• Proceedings of the Korean Society of Rheology Conference
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• 2001.09a
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• pp.161.1-161
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• 2001

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.181-188
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• 2005

Large eddy simulation(LES) methodology used to model the isothermal swirling flows in a dump combustor and the turbulent premixed flame in a model gas turbine combustor. The LES solver was implemented on parallel computer consisting 16 processors. In isothermal flow simulation, the results was compared with that of ${\kappa}-{\varepsilon}$ model as well as experimental data, in order to verify the capability of LES code. To model the turbulent premixed flame in a gas turbine, the G-equation flamelet model was used. The results showd that LES and RANS well predicted the mean velocity field of a non-swirling flow. However, in swirling flow, LES showed a better performance in predicting the mean axial and azimuthal velocities, and the central recirculation zone than those of RANS. In a model gas turbine combustor, the operation condition of high pressure and temperature induced the different phenomena, such as flame length and flow-field information, comparing with the condition of ambient pressure and temperature. Finally, it was identified that the flame and heat release oscillations are related to the vortex shedding generated by swirl flow and pressure wave propagation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.991-997
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• 2014

This study investigated the swirling flow fields of a gun-type gas burner (GTGB) without a combustion chamber under cold flow conditions. Three velocity components and the static pressure were measured with a straight-type five-hole pressure probe (GHPP) using a non-nulling calibration method and compared with the results of an X-type hot-wire probe (X-probe) and computational fluid dynamics (CFD). The GHPP measured the velocity and static pressure for the swirling flow of the central region of the GTGB better than the X-probe but produced slightly worse results than the CFD.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1290-1298
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• 2003

The stirred tank reactor is one of the most commonly used devices in industry for achieving mixing and reaction. Here we report on results obtained from the large eddy simulations of flow inside the tank performed using a spectral multi-domain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PlY measurements (Hill et al. $^{(1)}$) along with the theoretical model of the impeller-induced flow (Yoon et al. $^{(2)}$) were used in defining the impeller-induced flow as superposition of circumferential, jet and tip vortex pair components. Large eddy simulation of flow in a stirred tank was carried out for the three different Reynolds numbers of 4000, 16000 and 64000. The effect of different Reynolds numbers is well observed in both instantaneous and time averaged flow fields. The instantaneous and mean vortex structures are identified by plotting an isosurfaces of swirling strength for all Reynolds numbers. The Reynolds number dependency of the non-dimensional eddy viscosity, resolved scale and subgrid scale dissipations is clearly shown in this study.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.113-122
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• 2002

The purpose of this study is to verify that the modified Lagrangian model can predict temperature, flow and scalar fields in the high temperature recirculation region of swirling confined diffusion flame. In the meantime numerical results from EBU and Equilibrium PDF models as well as experimental results are compared with those from the modified Lagrangian model. Adaption of three different turbulent models were accompanied with this procedure. Look-up table of the ignition characteristic time scale which is one of important factors of the Lagrangian model was referred to the 11-step reduced mechanism. Eventually, results with the Lagrangian model show a good accordance with experimental results, which shows the validity of this model. Results from Chen's model differ from those of the others. Numerical results of ${\widetilde{k}$ show significant deviation from experimental results for three models.

• Korea-Australia Rheology Journal
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• v.16 no.2
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• pp.101-108
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• 2004

The hemodynamics behavior of the blood flow is influenced by the presence of the arterial stenosis. If the stenosis is present in an artery, normal blood flow is disturbed. In the present study, the characteristics of pulsatile flow in the blood vessel with stenosis are investigated by the finite volume method. For the validation of numerical model, the computation results are compared with the experimental ones of Ojha et al. in the case of 45％ stenosis with a trapezoidal profile. Comparisons between the measured and the computed velocity profiles are favorable to our solutions. Finally, the effects of stenosis severity and wall shear stress are discussed in the present computational analysis. It can be seen, where the non-dimensional peak velocity is displayed for all the stenosis models at a given severity of stenosis, that it is exponentially increased. Although the stenosis and the boundary conditions are all symmetric, the asymmetric flow can be detected in the more than 57％ stenosis. The instability by a three-dimensional symmetry-breaking leads to the asymmetric separation and the intense swirling motion downstream of the stenosis.

• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.82-91
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• 2003

The study of swirl flow has been of technical and scientific interest because it has an internal recirculation field and its tangential velocity is related to the curvature of the streamline. The fluid flow for ducts or elbows of an internal engine has been much studied through numerical methods and experiments, but studies about swirl flow has been insufficient. Using the PIV (Particle Image Velocimetry) method, this study found the time-mean velocity distribution, time-mean turbulent intensity, with swirl and without swirl flow for Re=10,000, 15,000, 20,000, and 25,000 along longitudinal sections and the results appear to be physically reasonable. In addition, axial velocity distribution is compared with that of Jeong's, Kodadadi's and Murakami's. It was found that the highest velocity of swirl and non-swirl flow occurs in the opposite position at the center of a round tube, $\phi$=45$^{\circ}$

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.3336-3344
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• 2014

The purpose of this study is small scale coagulation module is developed and demonstrated through a lab-scale test. Recent as a sewage treatment rate increases, have heightened the interest in the necessity on the nonpoint source and developing a small processing unit has been increased. Coagulation sedimentation module in this study is additional growth of floc through swirling in the outside zone, reduction of microstructure floc number and the internal settling zone through vertical/level flow complex sedimentation method after the coagulation process precipitation method as an effective high separation efficiency can be divided was also assessed. Coagulation sedimentation module can increase the load factor was 4.4 times compared to conventional clarifier base on the same volume and surface area through vertical/level flow. In this study, this process was selected formation and maintenance of swirling and uniform flow distribution in the internal settling zone as an important design factor, to derive its FLUENT was used to characteristics of the flow model. Through the simulation of swirling, influent velocity, dimensions of external basin, hopper depth of bottom cone was determined and through analysis of velocity distribution, flow distribution detailed specifications are derived like as diameter and number of effluent hole. Lab-scale($120{\ell}/hr$) test results, influent of 300~800 NTU to less than 10 NTU without polymer feeding was able to operate in the 20minutes retention time(surface loading rate $37.3m^3/m^2$-day), and through analysis FLUENT the possibility of using design parameters were derived.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1158-1174
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• 1988

A numerical technique is developed for the solution of fully developed turbulent recirculating flow in the passage of variable area using the non-orthogonal coordinate transformation. In the numerical analysis, primitive pressure-velocity finite difference equations were solved by SIMPLER algorithm with 2-equation turbulence model and algebraic stress model (ASM). QUICK scheme on the differencing of convective terms which is free from the inaccuracies of numerical diffusion has been applied to the variable grids and the results compared with those from HYBRID scheme. In order to test the effect of streamline curvatures on turbulent diffusion Lee and Choi streamline curvature correction model which has been obtained by modifying the Leschziner and Rodi's model is testes. The ASM was also employed and the results are compared to those from another turbulence model. The results show that difference of convective differencing schemes and turbulence models give significant differences in the prediction of velocity fields in the expansion region and outlet region of the combustor, however show little differences in the parallel flow region.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.1-2
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• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.