Particle streak velocity field measurements in a two-dimensional mixing layer

Using digital image processing of particle streak photography, the streamwise and perpendicular components of the velocity field were investigated, in the mid‐span plane of a two‐dimensional mixing layer, with a 6:1 velocity ratio. The Reynolds number of the flow, based on the local vorticity thickness and the velocity difference across the layer, ranged from 1360 to 2520, in the plane of observation. The significant result of this experiment was that the region of vorticity bearing fluid is confined to a small fraction of the flow. A second finding, consistent with the small regions of concentrated vorticity, was the observation of instantaneous streamwise velocity reversal, in the laboratory frame, in small regions of the flow

A Cancellation Experiment in a Forced Turbulent Shear Layer

Results are presented which demonstrate that it is possible to cancel, using feedback control techniques, the effects of an externally generated disturbance in a fully-developed turbulent two-dimensional shear layer

Control of Turbulent Mixing Layers

This the final report of research conducted at the California Institute of Technology, by Paul E. Dimotakis, in collaboration with Dr. M. M. Moochesfahani as co-investigator, and with the assistance of Mr. P. Tokumaru during the last year. The primary goal was to explore ways in which open loop and closed feedback loop control methods can be utilized to affect the qualitative and quantitative behavior of turbulent shear layers. In particular, we attempted to i. investigate the dynamic behavior and response of these flows through a study of the feedback control schemes required to produce a given desired outcome, ii. explore the extent to which specific properties of turbulent shear layer flows, such as growth rate profile and mixing, can be manipulated and altered by such means, and, iii. devise schemes for producing turbulent shear layer flows with specific desirable properties, as might be dictated, for example, by the flow specifications for the efficient operation of a combustion device. In the course of this work, other derivative and closely related efforts were also undertaken, some of which will be described below. The work conducted under the sponsorship of this Grant was primarily experimental and in close collaboration with a broader experimental, numerical and theoretical effort at Caltech to study unsteady separated flows, and the evaluation and use of control techniques in these flows in particular