Numerical calculations of the aqueous humor dynamics in the anterior chamber of a rabbit's eye are presented to delineate the basic flow mechanisms. The calculations are based on a geometrical model of the eye, which represents the Trabecular meshwork (TM) as a multilayered porous zone of specified pore sizes and void fraction. The outer surface of the cornea is assumed to be at a fixed temperature (corresponding to the ambient temperature), while the iris surface is assumed to be at the core body temperature. Results are obtained for both the horizontal upward-facing orientation of the eye, and the vertical orientation of the eye. Parameters varied include: the temperature difference between the iris and the cornea to underscore the important role of buoyancy in driving the aqueous humor flow; and, the pupil size reflecting different levels of ambient light. Buoyancy is observed to be the dominant driving mechanism for the convective motion in both orientations of the eye. Variations in the pupil size appear to have little influence on the IOP or flow distribution in view of the dominant role of buoyancy in controlling the flow motion. The study provides distributions of the shear stress and flow patterns and delineates the important role of the eye-orientation on these results.
Predictions of turbine blade film cooling have traditionally employed Reynolds-averaged Navier-Stokes solvers and two-equation models for turbulence. Evaluation of several versions of such models have revealed that the existing two-equation models fail to resolve the anisotropy and the dynamics of the highly complex flow field created by the jet-crossflow interaction. A more accurate prediction of the flow field can be obtained from large eddy simulations (LES) where the dynamics of the larger scales in the flow are directly resolved. In the present paper, such an approach has been used, and results are presented for a row of inclined cylindrical holes at blowing ratios of 0.5 and 1 and Reynolds numbers of 11,100 and 22,200, respectively, based on the jet velocity and hole diameter. Comparison of the time-averaged LES predictions with the flow measurements of Lavrich and Chiappetta (UTRC Report No. 90-04) shows that LES is able to predict the flow field with reasonable accuracy. The unsteady three-dimensional flow field is shown to be dominated by packets of hairpin-shaped vortices. The dynamics of the hairpin vortices in the wake region of the injected jet and their influence on the unsteady wall heat transfer are presented. Generation of “hot spots” and their migration on the film-cooled surface are associated with the entrainment induced by the hairpin structures. Several geometric properties of a “mixing interface” around hairpin coherent structures are presented to illustrate and quantify their impact on the entrainment rates and mixing processes in the wake region.
SwirlPremixed combustion Premixedness a b s t r a c tThe effect of swirl, premixedness and geometry has been investigated for hydrogen enriched premixed flame using Large Eddy Simulation (LES) with a Thickened Flame (TF) model. Swirl strength has been varied to study the effects of swirl on flame behavior in a laboratory-scale premixed combustor operated under atmospheric conditions. In addition, the levels of premixedness and geometry have also been changed to study the role of these quantities on flame behavior. The turbulent flow field and the chemistry are coupled through TF model. In the LES-TF approach, the flame front is resolved on the computational grid through artificial thickening and the individual species transport equations are directly solved with the reaction rates specified using Arrhenius chemistry. Good agreement is found when comparing predictions with the published experimental data including the predicted RMS fluctuations. Also, the results show that higher swirl strength and increase in level of premixedness make the system more susceptible to upstream flame movement due to higher combustibility of hydrogen, which increases the reaction along the flame front, thereby raises temperature in the reaction zone and leads to combustion induced vortex breakdown (CIVB). Moreover, upstream flame movement is always observed at higher swirl strength irrespective of level of premixedness and burner geometry, whereas the premixed systems exhibit stable behavior while operating at low swirl.
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