.GIF)
Turbomachinery Flow Codes Made Available to Industry
New Technique Calculates Properties of Surface Alloys for Immiscible Metals
Extended Mixing and Transition Control Theory Evaluated Numerically
Thermal Radiation Effects Analyzed in Semitransparent Materials
The computer code that solved for the time-averaged flow state existing within a typical passage of a blade row and the code for the associated unsteady flow state have been made available to industry. In addition, gas turbine manufacturers have begun to incorporate the average-passage flow model into their design systems. Results obtained by industry researchers clearly show the unique prediction capability of both the time-averaged and unsteady flow solvers.
Lewis contact: Dr. John J. Adamczyk, (216) 433-5829
Headquarters program office: OA
The experimental exploration of this class of materials requires specialized equipment and a great deal of effort. We have applied a new theoretical technique for calculating alloy properties: the Bozzolo, Ferrante, and Smith method (BFS) (ref. 2), invented at NASA Lewis to study these alloys. With a minor theoretical effort we were able to verify the experimental results-a surface alloy in the top atomic plane for coverages less than half a monolayer, no incorporation of the gold into the second layer, and phase separation for coverages greater than half a monolayer. We also examined a wide range of geometrical configurations that would be difficult to resolve experimentally. The illustration shows the preferred configuration from both the experiment and our predictions.
The efficiency of the BFS method will allow the examination of a multitude of possible materials, which, combined with ab-initio methods, will enable both the bonding and electronic properties of the materials to be determined. These efficient theoretical methods will aid in recommending the best candidate materials for various catalytic, structural bonding, and electronic applications.
References
Lewis contact: Dr. John Ferrante, (216) 433-6069
Headquarters program office: OA
Extended Mixing and Transition Control Theory Evaluated
Numerically
Considerable progress in understanding nonlinear phenomena in both unbounded and wall-bounded shear flow transition has been made by using a combination of high-Reynolds-number asymptotic and numerical methods. But we are working to fully understand the nonlinear dynamics so that, ultimately, effective means of mixing and transition control can be developed and better understanding of the source terms in the aeroacoustic noise problem achieved.
Two important aspects of the analyses are
A previously derived theory for the amplitude evolution of a two-dimensional instability wave in an incompressible mixing layer-which agrees quantitatively with available experimental data for the first nonlinear saturation stage of a plane-jet shear layer, a circular-jet shear layer, and a mixing layer behind a splitter plate-has now been extended to include a wave-interaction stage with a three-dimensional subharmonic. The ultimate wave-interaction effects can give rise to either an explosive growth or an equilibrium solution, both of which are intimately associated with the nonlinear self-interaction of the three-dimensional component. The extended theory is being evaluated numerically.
Wall-bounded shear flow transition in technological devices often occurs in regions with adverse-pressure gradients, causing the onset of turbulence usually within a relatively short streamwise distance. The unsteady flow evolves through a number of stages. For sufficiently small initial disturbances the initial nonlinear stage is associated with a resonant-triad interaction between a fundamental two-dimensional mode and a pair of oblique subharmonic modes. Some of the details depend on the relative amplitudes of the components. When the initial subharmonic amplitude is larger than that of the fundamental, the wave interaction rapidly becomes fully coupled. In the opposite situation the fundamental initially undergoes nonlinear saturation due to self-interaction effects, and subharmonic evolution becomes controlled by the parametric-resonance effects. The subharmonic amplitude continues to increase during this nonlinear-fundamental stage, even when the fundamental amplitude saturates, eventually becoming large enough to influence the fundamental. Thus, the fully coupled stage of development also occurs in this situation-but now with viscous effects being unimportant. The amplitude solutions in the fully coupled stages always end in a finite distance singularity. The theoretical predictions are being compared with available experimental results.
Bibliography
Lewis contact: Dr. Lennart S. Hultgren, (216) 433-6070
Headquarters program office: OA
The use of radiative analysis to predict temperature distributions and heat flows in partially transmitting materials is a continuing in-house effort. Composites of several layers are being analyzed where each layer can have a different refractive index. The differing refractive indices cause internal reflections at the internal interfaces and boundaries. The reflections tend to distribute energy within the layers by providing additional transmission paths in the portions of the spectrum that are not optically dense-affecting the temperature distributions within the layers.
.GIF)
The radiative transfer relations are rather complex integral equations, so it is useful to consider approximate techniques that might be incorporated more conveniently into computer design programs. One approximate technique is the two-flux method. It has the form of simultaneous differential equations and is relatively easy to solve for layers that are not optically dense. For dense layers a radiative diffusion method can be used that has the form of a single differential equation. In some recent work these methods were combined to obtain steady-state thermal behavior of a two-layer composite where one layer is optically dense. The approximate solutions were compared with numerical solutions of the radiative transfer equations.
The graph shows results for a somewhat-transparent coating (layer 1) on a substrate (layer 2) that is more optically dense. Radiative penetration is reduced in the dense substrate, and heat conduction is more dominating. The coating has two spectral absorption bands. Both external boundaries are being cooled by convection. The three sets of curves are for various levels of radiation flux incident on the hot side. Temperature distributions by the two-flux and diffusion method are in excellent agreement with the numerical solutions. The total heat flow through the composite by combined radiation and conduction agrees within better than 1% with the numerical results.
Bibliography
Last updated 1995
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