Nongradient diffusion in premixed turbulent flames

Recent theoretical and experimental results demonstrating the interaction between force fields and density inhomogeneities as they arise in premixed turbulent flames are discussed. In such flames, the density fluctuates between two levels, the high density in reactants rho sub r and the low density in products rho sub p, with the ratio rho sub r/rho sub p on the order of five to ten in flows of applied interest. The force fields in such flames arise from the mean pressure drop across the flame or from the Reynolds shear stresses in tangential flames with constrained streamlines. The consequence of the interaction is nongradient turbulent transport, countergradient in the direction normal to the flame and nongradient in the tangential direction. The theoretical basis for these results, the presently available experimental support therefore and the implications for other variable density turbulent flows are discussed

A provisional analysis of two-dimensional turbulent mixing with variable density

A predictive method for the titled flows based on the Prandtl energy method was developed and assessed by comparing predicted results with experimental results. For constant-density flows, both gross properties such as spreading rate and maximum turbulent kinetic energy and detailed properties such as mean shear stress distributions are shown to be well predicted. For variable-density flows, considerable attention is devoted to the inclusion in the analysis of the added effect of pressure fluctuations and of the variation in the several extant empirical parameters on the turbulent kinetic energy. It is found that a variation with Mach number of the characteristic Reynolds number for turbulent transport is needed to account for the observed decrease in spreading rate. The predictions which result from these considerations are compared with the limited experimental data presently available for the two crucial cases: compressible adiabatic mixing and low-speed isothermal mixing of two dissimilar gases

Laminar boundary layer on a cone in supersonic flow with uniform mass transfer

Laminar boundary layer solution on cone in supersonic flow with uniform mass transfe

Heat and mass transfer at a general three- dimensional stagnation point

Simultaneous effects of heat and mass transfer on boundary layer properties at three-dimensional stagnation point flow

Laminar boundary layer on a cone with uniform injection

Laminar compressible boundary layer on cone with uniform injectio

Further results related to the turbulent boundary layer with slot injection of helium

Data from an experiment involving the slot injection of helium into a turbulent boundary layer in air are analyzed in terms of unconditioned and conditioned Favre-averages. The conditioning is based on two levels of helium concentration so that the contributions to the unconditioned statistics from air, helium, and mixture of these two gases can be determined. The distributions of intermittency associated with the two helium levels establish the domains of influence of air, helium, and mixture

Momentum Transfer by Laser Ablation of Irregularly Shaped Space Debris

Proposals for ground-based laser remediation of space debris rely on the creation of appropriately directed ablation-driven impulses to either divert the fragment or drive it into an orbit with a perigee allowing atmospheric capture. For a spherical fragment, the ablation impulse is a function of the orbital parameters and the laser engagement angle. If, however, the target is irregularly shaped and arbitrarily oriented, new impulse effects come into play. Here we present an analysis of some of these effects.Comment: 8 pages, Proceedings of the 2010 International High-Power Laser Ablation Conferenc