Sang-Hyeon Lee

Computational investigation of shock-enhanced mixing and combustion

A computational investigation of shock-enhanced mixing and combustion is presented. To understand the influences of the mixing process on the combustion process, the mixing characteristics of the reacting case are compared with those of the nonreacting case. Parametric studies varying the conditions of fuel injection are conducted to find the trends of the mixing and combustion processes. Three-dimensional Navier-Stokes equations with a chemical reaction model and κ-ω turbulence model are used. The upwind method of Roes flux difference splitting scheme is adopted. It is shown that the mixing process has a strong influence on the combustion process, whereas the combustion process does not have any significant effect on the mixing process. The combustion process is divided into two mixing regimes: a convection-dominated regime, where the burning rate increases with distance from the injection plane, and a diffusion-dominated regime as one moves downstream, where burning rate is constant. In the parametric studies, varying the fuel pressure with the fuel density held fixed makes little difference, whereas varying the fuel density makes a significant difference in mixing rate and burning rate. A prediction of minimum combustor length for complete combustion is made.

Computational Investigation of Shock-Enhanced Mixing: Application to Circular Cross Section Combustor

A computational investigation of shock-enhanced mixing applied to circular cross section combustors is presented. In a circular cross section combustor, there are shock wave intersections at the center axis that produce adverse effects on mixing characteristics. The purpose of this investigation is to analyze the adverse effects due to the shock wave intersections and to develop new combustor geometry minimizing the adverse effects and improving the mixing characteristics. Three-dimensional Navier-Stokes equations are used to calculate the motion of the mean flow. A κ-ω turbulence model is used to calculate the turbulent viscosity. It is shown that, in a circular cross section combustor, the shock waves intersecting at the center axis reduce the strength of the longitudinal vorticity and push the fuel downward. A change in the shape of the cross section of the combustor to an octagonal cross section results in a reduction of the adverse effects and an improvement of the mixing characteristics.

Thermal Vacuum Test of Kaistsat-4 Qm

KAISTSAT- 4, an experimental small satellite, is being developd by Satellite Technology Research Center in KAIST as a sequel mission to KITSAT-1, 2, and 3. The flight model scheduled to be launched in 2003, the qualification model construction and testing have been completed recently. The satellite subsystems of the qualification model have been tested under a thermal vacuum environment harsher than expected in the orbit. Thermal balance test has also been done in order to evaluate and tune the thermal analysis model of the qualification model. This paper describes the thermal vacuum test procedure, the results, as well as the lessons learned during the tests, which can be useful for future thermal vacuum tests of small satellites.

Application of shock-enhanced mixing to circular cross-sectional combustor

Re u,v,w A computational investigation on shock-enhanced mixing applied to a circular cross-sectional combustor 7 is presented. In a circular cross-sectional combustor, x there exist the shock intersections through the center y axis that produce adverse effects on mixing z characteristics. The purpose of this investigation is to x,y,z analyze the adverse effects of the shock intersection, Y and to develop a new combustor geometry for zj minimizing adverse effects and improving mixing characteristics. The three-dimensional thin-layer Navier-Stokes equations are used to calculate the motions of mean flow. The k-co turbulence model known for giving better prediction in compressible ^ flow is used. An upwind method of Roes flux P : difference splitting scheme is adopted to calculate co = mean and turbulence flow motions. It is shown that co = the shock intersected through the center axis reduces the strength of the longitudinal vorticity, and pushes Subscript the fuel down. A geometric modification is introduced to eliminate the adverse effects due to the shock intersection by removing unnecessary shock waves that do not make any contribution on shock-enhanced mixing. This geometric modification results in improving mixing characteristics and consequently reducing wave drag considerably. Reynolds number velocity components velocity of inlet air injectant to freestream velocity ratio streamwise coordinate cross-streamwise coordinate vertical coordinate coordinates normalized by A, mass fraction jet liftoff height, helium mass flux center normalized by A,general coordinates circulation normalized by «„ ht specific heat ratio injectant to freestream density ratio

Characteristics of Dual Transverse Injection in Supersonic Flow Fields II-Combustion Characteristics

Based on the analyses of the single transverse injection in supersonic flow fields, the mixing characteristics of dual transverse injection of hydrogen in supersonic air flow are studied with computational methods. Three-dimensional Navier -Stokes and the k- SST turbulence model were used. A parametric study is conducted with the variation of the distance between two injectors. The flow patterns and the mixing characteristics of two injection flows are very different from each other, and the flow patterns and the mixing characteristics of the rear injection flow are strongly influenced by those of the first injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of mixing rate and penetration of fuel. However, the increase of the distance over the specific distance results in the decrease of mixing rate and penetration of fuel. From the results it can be stated that there exists a distance between two injectors for optimum mixing characteristics.