Surface actuation based flow control for low Reynolds number flow past an airfoil

Thompson, Ernold

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https://hdl.handle.net/2142/129292 Copy

Description

Title

Surface actuation based flow control for low Reynolds number flow past an airfoil

Author(s)

Thompson, Ernold

Issue Date

2025-05-05

Director of Research (if dissertation) or Advisor (if thesis)

Goza, Andres

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Aerodynamics
• Adjoint-based Optimization
• Flow Control
• Low-Re flow

Abstract

In this thesis, surface actuation for the flow past an airfoil at a Reynolds number of 1000 has been studied numerically. First, prescribed normal actuation in the form of a backward traveling wave on the suction surface with sinusoidal spatial and temporal characteristics has been studied for the purpose of lift improvement. The kinematics of actuation are defined by wavenumber and wavespeed, both of which are varied over a wide range of values to include parameters that considerably change the lift dynamics as well as those that do not. First, the effect of actuation at an angle of attack of α = 5◦ where the unactuated flow is steady is considered. Lift benefits are found to be maximal when the morphing kinematics align with the intrinsic advection velocity of the flow. Then, the role of morphing in the presence of an unsteady, separated baseline flow (with intrinsic vortex-shedding processes) at α = 15◦ is investigated. At this higher angle of attack, three distinct behavioral regimes based on the relationship between morphing and the underlying shedding frequency are identified. Actuation is found to yield lift benefits when the actuation time scales are close to those of shedding with the highest increase in mean lift occurring when the actuation frequency is slightly smaller than the shedding frequency of the unactuated flow. The influence of the actuation on the flow field is discussed in terms of the variations in the pressure field resulting from the velocity boundary condition imposed by surface actuation. The velocity boundary condition imposed by actuation is also used to describe the variations in vortex shedding behavior at α = 15◦. Although backward traveling wave on the suction surface can lead to improvements in mean lift, a concurrent increase in drag occurs. To explore actuation for the separate purposes of lift improvement and drag mitigation, in the second part of this thesis numerical optimization is used to determine the actuation for the separate goals of lift improvement and drag mitigation at α = 15◦ with actuation permissible on the entire surface of the airfoil (including the pressure side). The gradient information required by the optimization algorithm is computed in a computationally efficient way using the adjoint of the governing equations. The optimal actuation profiles for the two performance aims are compared. Where possible, similarities with actuation in the form of backward traveling waves on the suction surface have been highlighted. The flow features emerging from the optimal actuation variations, and their consequent influence on the instantaneous aerodynamic coefficients, have been analyzed.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129292

Copyright and License Information

Copyright 2025 Ernold Thompson

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