IISc Bangalore

Assessment of resolvent analysis as a tool for active flow control design

Simon Tödtli

Graduate Aerospace Laboratories

California Institute of Technology

Reducing turbulent drag on engineering surfaces such as ship hulls or pipes has the potential of tremendous energetic savings. However, tractable and efficient flow models for designing drag reduction mechanisms, such as active feedback flow control or compliant surfaces, are currently missing in the literature. This talk describes a flow model (Luhar et al, J. Fluid Mech. 2014) based on the resolvent analysis of McKeon & Sharma (J. Fluid Mech. 2010) and assesses its potential for designing active feedback flow control schemes for drag reduction in incompressible wall-bounded flows. The assessment is based on a generalized version of the well-known opposition control scheme (Choi et al, J Fluid Mech. 1994), which allows for a phase-shift between the sensor measurement and the actuator response. The resolvent model predicts that the phase shift strongly affects the attainable drag reduction and suggests that a range of nonzero phases offer improved control effectiveness. We validate these predictions by means of a parametric DNS study and show that the response of the full nonlinear system to opposition control with various phase shifts very closely follows the low-order model predictions. We close with a short discussion of the structural features of various controlled flows, which provide first insights into the role of the phase in the real flow and the physics of drag reduction.

Date(s) - 22/02/2019
4:00 pm - 6:00 pm

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