Accession Number:

ADA550440

Title:

Control of Spatially Inhomogeneous Shear Flows

Descriptive Note:

Final rept. 21 Sep 2010-21 Sep 2011

Corporate Author:

ROYAL INST OF TECH STOCKHOLM (SWEDEN) DEPT OF MECHANICS

Report Date:

2011-10-01

Pagination or Media Count:

13.0

Abstract:

It was demonstrated the possibility to delay the transition process using a feedback controller based on localized sensorsactuators. Three-dimensional TS wave packets and streaks with finite amplitudes are considered reduced-order models based on balanced truncation are built and used for the control design. The controller mitigates the disturbances amplitude when the flow is still laminar but nonlinear, resulting in a significant reduction of the perturbation energy and, later, in a delay of the transition process. The robustness of the device is tested by varying the controller effort. A too strong controller effort resulted in a worsening of the performance when the TS scenario is considered this behavior of the device is in contrast with the linear prediction. This effect is due to the excitation of higher order harmonics, related to the threedimensionality of the controller action, combined to the nonlinearities of the uncontrolled flow. Conversely, the controller built for streaks is less affected by the nonlinearities of the flow indeed, for this case, the localization is able to mimic the spatial distribution of the incoming disturbance. The resulting actuation is not introducing additional disturbances of smaller scale and the only nonlinearities are those characterizing the uncontrolled flow. Starting from this knowledge, a further improvement of the device can be achieved by explicitly accounting for the nonlinear effects during the modeling process when needed. Moreover, modern developments in robust control theory may be used to rigorously incorporate uncertainties that may be present in the design process.

Subject Categories:

  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE