Resolvent-analysis-based design of airfoil separation control

TL;DR

This paper integrates large-eddy simulations and resolvent analysis to design and optimize active flow control on an airfoil, achieving significant drag reduction and lift increase by tuning actuation parameters based on physics-informed insights.

Contribution

It introduces a combined LES and resolvent analysis framework to predict effective actuation parameters for flow separation control on an airfoil, advancing physics-based control design.

Findings

Achieved up to 49% drag reduction and 54% lift increase with control.

Resolved actuation frequency and spanwise wavelength using resolvent analysis.

Validated resolvent analysis as a predictive tool for flow control effectiveness.

Abstract

We combine three-dimensional (3D) large-eddy simulations (LES) and resolvent analysis to design active separation control techniques on a NACA 0012 airfoil. Spanwise-periodic flows over the airfoil at a chord-based Reynolds number of $23,000$ and a free-stream Mach number of $0.3$ are considered at two post-stall angles of attack of $6^\circ$ and $9^\circ$. Near the leading edge, localized unsteady thermal actuation is introduced in an open-loop manner with two tunable parameters of actuation frequency and spanwise wavelength. For the most successful control case that achieves full reattachment, we observe a reduction in drag by up to $49\%$ and increase in lift by up to $54\%$. To provide physics-based guidance for the effective choice of these control input parameters, we conduct global resolvent analysis on the baseline turbulent mean flows to identify the actuation frequency and wavenumber that provide high energy amplification. The present analysis also considers the use of a temporal filter to limit the time horizon for assessing the energy amplification to extend resolvent analysis to unstable base flows. We incorporate the amplification and response mode from resolvent analysis to provide a metric that quantifies momentum mixing associated with the modal structure. By comparing this metric from resolvent analysis and the LES results of controlled flows, we demonstrate that resolvent analysis can predict the effective range of actuation frequency as well as the global response to the actuation input. Supported by the agreements between the results from resolvent analysis and LES, we believe that this study provides insights for the use of resolvent analysis in guiding future active flow control.