommodate flame stability, a flame holder is installed inside the combustion chamber. The Smagorinsky model is employed and the calculated Reynolds number is 5,000 based on the bulk velocity and the diameter of the inlet pipe. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The predicted turbulent statistics are evaluated by comparing them with the laser-doppler velocimetry (LDV) measurement data. The agreement of LES with the experimental data is shown to be satisfactory. Emphasis is placed on the time-dependent evolutions of turbulent vortical structure behind the flame holder. The numerical flow visualizations depict the behavior of large-scale vortices. The turbulent mixing process behind the flame holder is analyzed by visualizing the sectional views of vortical structure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.31-34
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• 2011

Design and fabrication of Technology Demonstration Model(TDM) of 75 tonf regenerative cooling thrust chamber were described. It has design chamber pressure of 60 bar, propellant mass flow rate of 243.6 kg/s, and nozzle expansion ratio of 12. It has a single welded structure of the mixing head and the chamber. Design and fabrication technologies established through this TDM can be used to development of flight model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.391-398
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• 2008

LES analysis was conducted with in-house CFD code to investigate the turbulence evolution and interaction due to turbulence ring and splash plate in the gas generator. Though chemical reaction was not accounted for, the results can be useful in determining the turbulence characteristics generated by ring and plate. The calculation results show that the installation of turbulence ring can introduce additional turbulences and improve turbulent mixing in the downstream flow. However, the addition of splash plate in the downstream of TR brings totally different shape of perturbation energy and enstrophy distribution for turbulent mixing. This enhancement can be done by the formation of the intensively strong vorticity production and mixing behind the plate. Pressure drop was found to be a reasonable level of about 1% or less of initial pressure in all calculation cases. Also, calculation results revealed that the variation of TR shape and intrusion length did not change the characteristics of turbulent mixing in the chamber. Even though the effect of installation location of splash plate on the turbulent mixing is not investigated yet, calculation results conclude the addition of splash plate leads to the increase in turbulent mixing with an acceptable pressure drop.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.680-685
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• 2008

The ejector is a simple device which can transport a low-pressure secondary flow by using a high-pressure primary flow. In general, it consists of a primary driving nozzle, a mixing section, and a diffuser. The ejector system entrains the secondary flow through a shear action generated by the primary jet. Until now, a large number of researches have been made to design and evaluate the ejector systems, where it is assumed that the ejector system has an infinite secondary chamber which can supply mass infinitely. However, in almost all of the practical applications, the ejector system has a finite secondary chamber implying steady flow can be possible only after the flow inside ejector has reached an equilibrium state after the starting process. To the authors' best knowledge, there are no reports on the starting characteristics of the ejector systems and none of the works to date discloses the detailed flow process until the secondary chamber flow reaches an equilibrium state. The objective of the present study is to investigate the starting process of an ejector-diffuser system. The present study is also planned to identify the operating range of ejector-diffuser systems where the steady flow assumption can be applied without uncertainty. The results obtained show that the one and only condition in which an infinite mass entrainment is possible is the generation of a recirculation zone near the primary nozzle exit. The flow in the secondary chamber attains a state of dynamic equilibrium at this point.