A combined experimental and computational study was conducted to investigate the effect of fuel density variations on mixing from a double annular counter-rotating swirl (DACRS) nozzle operated at atmospheric pressure under non-reacting conditions using either helium (He) or a mixture of He and CO2 as fuel simulants. A small probe traversed through the flow collecting gas samples that were sent to gas analyzers measuring the concentration profiles. The resulting measurements are then used to validate the computational fluid dynamics (CFD) model. A commercial CFD code (CFX 10) with a Reynolds averaged Navier-Stokes (RANS) formulation was used to simulate the experiment. Multiple turbulence closures, such as standard and realizable k-ε and SSG Reynolds stress model were evaluated. Additionally, several geometrical considerations, such as modeling a 72° sector versus a full 360°, were tested. While at high fuel-to-air momentum flux ratios (J) the fuel simulant concentration profiles were outward-peaked, and at low J the profiles were center-peaked. An analysis of the experimental results clearly indicate the momentum flux ratio is the most influential parameter controlling mixing in a DACRS nozzle. The simulations produced quantitative agreement with the experimental measurements using the realizable k-ε turbulence closure and only modeling a 72° sector of the nozzle. The complexity of the studied problem required a considerable refinement of the grid to produce an accurate and grid independent solution. The validated model may now be used to explore the design space for optimization of a nozzle for utilization in a syngas application.
By embedding a dissociating material into the porous outer structure of a projectile, stagnation-point heat transfer may be reduced by transpiration cooling resulting from the outflow of the dissociated gas products. The principal material considered is ammonium chloride, NHLjCl, which dissociates at temperatures over 613 K, hence providing additional heat-transfer reduction. Stagnation-point heat-transfer solutions for the injection of the dissociation products of NH^Cl into both equilibrium and frozen boundary layers are presented and compared with those for the injection of other gases such as helium. Results show that dissociative cooling has the potential to provide a significant reduction in stagnation-point heat transfer as temperatures rise, because the gas injection rate increases with the temperature of the NH4C1 interface.
NomenclatureCi = mass fraction, p//p c p = specific heat per unit mass at constant pressure c p = mass-average specific heat of gas mixture D -multicomponent diffusion coefficient T) = binary-diffusion coefficient / = quantity defined by Eq. (8) h = enthalpy 7 = diffusive mass flux k = thermal conductivity I = pn/(pn)u, Le = Lewis number, D p c p /k M -molar mass ___ M = blowing parameter, p w v w /^/p e^e K N = molar flux Nu = Nusselt number, q" w x/(T e ~ T w )k P = pressure Pr -Prandtl number, H,C P /K q" = heat flux R -gas constant r = cylindrical radius Re = Reynolds number, u e x/v T = temperature u = x -component velocity v = ^-component velocity x = distance along body surface y = distance normal to body surface s = well depth in intermolecular potential r) = transformation defined by Eq. (6) 9 = T/T e K = velocity gradient, du e /8x IJL = viscosity v = kinematic viscosity £ = transformation defined by Eq. (7) p = density a = collision diameter $>ij = function of molar masses, ^Mj/M t 0 = porosity
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