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Real-Time Adaptive Control of Mixing in a Plane Shear Layer

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Final technical rept. 15 Jul 1989-14 Dec 1993

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A control system for the enhancement and regulation of mixing in a nonreactive plane shear layer has been developed in a two-stream closed-return water facility. Mixing of a passive scalar is estimated using a thermal analog in which the two streams have uniform, steady temperatures differing by 3 C. Control is effected via an array of surface heaters flush-mounted on the flow partition and cross-stream temperature distributions are measured with a resolution of 0.03 C using an array of closely-spaced cold wire sensors. Open- loop forcing is used for the enhancement of mixing in a nonreactive plane shear layer. Mixing of a passive scalar is estimated using a thermal analog to species concentration. From the temperature distributions, a number of mixing performance measures can be calculated to describe the development of mixing with downstream distance. Further, phase-locked measurements are used to study the spatial and temporal structure of the flow and in particular the overall mixedness and composition of the flow as a function of phase in the forcing cycle. In closed-loop experiments, the position of the temperature interface between the two streams is measured in the plane of its cross stream Schlieren image by an optical sensor which is placed upstream of the rollup of the primary vortices. The output from the interface position sensor is fed back to the surface heaters. A transfer function has been developed to predict the effect of feedback on the interface motion. The dependence of various measures of mixing on the feedback gain k and the total delay time delta between the actuators and the sensors is studied.

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  • Fluid Mechanics

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