Assessment of Finite Rate Chemistry Large Eddy Simulation Combustion Models.

Large Eddy Simulations (LES) of a swirl-stabilized natural gas-air flame in a laboratory gas turbine combustor is performed using six different LES combustion models to provide a head-to-head comparative study. More specifically, six finite rate chemistry models, including the thickened flame model, the partially stirred reactor model, the approximate deconvolution model and the stochastic fields model have been studied. The LES predictions are compared against experimental data including velocity, temperature and major species concentrations measured using Particle Image Velocimetry (PIV), OH Planar Laser-Induced Fluorescence (OH-PLIF), OH chemiluminescence imaging and one-dimensional laser Raman scattering. Based on previous results a skeletal methane-air reaction mechanism based on the well-known Smooke and Giovangigli mechanism was used in this work. Two computational grids of about 7 and 56 million cells, respectively, are used to quantify the influence of grid resolution. The overall flow and flame structures appear similar for all LES combustion models studied and agree well with experimental still and video images. Takeno flame index and chemical explosives mode analysis suggest that the flame is premixed and resides within the thin reaction zone. The LES results show good agreement with the experimental data for the axial velocity, temperature and major species, but differences due to the choice of LES combustion model are observed and discussed. Furthermore, the intrinsic flame structure and the flame dynamics are similarly predicted by all LES combustion models examined. Within this range of models, there is no strong case for deciding which model performs the best.

Immunoreactive alpha and beta subunits of follicle stimulating and luteinizing hormones in peripheral blood throughout the menstrual cycle and following stimulation with synthetic gonadotropin releasing hormone (GnRH).

The concentration of immunoreactive alpha and beta subunits of human LH (hLH) and human FSH (hFSH) were measured in unfractionated serum throughout normal menstrual cycles, and when GnRH was administered at about midcycle. The RIA subunit systems employed were sufficiently sensitive and specific to measure basal levels of free alpha-hLH, beta-hLH, and alpha-hFSH. The beta-hFSH system lacked sufficient sensitivity to measure beta-hFSH in unfractionated serum. In normal cycles, alpha-hLH, beta-hLH and alpha-hFSH were shown to circulate in the free form with highest concentrations occurring at the time of midcycle peak of LH and FSH. The concentration of subunits during the follicular phase were not significantly different from those observed during the luteal phase of the cycle. In response to GnRH administration during the periovulatory phase of the cycle, the increases in circulating free alpha-hLH, beta-hLH, and of alpha-hFSH subunits were directly related to the increases in LH and FSH. Other investigators have shown that increases in circulating levels of free subunits are due to secretion from the pituitary gland rather than from peripheral dissociation of intact hormone. Therefore, it can be assumed that the increase in immunoreactive alpha-hLH, beta-hLH, and of alpha-hFSH subunits observed in this study at midcycle represent release of free subunits in response to endogenous or exogenous GnRH administration.