Bok Jik Lee

Large Eddy simulations of a premixed jet combustor using flamelet-generated manifolds : effects of heat loss and subgrid-scale models

Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet-generated manifold technique for chemistry tabulation. The configuration is characterized by an off-center nozzle having an inner diameter of 10 mm, supplying a lean methane-air mixture with an equivalence ratio of 0.71 and a mean velocity of 90 m/s, at 573 K and atmospheric pressure. Conductive heat loss is accounted for in the manifold via burner-stabilized flamelets and the subgrid-scale (SGS) turbulence-chemistry interaction is modeled via presumed probability density functions. Comparisons between numerical results and measured data show that a considerable improvement in the prediction of temperature is achieved when heat losses are included in the manifold, as compared to the adiabatic one. Additional improvement in the temperature predictions is obtained by incorporating radiative heat losses. Moreover, further enhancements in the LES predictions are achieved by employing SGS models based on transport equations, such as the SGS turbulence kinetic energy equation with dynamic coefficients. While the numerical results display good agreement up to a distance of 4 nozzle diameters downstream of the nozzle exit, the results become less satisfactory along the downstream, suggesting that further improvements in the modeling are required, among which a more accurate model for the SGS variance of progress variable can be relevant.

Large eddy simulation of a turbulent premixed jet flame using flamelet-generated manifolds

Large eddy simulations of a turbulent premixed jet flame in a confined chamber were conducted using the flamelet generated manifold technique. The scope of the present research is to investigate the effects of inflow boundary conditions in these simulations. To evaluate the effect of two kinds of inflow boundary conditions, the numerical solutions using those boundary conditions are compared with experimental results. Turbulent flow generated by the self-recycling boundary condition behaves in a more realistic way, while randomly distributed perturbation imposed on the inlet boundary immediately vanished due to the lack of the turbulence structure. Quantitative comparison between experimental and computational results was carried out and analized.

Heat Flux Measurement Techniques over the protuberance at the hypersonic flow of Mach 7

An experimental investigation has been conducted on the aerodynamic heating caused by an object protruding from a flat plate at hypersonic flows of Mach 7. Three different experimental techniques are applied to measure the heat flux and temperature over the protuberance, using two types of hypersonic wind tunnels, namely, blowdown and impulse types. This paper presents the experimental tec hniques needed for use in hypersonic tunnels focusing on issues such as heat flux measurement techniques, as well as the measurement of detailed experimental data. It was confirmed that the data set agree well through the comparison of data results. A large separation region is observed in front of the protuberance with that region being very sensitive to the height of the protuberance and the length of the flat plate. These flow feat ures affect the aerodynamic heating over the protuberance. Basically, the measured heat flux is large when the height of the protuberance is large and the length of the flat plate is long. Also, the heat flux measurements at the upper positions are larger than at the lower positions. For high protuberances, a severe jump in the heat flux is observed, from about 0.6~0.7 of the height of the protuberances. However, when the protuberance is sufficiently short, a rise in the heat flux is rarely observed as the protuberance is submerged totally under the separation region upstream from the protuberance.

Numerical Simulation of Hypervelocity Flow on Hemisphere in T2 Shock Tunnel

Numerical simulations are thoroughly carried out for the flows in the nozzle and the test section in the T2 shock tunnel facility. In order to solve the flow realistically, an unsteady, axisymmetric, and nonequilibrium flow solver is employed. The thermochemical states of the gas are described by a four-temperature model. Obtained temperatures are compared with the experimental data measured by Palma using a Planar Laser-Induced Fluorescence (PLIF) Imaging technique.